Chapter VIII: Systematic (1)

I. CLASSIFICATION

A. WORK OF SUCCESSIVE SYSTEMATISTS

Since the time when lichens were first recognized as a separate class—as members of the genus Lichen by Tournefort[1016] or as “Musco-fungi” by Morison[1017],—many schemes of classification have been outlined, and the history of the science of lichenology, as we have seen, is a record of attempts to understand their puzzling structure, and to express that understanding by relating them to each other and to allied classes of plants. The great diversity of opinion in regard to their affinities is directly due to their composite nature.

_a._ DILLENIUS AND LINNAEUS. The first systematists were chiefly impressed by their likeness to mosses, hepatics or algae. Dillenius[1018] in the _Historia Muscorum_ grouped them under the moss genera:—IV. _Usnea_, V. _Coralloides_ and VI. _Lichenoides_. Linnaeus[1019] classified them among algae under the general name _Lichen_, dividing them into eight orders based on thalline characters in all but one instance, the second order being distinguished from the first by bearing scutellae. The British botanists of the latter part of the eighteenth century—Hudson, Lightfoot and others—were content to follow Linnaeus and in general adopted his arrangement.

_b._ ACHARIUS. Early in the nineteenth century Acharius, the Swedish Lichenologist, worked a revolution in the classification of lichens. He gave first place to the form of the thallus, but he also noted the fundamental differences in fruit-formation: his new system appeared in the _Methodus Lichenum_[1020] with an introduction explaining the terms he had introduced, many of them in use to this day.

Diagnoses of twenty-three genera are given with their included species. The work was further extended and emended in _Lichenographia Universalis_[1021] and in the _Synopsis Lichenum_[1022]. In his final arrangement the family “Lichenes” is divided into four classes, three of which are characterized solely by apothecial characters; the fourth class has no apothecia. They are as follows:

Class I. Idiothalami with three orders, Homogenei, Heterogenei
and Hyperogenei: the apothecia differ in texture and colouration
from the thallus: _Lecidea_, _Opegrapha_, _Gyrophora_, etc.

Class II. Coenothalami, with three orders, Phymaloidei, Discoidei
and Cephaloidei. The apothecia are partly formed from the
thallus: _Lecanora_, _Parmelia_, etc. The Pyrenolichens are also
included by him in this class, because “the thallus surrounds and
is concrete with the partly or wholly immersed apothecia.”

Class III. Homothalami with two orders, Scutellati and Peltati.
The apothecia are formed from the cortical and medullary tissue
of the thallus: _Ramalina_, _Usnea_, _Collema_, etc.

Class IV. Athalami, with but one sterile genus, _Lepraria_.

The orders are thus based on the form of the fruit; the genera in the _Synopsis_ number 41. Large genera such as _Lecanora_ with 132 species are divided into sections, many of which have in turn been established as genera, by S. F. Gray in 1821, and later by other systematists.

The _Synopsis_ was the text-book adopted by succeeding botanists for some 40 years with slight alterations in the arrangement of classes, genera, etc.

Wallroth[1023] and Meyer[1024] followed with their studies on the lichen thallus, and Wallroth’s division into “Homoiomerous” and “Heteromerous” was accepted as a useful guide in the maze of forms, representing as it did a great natural distinction.

_c._ SCHAERER. This valiant lichenologist worked continuously during the first half of the nineteenth century, but with very partial use of the microscope. His last publication in 1850, an _Enumeration of Swiss Lichens_, was the final declaration of the older school that relied on field characters. His classification is as follows:

Class I. Lichenes Discoidei, with ten orders from Usneacei to
Graphidei; fruits open.

Class II. Lichenes Capitati, with three orders: Calicioidei,
Sphaerophorei and Cladoniacei; fruits stalked.

Class III. Lichenes Verrucarioidei, with three orders:
Verrucarii, Pertusarii and Endocarpei: fruits closed.

An “Appendix” contains descriptions of Crustacei and Fruticulosi, all sterile forms, except _Coniocarpon_ and _Arthonia_, which seem out of place, and finally a “Corollarium” of gelatinous lichens all classified under one genus _Collema_.

_d._ MASSALONGO AND KOERBER. As a result of their microscopic studies, these two workers proposed many changes based on fruit and spore characters, and Koerber in the _Systema Lichenum Germaniae_ (1855) gave expression to these views in his classification. He also made use of Wallroth’s distinctions of “homoiomerous” and “heteromerous,” thus dividing lichens at the outset into those mostly with blue-green and those with bright-green gonidia.

The following is the main outline of Koerber’s classification:

Series I. Lichenes Heteromerici.
Order I. Lich. Thamnoblasti (fruticose).
Order II. Lich. Phylloblasti (foliose).
Order III. Lich. Kryoblasti (crustaceous).
Series II. Lichenes Homoeomerici.
Order IV. Lich. Gelatinosi.
Order V. Lich. Byssacei.

With the exception of Order V all are subdivided into two sections, “gymnocarpi” with open fruits and “angiocarpi” with closed fruits, a distinction that had long been recognized both in lichens and in fungi.

_e._ NYLANDER. The above writers had been concerned with the interrelationships of lichens; Nylander, who was now coming forward as a lichenologist of note, gave a new turn to the study by dwelling on their relation to other classes of plants. Without for a moment conceding that they were either algal or fungal, he yet insisted on their remarkable affinity to algae on the one hand, and to fungi on the other, and he sought to make evident this double connection by his very ingenious scheme of classification[1025]. He began with what we may call “algal lichens,” those associated with blue-green gonidia in the family “Collemacei”; he continued the series to the most highly evolved foliose forms and then wound up with those that are most akin to fungi, that is, those with least apparent thalline formation—according to him—the “Pyrenocarpei.”

In his scheme, which is the one followed by Leighton and Crombie, the “family” represents the highest division; series, tribe, genus and species come next in order. We have thus:

Fam. I. Collemacei.
Fam. II. Myriangiacei (now reckoned among fungi).
Fam. III. Lichenacei.

This last family, which includes the great bulk of lichens, is divided into the following series: I. Epiconiodei; II. Cladoniodei; III. Ramalodei; IV. Phyllodei; V. Placodei; VI. Pyrenodei. It is an ascending series up to the Phyllodei, or foliaceous lichens, which he considers higher in development than the fruticose or filamentous Ramalodei. The Placodei include four tribes on a descending scale, the Lecanorei, Lecidinei, Xylographidei and Graphidei. The classification is almost wholly based on thalline form, except for the Pyrenodei in which are represented genera with closed fruits, there being one tribe only, the Pyrenocarpei.

Nylander claims however to have had regard equally to the reproductive system and was the first to give importance to the spermogonia. The classification is coherent and easy to follow, though, like all classifications based on imperfect knowledge, it is not a little artificial; also while magnifying the significance of spermogonia and spermatia, he overlooked the much more important characters of the ascospores.

_f._ MÜLLER(-ARGAU). In preparing his lists of Genevan lichens (1862), Müller realized that Nylander’s series was unnatural, and he found as he studied more deeply that lichens must be ranged in parallel or convergent but detached groups. He recognized three main groups:

1. Eulichens, divided into Capitularieae, Discocarpeae and
Verrucaroideae.
2. Epiconiaceae.
3. Collemaceae.

He suggested that, in relation to other plants, Eulichens approach Pezizae, Hysteriaceae and Sphaeriaceae; Epiconiaceae have affinity with Lycoperdaceae, while Collemaceae are allied to the algal family Nostocaceae. These three groups of Eulichens, he held, advanced on somewhat parallel lines, but reached a very varied development, the Discocarpeae attaining the highest stage of thalline form. Müller accepted as characters of generic importance the form and structure of the fruiting body, the presence or absence of paraphyses, and the septation, colour, etc. of the spores.

A few years later (1867) the composite nature of the lichen thallus was announced by Schwendener, and, after some time, was acknowledged by most botanists to be in accordance with the facts of nature. Any system of classification, therefore, that claims to be a natural one, must, while following as far as possible the line of plant development, take into account the double origin of lichens both from algae and fungi, the essential unity and coherence of the class being however proved by the recurring similarity between the thalline types of the different phyla. As Müller had surmised: “they are a series of parallel detached though convergent groups.”

