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:

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:

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:

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.

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.

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.

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.

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.

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.

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.

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.

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:

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

XXXIV. Gyrophoraceae

A small family of foliose lichens allied to Lecideaceae by the character of the fruit—a superficial apothecium in the formation of which the gonidia take no share. There are only three genera, distinguished by differences in spore and other characters. Dermatiscum has light-coloured thallus and fruits; of the two species, one occurs in Central Europe, the other in North America. Umbilicaria and Gyrophora are British; they are dark-coloured rock-lichens and are extremely abundant in Northern regions where they are known as “tripe de roche.” Algal cells Protococcaceae.

Umbilicaria, Dermatiscum, and some species of Gyrophora are attached to the substratum by a central point. Other species of Gyrophora are rhizinose. In all there is a cortex of plectenchyma above and below. In Gyrophora the thallus may be monophyllous as in Umbilicaria, or polyphyllous and with or without rhizinae. New lobes frequently arise from protuberances or warts on the older parts of the thallus. At the periphery, in most species, growth is equal along the margins, in G. erosa[1052] the edge is formed of numerous anastomosing lobes with lateral branching, the whole forming a broadly meshed open network. Further back the tissues become continuous owing to the active growth of the lower tissue or hypothallus, which grows out from all sides and meets across the opening. The overlying layers, with gonidia, follow more slowly, but they also in time become continuous, so that the “erose” character persists only near the periphery. This forward growth of the lower thallus occurs in other species, though to a much less marked degree.

There is abundant detritus formation in this family; the outer layers of the cortex are continually being sloughed, the dead tissues lying on the upper surface as a dark gelatinous layer, continuous or in small patches. On the under surface the cast-off cortex gathers into a loose confused mass of dead tissues.

XXXV. Acarosporaceae

Thallus foliose, squamulose or crustaceous, sometimes scarcely developed. Algal cells Protococcaceae.

Into this family Zahlbruckner has gathered the genera in which the asci are many-spored, as he considers that a character of great importance in determining relationship, but he has in doing so overlooked other very great differences. The fruit-bodies are round and completely enclosed in a thalline wall in Thelocarpon, which has however no perithecial wall. They have a proper margin only (lecideine) in Biatorella, and a thalline margin (lecanorine) in the remaining genera. In Acarospora the apothecia are sunk in the thallus. Stirton’s genus Cryptothecia[1053] is allied to Thelocarpon in the fruit-formation, but the basal thallus is well developed and the spores are few in number and variously divided.

XXXVI. Ephebaceae

A family of very simple structure either filamentous, foliose or crustaceous. The algal cells which give a dark colour to the thallus are Stigonema or Scytonema, members of the blue-green Myxophyceae, and consist of minute simple or branched filaments—single cell-rows in Scytonema, compound in Stigonema.

In some of the genera the lichen hyphae travel within the gelatinous sheath of the filaments, both algae and hyphae increasing by apical growth so that filaments many times the length of the alga are formed as in Ephebe. In others the filaments scarcely increase beyond the normal size of the alga as in Thermutis (Gonionema); or the gelatinous algal cells may be distributed in a stratum of hyphae.

The apothecia are minute and almost closed; they may be embedded in swellings of the thallus, or are more or less superficial. The spores are rather small, colourless and simple or 1-septate.

The lichens of this family are rock-dwellers and are mostly to be found in hilly or Alpine regions. A tropical species, Leptogidium dendriscum, occurs in sterile condition in south-west Ireland. There are few species in any of the genera.

XXXVII. Pyrenopsidaceae

In this family are included gelatinous lichens of which the gonidium is a blue-green alga with a thick gelatinous coat, either Gloeocapsa (including Xanthocapsa) or Chroococcus. In Gloeocapsa and Chroococcus the gelatinous envelope is often red, in Xanthocapsa it is yellow, and these colours persist more or less in the lichens, especially in the outer layers.

The thallus is in many cases a formless gelatinous crust of hyphal filaments mingling with colonies of algal cells as in Pyrenopsis; but small fruticose tufts are characteristic of Synalissa, and larger foliose and fruticose thalli appear in some exotic genera. A plectenchymatous cortex is formed on the thallus of Forssellia, a crustaceous genus from Central Europe, with two species only; the whole thallus is built up of a kind of plectenchyma in some others, but in most of the genera there is no tissue formed.