_g._ REINKE. The arrangement of Ascolichens on these lines was first seriously studied by Reinke[1026], and his conclusions, which are embodied[1027] in the _Lichens of Schleswig-Holstein_, have been largely accepted by succeeding workers. He recognizes three great subclasses: 1. Coniocarpi; 2. Discocarpi; 3. Pyrenocarpi.

The Coniocarpi are a group apart, but as their fruit is at first entirely closed—at least in some of the genera—the more natural position for them is between Discocarpi and Pyrenocarpi. It is in the arrangement of the Discocarpi that variation occurs. Reinke’s arrangement of orders and families in that sub-class is as follows:

Subclass 2. Discocarpi.

Order I. _GRAMMOPHORI_: Fam. _GRAPHIDACEI_ and _XYLOGRAPHACEI_.

Order II. _LECIDEALES_: Fam. _GYALECTACEI_, _LECIDEACEI_,
_UMBILICARIACEI_ and _CLADONIACEI_.

Order III. _PARMELIALES_: Fam. _URCEOLARIACEI_, _PERTUSARIACEI_,
_PARMELIACEI_, _PHYSCIACEI_, _TELOSCHISTACEI_ and
_ACAROSPORACEI_.

Order IV. _CYANOPHILI_: Fam. _LICHINACEI_, _EPHEBACEI_,
_PANNARIACEI_, _STICTACEI_, _PELTIGERACEI_,
_COLLEMACEI_ and _OMPHALARIACEI_.

The orders represent generally the principal phyla or groups, the families subordinate parallel phyla within the orders. The first three orders are stages of advance as regards fruit development; the Cyanophili are a group apart.

Wainio[1028] rendered great service to Phylogeny in his elaborate work on Cladoniaceae, the most complicated of all the lichen phyla. He also drew up a scheme of arrangement in his work on Brazil Lichens[1029]. There is in it some divergence from Reinke’s arrangement, as he tends to give more importance to the thallus than to fruit characters as a guide. He places, for instance, Gyrophorei beside Parmelei and at a long distance from his Lecidei. The Cyanophili group of families he has interpolated between _Buelliae_ (Physciaceae) and _Lecideae_. Many workers approve of Wainio’s classification but it presents some difficult problems.

_h._ ZAHLBRUCKNER. The systematist of greatest weight in recent times is A. Zahlbruckner, who is responsible for the systematic account of lichens in Engler and Prantl’s _Natürlichen Pflanzenfamilien_. It is difficult to express the very great service he has rendered to Lichenology, in that and other world-wide studies of lichens. The sketch of lichen phylogeny as given in the present volume owes a great deal to the sound and clear guidance of his work, though his conclusions may not always have been accepted. The classification in the _Pflanzenfamilien_ is the one now generally followed.

The class _Lichenes_ is divided by Zahlbruckner[1030] into two subclasses, I. Ascolichens and II. Hymenolichens. He gives a third class, Gasterolichens[1031], but as it was founded on error[1032], it need not concern us here. The Ascolichens are by far the more important. These are subdivided into:

Series 1. =PYRENOCARPEAE=, with perithecial fruits.
Series 2. =GYMNOCARPEAE=, with apothecial fruits.

These are again broken up into families, and in the arrangement and sequence of the families Zahlbruckner indicates his view of development and relationship. They occur in the following order:

SERIES 1. =PYRENOCARPEAE=

ALGAL CELLS PROTOCOCCACEAE OR _PALMELLA_.

I. _MORIOLACEAE._ }
}
II. _EPIGLOEACEAE._ } Thallus crustaceous, perithecia solitary.
}
III. _VERRUCARIACEAE._ }

IV. _DERMATOCARPACEAE._ Thallus squamulose or foliose.

V. _PYRENOTHAMNIACEAE._ Thallus fruticose.
ALGAL CELLS _PRASIOLA_.

VI. _MASTOIDIACEAE._
ALGAL CELLS _TRENTEPOHLIA_.

VII. _PYRENULACEAE._ }
} Thallus crustaceous, perithecia occurring
VIII. _PARATHELIACEAE._ } singly.

IX. _TRYPETHELIACEAE._ }
} Thallus crustaceous, perithecia united
X. _ASTROTHELIACEAE._ } (stromatoid).

XI. _MYCOPORACEAE._ Thallus crustaceous, perithecia in compact
groups with a common outer wall.

XII. _PHYLLOPYRENIACEAE._ Thallus minutely foliose.
ALGAL CELLS _PHYLLACTIDIUM_ OR _MYCOIDEA_.

XIII. _STRIGULACEAE._ Tropical leaf-lichens.
ALGAL CELLS _NOSTOC_ OR _SCYTONEMA_.

XIV. _PYRENIDIACEAE._ Thallus minutely squamulose or fruticose.

SERIES 2. =GYMNOCARPEAE=

Subseries 1. Coniocarpineae, with subperithecial fruits.
Subseries 2. Graphidineae, with elongate, narrow fruits.
Subseries 3. Cyclocarpineae, with round open fruits.

SUBSERIES 1. =CONIOCARPINEAE=

This is a well-defined group, peculiar in the disappearance of the asci at an early stage so that the spores lie like a powder in the globose partly closed fruits. Algal cells, bright-green; Protococcaceae. There are only three families:

XV. _CALICIACEAE._ Thallus crustaceous, apothecia stalked.

XVI. _CYPHELIACEAE._ Thallus crustaceous, apothecia sessile.

XVII. _SPHAEROPHORACEAE._ Thallus foliose or fruticose, apothecia
sessile.

SUBSERIES 2. =GRAPHIDINEAE=

This subseries comes next in the form of fruit development; generally the apothecia are elongate, with a narrow slit-like opening, so that a transverse section shows almost a perithecial outline. Algal cells are mostly _Trentepohlia_.

XVIII. _ARTHONIACEAE._ Thallus crustaceous, apothecia oval or linear,
flat.

XIX. _GRAPHIDACEAE._ Thallus crustaceous, apothecia linear, raised.

XX. _CHIODECTONACEAE._ Thallus crustaceous, apothecia generally
immersed in a stroma.

XXI. _DIRINACEAE._ Thallus crustaceous, corticate above, apothecia
round.

XXII. _ROCCELLACEAE._ Thallus fruticose, apothecia round or elongate.

SUBSERIES 3. =CYCLOCARPINEAE=

A large and very varied group! In most of the families the algal cells are bright-green (Chlorophyceae), in some they are blue-green (Cyanophyceae), these latter corresponding to Reinke’s order Cyanophili. The apothecia, as the name implies, are round and open; the “Cyanophili” have been placed by Zahlbruckner after those families in which the apothecium has no thalline margin. They form a phylum distinct from those that precede and those that follow.

The first family of the Cyclocarpineae, the Lecanactidaceae, is often placed under Graphidineae; in any case it forms a link between the two subseries.

1. _Lecideine group_ (apothecia without a thalline margin).

XXIII. _LECANACTIDACEAE._ Thallus crustaceous. Algal cells
_Trentepohlia._ Apothecium with
carbonaceous hypothecium or parathecium.

XXIV. _PILOCARPACEAE._ Thallus crustaceous. Algal cells
Protococcaceae. Apothecia with a dense
rather dark hypothecium.

XXV. _CHRYSOTHRICACEAE._ Thallus felted, loose in texture. Algal
cells _Palmella_, Protococcaceae or
_Trentepohlia_. Apothecia with or without
a thalline margin. The affinity of the
“Family” seems to be with Pilocarpaceae.

XXVI. _THELOTREMACEAE._ } Thallus crustaceous. Algal cells in the
XXVII. _DIPLOSCHISTACEAE._ } first _Trentepohlia_; in the second
} Protococcaceae. In both there are
} prominent double margins round the
} apothecium.

XXVIII. _ECTOLECHIACEAE._ Thallus very primitive in type. Algal cells
Protococcaceae. Apothecia with or without
a thalline margin. Nearly related to
Chrysothricaceae.

XXIX. _GYALECTACEAE._ Thallus crustaceous. Algal cells _Trentepohlia_,
_Phyllactidium_ or rarely _Scytonema_.
Apothecia biatorine, _i.e._ of soft
consistency and without gonidia.

XXX. _COENOGONIACEAE._ Thallus confusedly filamentous (byssoid).
Algal cells _Trentepohlia_ or _Cladophora_.
Apothecia biatorine.

XXXI. _LECIDEACEAE._ Thallus crustaceous or squamulose. Algal cells
Protococcaceae. Apothecia biatorine (soft), or
lecideine (carbonaceous).

XXXII. _PHYLLOPSORACEAE._ Thallus squamulose or foliose. Algal cells
Protococcaceae. Apothecia biatorine or
lecideine.

XXXIII. _CLADONIACEAE._ Thallus twofold. Algal cells Protococcaceae.
Apothecia biatorine or lecideine.

XXXIV. _GYROPHORACEAE._ Thallus foliose. Algal cells Protococcaceae.
Apothecia lecideine.

XXXV. _ACAROSPORACEAE._ Thallus primitive crustaceous, squamulose or
foliose. Algal cells Protococcaceae.
Apothecia with or without a thalline
margin; very various, but always with
many-spored asci.

2. _Cyanophili group._

In this group the classification depends almost entirely on the nature of the algal constituents. The apothecia are in most genera provided with a thalline margin.

_a. More or less gelatinous when moist._

XXXVI. _EPHEBACEAE._ Algal cells _Scytonema_ or _Stigonema_. Thallus
minutely fruticose or filamentous.

XXXVII. _PYRENOPSIDACEAE._ Algal cells _Gloeocapsa_ (_Gloeocapsa_,
_Xanthocapsa_ or _Chroococcus_). Thallus
crustaceous, minutely foliose or fruticose.

XXXVIII. _LICHINACEAE._ Algal cells _Rivularia_. Thallus crustaceous,
squamulose or minutely fruticose.

XXXIX. _COLLEMACEAE._ Algal cells _Nostoc_. Thallus crustaceous,
minutely fruticose, or squamulose to foliose.

XL. _HEPPIACEAE._ Algal cells _Scytonema_. Thallus generally
squamulose and formed of plectenchyma.

_b. Not gelatinous when moist._

XLI. _PANNARIACEAE._ Algal cells _Nostoc_, _Scytonema_ or rarely
bright-green, Protococcaceae. Thallus
crustaceous, squamulose or foliose.

XLII. _STICTACEAE._ Algal cells _Nostoc_ or Protococcaceae. Thallus
foliose, and very highly developed, corticate
on both surfaces.

XLIII. _PELTIGERACEAE._ Algal cells _Nostoc_ or Protococcaceae.
Thallus foliose, corticate above.

3. _Lecanorine group_ (apothecia with a thalline margin).

The remaining families have all bright-green gonidia and nearly always apothecia with a thalline margin. The group includes several distinct phyla:

XLIV. _PERTUSARIACEAE._ Thallus crustaceous. Apothecia, one or
several immersed in thalline tubercles;
spores mostly very large.

XLV. _LECANORACEAE._ Thallus crustaceous or squamulose. Apothecia
mostly superficial.

XLVI. _PARMELIACEAE._ Thallus foliose, rarely almost fruticose or
filamentous. Apothecia scattered over the
surface or marginal, sessile.

XLVII. _USNEACEAE._ Thallus fruticose or filamentous. Apothecia
sessile or shortly stalked.

XLVIII. _CALOPLACACEAE._ Thallus crustaceous, squamulose or minutely
fruticose. Apothecia with polarilocular
colourless spores.

XLIX. _TELOSCHISTACEAE._ Thallus foliose or fruticose. Apothecia with
polarilocular colourless spores.

L. _BUELLIACEAE._ Thallus crustaceous or squamulose. Apothecia
(lecideine or lecanorine) with two-celled,
thick-walled brown spores (polarilocular in
part).

LI. _PHYSCIACEAE._ Thallus foliose, rarely partly fruticose.
Apothecia with two-celled thick-walled brown
spores (polarilocular in part).

Subclass 2. Hymenolichens.

There are only three closely related genera of Hymenolichens, _Cora_, _Corella_ and _Dictyonema_ with _Chroococcus_ or _Scytonema_ algae.

There is reason to dissent from the arrangement in one or two instances which will be pointed out in the following examination of families and genera.

B. FAMILIES AND GENERA OF ASCOLICHENS

The necessity for a well-reasoned and well-arranged system of classification is self-evident: without a working knowledge of the plants that are the subject of study no progress can be made. The recognition of plants as isolated individuals is not sufficient, it must be possible to place them in relation to others; hence the importance of a natural system. In identifying species artificial aids, such as habitat and substratum, are also often of great value, and a good working system should take account of all characteristics.

Lichen development is the result of two organisms mutually affecting each other, but as the fungus provides the reproductive system, it is the dominant partner: the main lines of classification are necessarily determined by fruit characters. The algae occupy a subsidiary position, but they also are of importance in shaping the form and structure of the thallus. The different phyla are often determined by the presence of some particular alga; it is in the delimitation of families that the algal influence is of most effect.

Zahlbruckner’s system gives due weight to the inheritance from both fungus and alga with, however, the fungus as the chief factor in development, and as his work is certain to be generally followed by modern lichenologists, it is the one of most immediate interest. His scheme has been accepted in the following more detailed account of families and genera, and for the benefit of home workers those that have not so far been recorded from the British Isles have been marked with an asterisk.

It cannot be affirmed that nomenclature is as yet firmly established in lichenology. Both on historical grounds and on those of convenience, the subject is one of extreme importance, and interest in it is one of the main avenues by which we secure continuity with the past, and by which we are able to realize not only the difficulty, but the romance of pioneer work. Besides, there can be no exchange of opinion between students nor assured knowledge of plants, until the names given to them are beyond dispute. According to the ruling of the Brussels Botanical Congress in 1910, Linnaeus’s[1033] list of lichens in the _Species Plantarum_ has been selected as the basis of nomenclature, but since his day many new families, genera and species have been described and often insufficiently delimited. It is not easy to decide between priority, which appeals to the historical sense, and recent use which is the plea of convenience. Here also it seems there can be no rigid decision; the one aim should be to arrive at a conclusion satisfactory to all, and accepted by all.

In the following necessarily brief account of families and genera, the “spermogonia” or “pycnidia” have in most cases been left out of account, as in many instances they vary within the family and occasionally even within the genus. Their taxonomic value is not without importance, but, in the general systematic arrangement, they are only subsidiary characters. An account of them has already been given, and for more detailed statements the student is referred to purely systematic works.

There are two main types of spore production in the “pycnidia” which have been shortly described by Steiner[1034] as “exobasidial” and “endobasidial.” In the former the sporophores are simple or branched filaments, at the apices of which a short process grows out and buds off a pycnidiospore; in the latter the spores are budded directly from cells lining the walls or filling the cavity of the pycnidium. The exobasidial type is more simply rendered in the following pages by “acrogenous,” the endobasidial by “pleurogenous” spore production. In many cases the “spermogonia” or “pycnidia” are still imperfectly known. In designating the gonidial algae, the more comprehensive Protococcaceae has been substituted for _Protococcus_, as in many cases the alga is probably not _Protococcus_ as now understood, but some other genus of the family[1035].

SUBCLASS I. ASCOLICHENS

SERIES I. PYRENOCARPINEAE

It is on mycological grounds that Pyrenocarpineae are placed at the base of lichen classification. There is no evidence that the series was first in time.

I. _MORIOLACEAE_

This family was described by Norman[1036] in 1872 from specimens collected by himself in Norway or in the Tyrol, on soil or more frequently on trees. There seems to have been no further record, and Zahlbruckner, while accepting the family, suggests that an examination or revision may be necessary.

The thallus is crustaceous. The algal cells, Protococcaceae, occur either in groups (sometimes stalked) surrounded by a plectenchymatous wall and called by Norman “goniocysts,” or they form nests in the thallus termed “nuclei” which are surrounded by a double wall of plectenchyma, colourless in the interior and brown outside. Norman invented the term “Allelositismus,” which may be rendered “mutualism,” to indicate this peculiar form of thallus. The species of _Spheconisca_ are fairly numerous on poplars, willows and conifers:

Algae in “goniocysts” 1. *Moriola Norm.[1037]
Algae in double-walled “nuclei” 2. *Spheconisca Norm.

II. _EPIGLOEACEAE_

The family consists of but one genus and one species, _Epigloea bactrospora_, and, according to Zahlbruckner, further examination is necessary to make certain as to the lichenoid nature of the plant.

Zukal[1038] found the perithecia scattered over the leaves of mosses, and he alleges that hyphae connected with the perithecium were closely associated with the alga, _Palmella botryoides_, and were causing it no harm. Along with the perithecia he also found minute pycnidia. The “thallus” is of a gelatinous nature and homoiomerous in structure; the perithecia are soft and clear-coloured with many-spored asci and colourless one-septate spores.

The small globose pycnidia contain simple sporophores and acrogenous straight or slightly bent rod-like spores.

Asci many-spored; spores one-septate 1. *Epigloea Zukal.

III. _VERRUCARIACEAE_

In all the genera of this family the thallus is crustaceous, and, with very few exceptions, the species are saxicolous or terricolous. The thallus is variable within the crustaceous limits, and may be superficial and very conspicuous, almost imperceptible, or wholly immersed in the substratum. The algal cells are Protococcaceae, and in two of the genera the green cells penetrate the hymenium and grow in rows alongside of the asci. The perithecia are small roundish structures scattered over the thallus, the base immersed, but the upper portion generally projecting. An outer dark-coloured wall surrounds the whole perithecium (entire) or only the upper exposed portion (dimidiate); it opens above by a pore or ostiole more or less prominent.

In some of the genera the paraphyses become dissolved at an early stage, and somewhat similar filaments near the ostiole, termed periphyses, aid in the expulsion of the spores. The spores vary in septation, colour and size, and these variations have served to delimit the genera which have been formed from the original very large genus _Verrucaria_. The ascus may be 1-, 2-, 4- or 8-spored. In only one genus is it many-spored (_Trimmatothele_).

The genera are as follows:

Perithecia with simple ostioles.
Paraphyses disappearing early, or wanting.
Spores simple, ellipsoid 1. Verrucaria Web.
Spores simple, elongate vermiform 2. Sarcopyrenia Nyl.
Spores simple, numerous in the ascus 3. *Trimmatothele Norm.
Spores 1-3-septate 4. Thelidium Massal.
Spores muriform (with transverse and
longitudinal divisions).
Without hymenial gonidia 5. Polyblastia Massal.
With hymenial gonidia 6. Staurothele Norm.
Paraphyses present.
Spores simple.
Without hymenial gonidia 7. Thrombium Wallr.
With hymenial gonidia 8. *Thelenidia Nyl.
Spores 3-septate, broadly ellipsoid 9. *Geisleria Nitschke.
Spores acicular, many-septate 10. Gongylia Koerb.
Spores muriform 11. Microglaena Lönnr.
Perithecia with a wide ring round the ostiole.
Spores muriform; paraphyses
unbranched 12. *Aspidothelium Wain.
Spores elongate, many-septate;
paraphyses branched 13. *Aspidopyrenium Wain.

IV. _DERMATOCARPACEAE_

In this family there is a much more advanced thalline development—generally squamulose or with some degree of foliose structure, though in the genus _Endocarpon_, some of the species are little more than crustaceous. The gonidia are bright-green Protococcaceae (according to Chodat, _Coccobotrys_ in _Dermatocarpon_). In _Endocarpon_ they appear in the hymenium.

The least developed in structure is _Normandina_: the thallus of the single species consists of delicate shell-like squamules which are non-corticate above and below. In the other genera there is a cortex of plectenchyma.

The perithecia are almost wholly immersed, and open above by a straight ostiole. The fructification of _Dacampia_ is considered by some lichenologists to be only a parasite on the white thickish squamulose thallus with which it is associated.

Hymenial gonidia present.
Spores muriform 1. Endocarpon Hedw.
Hymenial gonidia absent.
Thallus non-corticate 2. Normandina Wain.
Thallus corticate.
Spores simple, colourless 3. Dermatocarpon Eschw.
Spores simple, brown 4. *Anapyrenium Müll.-Arg.
Spores elongate-septate, colourless 5. *Placidiopsis Beltr.
Spores elongate-septate, brown 6. *Heterocarpon Müll.-Arg.
Spores muriform, colourless 7. *Psoroglaena Müll.-Arg.
Spores muriform, brown 8. Dacampia Massal.

V. _PYRENOTHAMNIACEAE_

Thallus more or less fruticose and corticate on both surfaces. Algal cells Protococcaceae.

Only two genera are included in this family: _Nylanderiella_ with one species from New Zealand, with a small laciniate thallus up to 15 mm. in height, partly upright, partly decumbent, and attached to the substratum by basal rhizinae; the other small genus, _Pyrenothamnia_, belongs to N. America; the thallus has a short rounded stalk which expands above to an irregular frond. The perithecia are immersed in the fronds.

Spores colourless, 1-septate 1. *Nylanderiella Hue[1039].
Spores brown, muriform 2. *Pyrenothamnia Tuckerm.

VI. _MASTOIDEACEAE_

A family containing one genus and one species, with a wide distribution, having been found in Siberia, on the Antarctic continent (Graham’s Land), as also in Tierra del Fuego, South Georgia, South Shetland Islands and Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae. Algal cells _Prasiola_[1040]. The perithecia are globose and partly project from the thallus; the asci are 8-spored; the paraphyses are mucilaginous and partly dissolving.

Spores elongate-fusiform, simple,
colourless 1. *Mastoidea Hook. and Harv.

VII. _PYRENULACEAE_

This family of crustaceous lichens differs from Verrucariaceae chiefly in the gonidium which is a species of _Trentepohlia_. Genera and species are largely corticolous and the thallus is inconspicuous, often developing within the substratum. The perithecia, like those of _Verrucariae_, are immersed or partly emergent and have an entire or dimidiate outer wall. They are scattered over the thallus except in _Anthracothecium_ where they are often coalescent. This genus is tropical or subtropical except for one species which inhabits S.W. Ireland.

Paraphyses are variable, and in some species tend to disappear, but do not dissolve in mucilage. The spores are generally colourless, only in one monotypic genus, _Coccotrema_, are they simple. The cells into which the spore is divided differ in form according to the genus.

Paraphyses branched and entangled or wanting.
Perithecia opening above by stellate
lobes 1. *Asteroporum Müll.-Arg.
Perithecia opening by a pore.
Spores variously septate.
Spore cells cylindrical or cuboid.
Spores colourless, elongate or
ovate 1-5-septate 2. Arthopyrenia Massal.
Spores colourless, filiform
1-multi-septate 3. Leptorhaphis Koerb.
Spores colourless, muriform 4. Polyblastropsis A. Zahlbr.
Spores brown, ovoid or elongate
2-5-septate 5. Microthelia Koerb.
Spore cells globose or lentiform,
3-multi-septate 6. *Pseudopyrenula Müll.-Arg.
Paraphyses unbranched free.
Spore cells cylindrical or cuboid.
Perithecia beset with hairs 7. *Stereochlamys Müll.-Arg.
Perithecia naked.
Asci disappearing; spores elongate
multi-septate, colourless 8. *Belonia Koerb.
Asci persistent.
Spores simple, ellipsoid,
colourless 9. *Coccotrema Müll.-Arg.
Spores elongate, 1-multi-septate,
colourless 10. Porina Müll.-Arg.
Spores elongate, 1-multi-septate,
brown 11. Blastodesmia Massal.
Spores muriform, colourless 12. *Clathroporina Müll.-Arg.
Spores elongate, 2-3-septate,
colourless 13. Thelopsis Nyl.
Spore cells globose or lentiform.
Spores elongate, 1-5-septate,
brown 14. Pyrenula Massal.
Spores muriform, brown 15. Anthracothecium Massal.

VIII. _PARATHELIACEAE_

This family is peculiar in that the perithecia open by a somewhat elongate ostiole that slants at an oblique angle. The algal cells are _Trentepohlia_. Genera and species are endemic in tropical or subtropical regions of the Western hemisphere, though a species of _Pleurotrema_ has been found in subantarctic America. They are corticolous and the thallus is either superficial or embedded. The genera are arranged according to spore characters:

Spores elongate, 2- or more-septate.
Spore cells cylindrical, colourless 1. *Pleurotrema Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Plagiotrema Müll.-Arg.
Spores brown 3. *Parathelium Müll.-Arg.
Spores muriform.
Spores colourless 4. *Campylothelium Müll.-Arg.
Spores brown 5. *Pleurothelium Müll.-Arg.

IX. _TRYPETHELIACEAE_

This and the following two families are distinguished by the pseudostroma or compound fruit, a character rare among lichens, though the true stroma is frequent in Pyrenomycetes in such genera as _Dothidea_, _Valsa_, etc. The genera are crustaceous and corticolous and occur with few exceptions in tropical or subtropical regions, mostly in the Western Hemisphere. Several grow on officinal bark (_Cinchona_, etc.). Algal cells are _Trentepohlia_. As in many tropical lichens, the spores are large. The genera are based chiefly on spore characters, on septation, and on the form of the spore cells:

Spore cells cylindrical or cuboid.
Spores colourless, elongate,
multi-septate 1. *Tomasiella Müll.-Arg.
Spores colourless, muriform 2. *Laurera Rehb.
Spores brown, muriform 3. *Bottaria Massal.
Spore cells globose-lentiform.
Spores colourless, elongate,
multi-septate 4. *Trypethelium Spreng.
Spores brown, elongate, multi-septate 5. Melanotheca Müll.-Arg.

X. _ASTROTHELIACEAE_

The perithecia are either upright or inclined, and occur usually in radiate groups. They are free or united in a stroma, and the elongate ostioles open separately or coalesce in a common canal. The genera are all crustaceous, with _Trentepohlia_ gonidia. They are tropical or subtropical, mostly in the Western Hemisphere; but species of _Parmentaria_ and _Astrothelium_ have been recorded also from Australia.

The spores are all many-celled and the form of their cells is a generic character:

Spores elongate, multi-septate.
Spore cells cylindrical 1. *Lithothelium Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Astrothelium Trev.
Spores brown 3. *Pyrenastrum Eschw.
Spores muriform.
Spores colourless 4. *Heufleria Trev.
Spores brown 5. *Parmentaria Fée.

XI. _MYCOPORACEAE_

A small family with only two genera which are found in both Hemispheres; species of both occur in Great Britain. They are all corticolous. The perithecia are united into a partially chambered fruiting body surrounded by a common wall, but opening by separate ostioles. The thallus is thinly crustaceous, with _Palmella_ gonidia in _Mycoporum_, and _Trentepohlia_ in _Mycoporellum_. The spores are colourless or brown in both genera:

Spores muriform 1. Mycoporum Flot.
Spores elongate, multi-septate 2. Mycoporellum A. Zahlbr.

XII. _PHYLLOPYRENIACEAE_

Thallus foliose with both surfaces corticate and attached by rhizinae. Algal cells _Trentepohlia_. There is but one genus, _Lepolichen_, which has a laciniate somewhat upward growing thallus. Two species, both from South America, have been described, _L. granulatus_ Müll.-Arg. and _L. coccophora_ Hue. The latter has been recently examined by Hue[1041] who finds, on the thalli, cephalodia which are peculiar in containing bright-green gelatinous algae either _Urococcus_ or _Gloeocystis_, one of the few instances known of chlorophyllaceous algae forming part of a cephalodium. _Gloeocystis_ may be the only alga present in the cephalodium; _Urococcus_ is always accompanied by _Scytonema_.

The perithecia are immersed in thalline tubercles:

Spores colourless, simple, ovoid or
ovoid-elongate 1. *Lepolichen Trevis.

XIII. _STRIGULACEAE_

A family of epiphyllous lichens inhabiting and disfiguring coriaceous evergreen leaves, or occasionally fern leaves in tropical or subtropical regions. The algae associated are _Mycoidea_ and _Phycopeltis_ (_Phyllactidium_). The only truly parasitic lichen, _Strigula_, belongs to this family: the alga precedes the lichen on the leaves and is gradually invaded by the hyphae of the lichen and altered in character. The small black perithecia are scattered over the surface. In _Strigula_ the lichen retains the spreading rounded form of the alga. The other genera are more irregular.

Thallus orbicular in outline 1. *Strigula Fries.
Thallus irregular.
Perithecia without hairs.
Spores colourless.
Spores elongate, multi-septate 2. *Phylloporina Müll.-Arg.
Spores muriform 3. *Phyllobathelium Müll.-Arg.
Spores brown.
Spores simple 4. *Haplopyrenula Müll.-Arg.
Spores elongate, 1-3-septate 5. *Microtheliopsis Müll.-Arg.
Perithecia beset with stiff hairs 6. *Trichothelium Müll.-Arg.

XIV. _PYRENIDIACEAE_

The only family of Pyrenocarpineae associated with blue-green algae. The genera of Pyrenidiaceae are all monotypic, only one is common and of wide distribution, _Coriscium_ (_Normandina_ Nyl.). _Pyrenidium_ is the only member that has a fruticose thallus, and that is of minute dimensions. _Eolichen Heppii_, found and described by Zukal, is a doubtful lichen. “_Lophothelium_” Stirton is a case of parasitism of a fungus, _Ticothecium_, on the squamules of _Stereocaulon condensatum_.

Algal cells _Scytonema_ or _Stigonema_.

Thallus crustaceous[1042]; spores simple,
colourless 1. *Rhabdopsora Müll.-Arg.
Thallus crustaceous; spores 1-septate,
colourless 2. *Eolichen Zuk.
Thallus crustaceous; spores muriform,
brown 3. *Pyrenothrix Riddle[1043].
Thallus squamulose; spores numerous,
simple 4. *Placothelium Müll.-Arg.

Algal cells _Nostoc_.

Thallus crustaceous; spores filiform,
simple, colourless 5. *Hassea A. Zahlbr.
Thallus fruticose; spores elongate,
3-septate, brown 6. Pyrenidium Nyl.

Algal cells _Microcystis_ (_Polycoccus_).

Thallus squamulose; fructification
unknown 7. Coriscium Wainio.

SERIES II. =GYMNOCARPEAE=

SUBSERIES 1. =Coniocarpineae=

This small subseries is marked by the peculiar “mazaedium” type of fruit with its disappearing asci. It forms a connecting link between the families with perithecia and those with apothecia. The thallus is crustaceous or fruticose, often poorly developed and sometimes absent. The algal cells are Protococcaceae or rarely _Trentepohlia_.

XV. _CALICEACEAE_

The thallus is thinly crustaceous, sometimes brightly coloured, sometimes absent, taking no part in the formation of the fruits; these have upright stalks with a small capitulum, and often look like minute nails. One genus, _Sphinctrina_, is parasitic on the thallus of other lichens, mostly _Pertusariae_.

Fruits with slender stalks.
Spores simple.
Spores colourless 1. Coniocybe Ach.
Spores brown 2. Chaenotheca Th. Fr.
Spores septate, brown.
Spores 1-septate 3. Calicium De Not.
Spores 3-7-septate 4. Stenocybe Nyl.
Fruits with short thick stalks.
Spores globose, brown (parasitic) 5. Sphinctrina Fries.
Spores 1-septate, brown 6. *Pyrgidium Nyl.

XVI. _CYPHELIACEAE_

Thallus crustaceous. Algal cells Protococcaceae or _Trentepohlia_. Apothecia sessile, more widely open than in the previous family; in some genera the thallus forms an outer apothecial margin. The genera _Farriola_ from Norway and _Tylophorella_ from New Granada are monotypic. The British genus _Cyphelium_ has been known as _Trachylia_.

Thallus with Protococcaceae.

Spores colourless, simple 1. *Farriola Norm.
Spores brown, 1-3-septate (rarely simple
or muriform) 2. Cyphelium Th. Fr.

Thallus with _Trentepohlia_.

Spores simple, many in the ascus 3. *Tylophorella Wainio.
Spores 8 in the ascus.
Apothecia with a thalline margin 4. *Tylophoron Nyl.
Apothecia without a thalline margin 5. *Pyrgillus Nyl.

XVII. _SPHAEROPHORACEAE_

The most highly evolved family of the subseries, as regards the thallus. Algal cells Protococcaceae. In _Tholurna_, a small lichen endemic in Scandinavia, there is a double thallus: one of horizontal much-divided squamules, the other swollen, upright, terminating in the capitulum. The fruit is lateral in _Calycidium_, a squamulose form from New Zealand, and in _Pleurocybe_ from Madagascar, with stiff strap-shaped fronds. All the genera are monotypic except _Sphaerophorus_, of which genus ten species are recorded, some of them with a world-wide distribution. The spores are brown and simple or 1-septate.

Thallus squamulose and upright 1. *Tholurna Norm.
Thallus wholly squamulose 2. *Calycidium Stirton.
Thallus fruticose.
Fronds hollow in the centre 3. *Pleurocybe Müll.-Arg.
Fronds not hollow.
Fruit without a thalline margin 4. *Acroscyphus Lév.
Fruit inclosed in the tip of the
fronds 5. Sphaerophorus Pers.

SUBSERIES 2. =Graphidineae=

In this subseries are included five families that differ rather widely from each other both in thallus and apothecia; the latter are more or less carbonaceous and mostly with a proper margin only. Families and genera are widely distributed, though most abundant in warm regions. Algal cells mostly _Trentepohlia_.

A comprehensive study of the apothecia of this series by Bioret[1044] gives some interesting results in regard to the paraphyses: in _Arthonia_ they are irregular in direction and much-branched; in _Opegrapha_, the paraphyses are vertical and parallel with more regular branching; _Stigmatidium_ (_Enterographa_) resembles _Opegrapha_ in this respect as does also _Platygrapha_, a genus of Lecanactidaceae, while in _Graphis_ the paraphyses are vertical, unbranched and free; _Melaspilea_ paraphyses are somewhat similar to those of _Graphis_.

XVIII. _ARTHONIACEAE_

The thallus of Arthoniaceae is corticolous with few exceptions and is very inconspicuous, being largely embedded in the substratum. The apothecia (ardellae) are round, irregular or stellate, without any margin, the hymenium being protected by the dense branching of the paraphyses at the tips.

_Arthonia_ is abundant everywhere. The species of the other genera belong mostly to tropical or subtropical countries. _Arthoniopsis_ is similar to _Arthonia_ in the character of the fruits, but the gonidium is a _Phycopeltis_, and it is only found on leaves. _Synarthonia_ with peculiar stromatoid fructification is monotypic; it occurs in Costa Rica.

Thallus with _Trentepohlia_ gonidia.

Apothecia scattered.
Spores elongate 1- or pluri-septate 1. Arthonia Ach.
Spores muriform 2. Arthothelium Massal.
Apothecia stromatoid.
Spores elongate, multi-septate 3. *Synarthonia Müll.-Arg.

Thallus with _Palmella_ gonidia.

Spores 1- or more-septate 4. Allarthonia Nyl.
Spores muriform 5. *Allarthothelium Wain.

Thallus with _Phycopeltis_ gonidia.

Spores elongate 1- or more-septate 6. *Arthoniopsis Müll.-Arg.

XIX. _GRAPHIDACEAE_

Thallus crustaceous, inconspicuous, partly immersed, mainly growing on bark but occasionally on dead wood or stone. Algal cells chiefly _Trentepohlia_, very rarely _Palmella_ or _Phycopeltis_ (epiphyllous). Apothecia (lirellae) carbonaceous more or less linear, opening by a narrow slit with a well-developed proper margin except in _Gymnographa_, a monotypic Australian genus. In two genera, the fruit is of a compound nature, several parallel discs occurring in one lirella: these are _Ptychographa_ (on bark in Scotland) and _Diplogramma_ (Australia), both are monotypic. They must not be confused with _Graphis elegans_ and allied species in which the sterile carbonaceous margin is furrowed. Two tropical genera associated with _Phycopeltis_ are epiphyllous.

Graphidaceae are among the oldest recorded lichens, attention having been drawn to them since early times by the resemblance of the lirellae on the bark of trees to hieroglyphic writing.

Thallus with _Palmella_ gonidia.

Apothecia single.
Hypothecium dark-brown.
Spores simple 1. Lithographa Nyl.
Hypothecium colourless or brownish.
Spores colourless.
Spores simple 2. Xylographa Fries.
Spores elongate 3-8-septate 3. *Aulaxina Fée.
Spores brown.
Spores 1-septate 4. Encephalographa Massal.
Spores pluri-septate, then muriform 5. *Xyloschistes Wain.
Apothecia compound.
Spores simple, colourless 6. Ptychographa Nyl.
Spores pluri-septate, colourless 7. *Diplogramma Müll.-Arg.

Thallus with _Trentepohlia_ gonidia.

Spores elongate 1-multi-septate, the cells longer than wide.
Spores brown.
Spores 1-(rarely more)-septate 8. Melaspilea Nyl.
Spores 3-septate (apothecia
rudimentary) 9. *Gymnographa Müll.-Arg.
Spores colourless.
Spores acicular, coiled (many in the
ascus) 10. *Spirographa A. Zahlbr.
Spores fusiform, straight 11. Opegrapha Humb.
Spores muriform.
Spores elongate, central cells
finally muriform 12. *Dictyographa Müll.-Arg.

Spores elongate, septate, cells wider than long.
Paraphyses unbranched, filiform.
Spores multi-septate, colourless 13. Graphis Adans.
Spores multi-septate, brown 14. Phaeographis Müll.-Arg.
Spores muriform, colourless 15. Graphina Müll.-Arg.
Spores muriform, brown 16. Phaeographina Müll.-Arg.
Paraphyses clavate, warted at tips 17. *Acanthothecium Wain.
Paraphyses branched, interwoven above 18. *Helminthocarpon Fée.

Thallus with _Phycopeltis_ gonidia (epiphyllous).

Spores elongate, 3-9-septate,
colourless 19. *Opegraphella Müll.-Arg.
Spores elongate, 1-septate, brown 20. *Micrographa Müll.-Arg.

XX. _CHIODECTONACEAE_

Specially distinguished in this subseries by the grouping of the somewhat rudimentary apothecia in pseudostromata in which they are almost wholly immersed. In form they are roundish or linear; the spores are septate or muriform. The thallus is thinly crustaceous and continuous: in _Glyphis_, _Sarcographa_ and _Sarcographina_ there is an amorphous upper cortex, the other genera are non-corticate. Algal cells are _Trentepohlia_ with the exception of two epiphyllous genera associated with _Phycopeltis_.

Genera and species are mostly tropical. _Sclerophyton_ with five species is represented in Europe by a single British specimen, _S. circumscriptum_.

The form of the paraphyses is a distinguishing character of the genera.

Thallus with _Trentepohlia_ gonidia.

Paraphyses free, unbranched.
Spore cells short or almost globose.
Spores elongate, multi-septate,
colourless 1. Glyphis Fée.
Spores elongate, multi-septate, brown 2. *Sarcographa Fée.
Spores muriform, brown 3. *Sarcographina Müll.-Arg.
Spore cells longer and cuboid.
Spores muriform, colourless 4. *Enterodictyon Müll.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate,
colourless 5. Chiodecton Ach.
Spores elongate, multi-septate, brown 6. Sclerophyton Eschw.
Spores muriform, colourless 7. *Minksia Müll.-Arg.
Spores muriform, brown 8. *Enterostigma Müll.-Arg.

Thallus with _Phycopeltis_ gonidia (epiphyllous).

Paraphyses free.
Spores unequally 2-celled,
colourless 9. *Pycnographa Müll.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate,
colourless 10. *Mazosia Massal.

XXI. _DIRINACEAE_

A small family, which is associated with and often included under Graphidaceae. The thallus is crustaceous and corticate on the upper surface, the cortex being formed of palisade hyphae. Algal cells _Trentepohlia_. Apothecia are rounded or with a tendency to elongation, and, in addition to a thin proper margin, possess a stout thalline margin; the hypothecium is thick and carbonaceous. There are two genera: _Dirina_ with twelve species has a wide distribution; _Dirinastrum_ is monotypic and occurs on maritime rocks in Australia. In both the spores are elongate-septate, differing only in colour:

Spores colourless 1. Dirina Fr.
Spores brown 2. *Dirinastrum Müll.-Arg.

XXII. _ROCCELLACEAE_

The Roccellaceae differ from the preceding Dirinaceae chiefly in the fruticose thallus which is more or less characteristic of all the genera, though in _Roccellographa_ it expands into foliose dimensions and in _Roccellina_ is reduced to short podetia-like processes from a crustose base. The fronds—mostly long and strap-shaped—are protected in most of the genera by a cortex of compact palisade hyphae; in a few the outer hyphae are parallel with the long axis. The medulla is of parallel hyphae, either loose or compact. The algal cells are _Trentepohlia_.

The apothecia are lateral except in _Roccellina_ where they occur at the tips of the short upright fronds, and only in _Roccellaria_ is there no thalline margin. They are superficial in all of the genera except _Roccellographa_, in which they are immersed and almost closed, recalling the perithecia-like fruits of _Chiodecton_ (sect. _Enterographa_). The spores are elongate, narrow, pluri-septate, and colourless or brownish, except in _Darbishirella_ in which they are ovoid, 2-septate and brown.

The affinity of Dirinaceae and Roccellaceae with Graphidaceae was first indicated by Reinke[1045] and elaborated later by Darbishire[1046] in his monograph of Roccellaceae. The apothecia in some species of _Dirina_ are ellipsoid rather than round; in several genera of Roccellaceae they are distinctly lirellate, and in _Roccella_ itself some species have ellipsoid fruits. The fruticose thallus is predominant in Roccellaceae, but its evolution from the crustaceous type may be traced through _Roccellina_ which is partly crustaceous and only imperfectly fruticose.

In most of the genera only one species is recorded. _Roccella_, represented by twelve species, is well known for its dyeing properties, and has a wide distribution. Like other Graphidineae they are mainly plants of warm regions, many of them exclusively maritime rock-dwellers.

The following synopsis of the genera is the one given by Darbishire in his monograph.

Cortex fastigate, of palisade hyphae.
Spores colourless.
Hypothecium black-carbonaceous.
Apothecia round.
Thallus fruticose 1. Roccella DC.
Thallus crustaceous-fruticose 2. *Roccellina Darbish.
Apothecia lirellate 3. *Reinkella Darbish.
Hypothecium colourless.
Gonidia present under the
hypothecium 4. *Pentagenella Darbish.
Gonidia absent from hypothecium 5. *Combea De Not.
Spores brown or brownish.
Medulla of parallel somewhat loose
hyphae 6. *Schizopelte Th. Fr.
Medulla solid, black 7. *Simonyella Steiner.
Cortex fibrous, of parallel hyphae.
Apothecia round.
Hypothecium black-carbonaceous.
Apothecia with thalline margin 8. *Dendrographa Darbish.
Apothecia with proper margin 9. *Roccellaria Darbish.
Hypothecium colourless 10. *Darbishirella A. Zahlbr.
Apothecia lirellate 11. *Ingaderia Darbish.

SUBSERIES 3. =Cyclocarpineae=

This last subseries includes the remaining twenty-nine families of Ascolichens. They are very varied both in the fungal and the algal symbionts. The fruit is more or less a discoid open apothecium. The gonidia belong to different genera of Myxophyceae and Chlorophyceae, but the most frequent are Protococcaceae. Families are based largely on thalline structure.

XXIII. _LECANACTIDACEAE_

By many systematists this family is included under Graphidineae on account of the fruit structure which in some of the forms is carbonaceous and almost lirellate, and also because the algal symbiont is _Trentepohlia_. The thallus is primitive, being thinly crustaceous and non-corticate; the apothecium has a black carbonaceous hypothecium in two of the genera, _Lecanactis_ and _Schismatomma_ (_Platygrapha_); in the third genus, _Melampydium_, it is colourless. The latter is monotypic, and the spores become muriform. In the other genera they are elongate and multi-septate.

Apothecia with prominent proper margin 1. Lecanactis Eschw.
Apothecia with thin proper margin 2. *Melampydium Müll.-Arg.
Apothecia with thalline margin 3. Schismatomma Flot.

XXIV. _PILOCARPACEAE_

A small family with but one genus, _Pilocarpon_. It is distinguished as one of the few epiphyllous genera of lichens associated with Protococcaceous gonidia and with a distribution extending far beyond the tropics. The best known species, _P. leucoblepharum_, encircles the base of pine-needles with a white felted crust, or inhabits coriaceous evergreen leaves. Another species lives on fern leaves. The fruit is a discoid apothecium with a dark carbonaceous hypothecium and proper margin, and with a second thalline margin. The paraphyses are branched and interwoven above.

Spores elongate, 3-septate, colourless 1. Pilocarpon Wain.

XXV. _CHRYSOTRICHACEAE_

This family now, according to Hue[1047], includes two genera, _Crocynia_ and _Chrysothrix_. In both there is a thallus of interlaced hyphae with Protococcaceous algae scattered through it or in groups. The structure is thus homoiomerous, and Hue has suggested for it a new series, “Intertextae.” The only British species, _Crocynia lanuginosa_, first placed by Nylander[1048] in _Amphiloma_ and later transferred by him to _Leproloma_[1049], has a soft crustaceous lobate thallus, furfuraceous on the surface; no fructification has been found. A West Indian species, _C. gossypina_, has discoid apothecia with a thalline margin. There is only one species of _Chrysothrix_, _Ch. nolitangere_, which forms small clumps or tufts on the spines of Cactus in Chili. The structure is somewhat similar to that of _Crocynia_.

Spores colourless, simple 1. Crocynia Nyl.
Spores colourless, 2-3-septate 2. *Chrysothrix Mont.

XXVI. _THELOTREMACEAE_

A tropical or subtropical family of which the leading characteristic is the deeply sunk disc of the apothecium: it has a proper hyphal margin, and, round that, an overarching thalline margin. The apothecia occur singly, or they are united in a kind of pseudostroma: in _Tremotylium_ several grow together, while in _Polystroma_ each new apothecium develops as an outgrowth from the thalline margin of the one already formed, so that an upright, branching succession of fruits is built up. It is a very unusual type of lichen fructification, with one species, _P. Ferdinandezii_, found in Spain and in Guiana.

The thallus in all the genera is crustaceous with an amorphous (decomposed) cortex; or it is non-corticate. The algal cells are _Trentepohlia_ except in _Phyllophthalmaria_, an epiphyllous genus associated with the alga _Phycopeltis_. In _Polystroma_ the alga is unknown.

Only one genus is represented in the British Isles.

Apothecia growing singly.
Thallus with _Trentepohlia_ gonidia.
Paraphyses numerous, unbranched, free.
Spores colourless.
Spores elongate, 2- or
multi-septate 1. *Ocellularia Spreng.
Spores muriform 2. Thelotrema Ach.
Spores brown.
Spores elongate, septate 3. *Phaeotrema Müll.-Arg.
Spores muriform 4. *Leptotrema Mont.
Paraphyses scanty, branched.
Spores muriform, brown 5. *Gyrostomum Fr.
Thallus with _Phycopeltis_ gonidia 6. *Phyllophthalmaria A.
Zahlbr.
Apothecia in pseudostromata.
Apothecia united in tubercles 7. *Tremotylium Nyl.
Apothecia united by the margins 8. *Polystroma Clem.

XXVII. _DIPLOSCHISTACEAE_

Scarcely differing from the preceding family except in the gonidia which are Protococcaceous algae. The thallus is crustaceous and non-corticate. The apothecia have a double margin but the outer thalline margin is less overarching than in Thelotremaceae. The spores in the two genera are somewhat peculiar: in _Conotrema_ they are exceedingly long and divided by parallel septa into thirty to forty small cells; in _Diploschistes_ (_Urceolaria_) they are large, muriform and brown. _Conotrema_ contains two corticolous species; _Diploschistes_ about thirty species mostly saxicolous. Both genera are represented in the British Isles.

Spores elongate, multi-septate,
colourless 1. Conotrema Tuck.
Spores muriform, brown 2. Diploschistes Norm.

XXVIII. _ECTOLECHIACEAE_

A family of tropical epiphyllous lichens that are associated with Protococcaceous gonidia. The thallus is primitive in character, mostly a weft of hyphae with intermingled algal cells, described as homoiomerous.

The apothecia are without a thalline margin, and with a scarcely developed proper margin: their affinity is with the Lecideaceae, though in two genera, _Lecaniella_ and _Arthotheliopsis_, there are gonidia below the hypothecium, a character of Lecanoraceae. The genera are nearly all monotypic; in _Sporopodium_ has been included _Lecidea phyllocharis_ Wainio (Sect. _Gonothecium_), which is distinguished by hymenial gonidia.

Apothecia at first covered by a “veil.”
Spores elongate, colourless,
septate 1. *Asterothyrium Müll.-Arg.
Apothecia uncovered from the first.
Gonidia not present below the hypothecium.
Paraphyses unbranched, free.
Spores muriform 2. *Lopadiopsis Wain.
Paraphyses branched.
Spores 1-septate 3. *Actinoplaca Müll.-Arg.
Spores elongate, multi-septate 4. *Tapellaria Müll.-Arg.
Spores muriform 5. *Sporopodium Mont.
Gonidia present below the hypothecium.
Spores elongate, 2-septate 6. *Lecaniella Wain.
Spores muriform 7. *Arthotheliopsis Wain.

XXIX. _GYALECTACEAE_

The algal cells in this family are filamentous; either Myxophyceae (_Scytonema_) or Chlorophyceae (_Trentepohlia_ or _Phyllactidium_). The thallus is crustaceous, and in some cases homoiomerous, as in _Petractis_, where the alga, _Scytonema_, penetrates the substratum as deeply as the hyphae. _Monophiale_, a tropical genus, possesses two kinds of gonidia: the species that grow on bark or mosses are associated with _Trentepohlia_; others that have invaded the surface of leathery evergreen leaves resemble most epiphyllous lichens in being associated with the leaf alga _Phyllactidium_ (_Phycopeltis_). Some species of _Trentepohlia_ exhale when moist an odour of violets. This scent is retained in at least one genus, _Jonaspis_.

The apothecia are superficial, and are soft, waxy and bright-coloured, with prominent margins which are however entirely hyphal: the affinity is therefore with Lecideaceae. In one genus, _Sagiolechia_, the fruit is carbonaceous and dark coloured. The spores of all the genera are colourless.

Apothecia waxy, bright-coloured.
Thallus with _Scytonema_ gonidia.
Spores elongate, 3-septate 1. Petractis Fr.
Thallus with _Trentepholia_ gonidia.
Asci 6-8-spored.
Spores simple 2. Jonaspis Th. Fr.
Spores 1-septate 3. *Microphiale A. Zahlbr.
Spores septate or muriform 4. Gyalecta Ach.
Asci 12-many-spored.
Spores 1-septate 5. *Ramonia Stizenb.
Spores fusiform or acicular,
many-septate 6. Pachyphiale Lönnr.
Apothecia carbonaceous.
Spores elongate, 2-3-septate 7. *Sagiolechia Massal.

XXX. _COENOGONIACEAE_

There are only two genera in this small family, _Coenogonium_ with _Trentepohlia_ gonidia, and _Racodium_ with _Cladophora_. Both genera follow the algal form and are filamentous. In _Coenogonium_ the filaments are sometimes matted into a loose felted expansion. The genus is mainly tropical or subtropical and mostly rather light-coloured. There is only one British species, _C. ebeneum_[1050], a sterile form, in which the hyphae are very dark-brown; it often covers large areas of stone or rock with its sooty-like creeping filaments.

_Racodium_ includes 2 (?) species. One of these, _R. rupestre_, is sterile and resembles _C. ebeneum_ in form and colour.

The apothecia of _Coenogonium_ are waxy and light-coloured; they are borne laterally on the filaments; the spores are simple or 1-septate.

Thallus with _Trentepohlia_ gonidia 1. Coenogonium Ehrenb.
Thallus with _Cladophora_ gonidia 2. Racodium Fr.

XXXI. _LECIDEACEAE_

One of the largest lichen families as regards both genera and species, and of world-wide distribution. The algal cells are Protococcaceae. The thallus is mostly crustaceous but it becomes squamulose in _Psora_, a section of _Lecidea_; and in _Sphaerophoropsis_, a Brazilian genus, there are small upright fronds or stalks with lateral apothecia. The prevailing colour of the thallus is some shade of grey, but it ranges from white or yellow to dark-brown or almost black. Cephalodia appear in some of the species.

The apothecia have a proper margin only, no gonidia taking part in the fruit-formation. They may be soft and waxy (biatorine) or hard and carbonaceous (lecideine). The genera are mainly based on spore characters which are very varied.

The arrangement of genera given below follows that of Zahlbruckner; in several instances, both as to the limitations of genera and to the nomenclature, it differs from that of British text-books, though the general principle of classification is the same.

Thallus crustaceous non-corticate.
Spores simple.
Spores small, thin-walled.
Spores colourless 1. Lecidea Ach.
Spores brown 2. *Orphniospora Koerb.
Spores large, thick-walled 3. Mycoblastus Norm.
Spores 1-septate.
Spores small, thin-walled 4. Catillaria Th. Fr.
Spores large, thick-walled 5. Megalospora Mey. and Flot.
Spores elongate, 3-multi-septate.
Spores elongate, narrow, thin-walled 6. Bacidia A. Zahlbr.
Spores elongate, large and
thick-walled 7. Bombyliospora De Not.
Spores muriform.
Spores colourless; on trees 8. Lopadium Koerb.
Spores colourless to brown; on rocks 9. Rhizocarpon Th. Kr.
Thallus warted or squamulose, corticate.
Spores elongate, 1-7-septate,
thin-walled 10. Toninia Th. Fr.
Thallus of upright podetia-like small fronds.
Spores ellipsoid, becoming 1-septate 11. *Sphaerophoropsis Wain.

XXXII. _PHYLLOPSORACEAE_

A small family of exotic lichens with a somewhat more developed thallus than that of the Lecideaceae, being in both of the genera squamulose or almost foliose.

The apothecia are without a thalline margin; they are biatorine or lecideine; the hypothecium is formed of plectenchyma and is purple-red in one species, _Phyllopsora furfuracca_. The two genera differ only in spore characters. There are fifteen species, mostly corticolous, belonging to _Phyllopsora_; only one, from New Zealand, is recorded for _Psorella_.

Spores simple 1. *Phyllopsora Müll.-Arg.
Spores elongate, septate 2. *Psorella Müll.-Arg.

XXXIII. _CLADONIACEAE_

Associated with Lecideaceae in the type of apothecium, but differing widely in thallus formation. The latter is of a twofold type: the primary thallus is crustaceous, squamulose, or very rarely foliose; the secondary thallus or podetium, upright, simple or branched, is terminated by the apothecia, or broadens upwards to cup-like scyphi. Algal cells, Protococcaceae, according to Chodat, _Cystococcus_.

Much attention has been given to the origin and development of the podetia in this family. They are superficial on granule or squamule except in the monotypic Himalayan genus _Gymnoderma_ where they are marginal on the large leaf-like lobes. Though in origin the podetia are doubtless fruit stalks, they have become in most cases vegetative in function.

The fruits are coloured yellowish, brown or red (or dark and carbonaceous in _Pilophorus_), and are borne on the tips of the branches or on the margins of the scyphi. In _Glossodium_ and _Thysanothecium_—the former from New Granada, the latter from Australia—the apothecia occupy one side of the widened surface at the tips.

Cephalodia are developed on the primary thallus of _Pilophorus_, and on the podetia of _Stereocaulon_ and _Argopsis_.