The apothecia, as in Ephebaceae, are generally half-closed.

XXXVIII. Lichinaceae

The only family of lichens associated with Rivularia gonidia, the trichomes of which retain their filamentous form to some extent in the more highly developed genera; they lie parallel to the long axis of the squamule or of the frond except in Lichinella in which genus they are vertical to the surface. The thallus may be crustaceous, or minutely foliose, or fruticose; in all cases it is dark-brown in colour, and the gelatinous character is evident in the moist condition. The best known British genus is Lichina which grows on rocks by the sea.

The apothecia are more or less immersed in the tissue; in Pterygium and Steinera they are open and superficial (the latter monotypic genus confined to Kerguelen). They are also open in Lichinella and Homopsella, both very rare genera. The spores are colourless and simple except in Pterygium and Steinera where they are elongate, and 1-3-septate.

XXXIX. Collemaceae

The most important family of the gelatinous lichens and the most numerous. Collema is historically interesting as having first suggested the composite thallus. Algal cells, Nostoc, which retain the chain-like form except in Leprocollema, a doubtful member of the family. The thallus varies from indeterminate crusts to lobes of considerable size; occasionally the lobes are narrow and erect, forming minute fruticose structures. In the more primitive genera the thallus is non-corticate, but in the more evolved, the apical cells of the hyphae coalesce to form a continuous cellular cortex, one or more cells thick, well marked in some species, in others rudimentary; the formation of plectenchyma also occurs occasionally in the apothecial tissues of some non-corticate species.

The apothecia are superficial except in Pyrenocollema, a monotypic genus of unknown locality. They are generally lecanorine, with gonidia entering into the formation of the apothecium: in some genera they are lecideine or biatorine, being formed of hyphae alone. The spores are colourless and vary in form, size and septation.

XL. Heppiaceae

A family belonging to the “blue-green” series as it is associated with a gelatinous alga, Scytonema, but is of almost entirely cellular structure and is non-gelatinous. The thallus is squamulose or minutely foliose, or is formed of narrow almost fruticose lobes; the apothecia are semi-immersed; the asci are 4-many-spored.

Heppia is a wide-spread genus both in northern and tropical regions with about forty species that live on soil or rock. So far, no representative has been recorded in our Islands.

XLI. Pannariaceae

The members of this family are also non-gelatinous, though for the most part associated with blue-green gelatinous algae, Nostoc or Scytonema. The gonidia are bright-green in the genera Psoroma and Psoromaria, the former often included under Lecanora, but too closely resembling Pannaria to be dissociated from that genus.

The thallus varies from being crustaceous to squamulose or foliose, and has a cortex of plectenchyma on the upper and sometimes also on the lower surface. The apothecia are superficial or lateral and with or without a thalline margin (lecanorine or biatorine), the spores are colourless.

Zahlbruckner has included Hydrothyria in this family. It is a monotypic aquatic genus found in North America and very closely allied to Peltigera. The British species of the genus, familiarly known as Coccocarpia, have been placed under Parmeliella, the former name being restricted to the tropical or subtropical species first assigned to Coccocarpia and distinguished by the cortex, the hyphae forming it lying parallel with the surface though forming a regular plectenchyma.

An Antarctic lichen Thelidea corrugata with Palmella gonidia is doubtfully included: the thallus is foliose, the apothecia biatorine with colourless 1-septate spores.

XLII. Stictaceae

Thallus foliose, mostly horizontal, with a plectenchymatous cortex on both surfaces, a tomentum of hair-like hyphae taking the place of rhizinae on the lower surface. Algal cells Protococcaceae or Nostoc. Cephalodia and cyphellae or pseudocyphellae often present. Apothecia superficial or lateral; spores colourless or brown, variously septate.

The highly organized cortex and the presence of aeration organs—cyphellae or pseudocyphellae—which are almost solely confined to the genus Sticta give this family a high position as regards vegetative development. The two genera are of wide distribution, but Sticta is more abundant in the Southern Hemisphere. Lobaria pulmonaria is one of our largest lichens.

XLIII. Peltigeraceae

A family of heteromerous foliose lichens containing in some instances blue-green (Nostoc), in others bright-green (Protococcaceae) gonidia, and thus representing a transition between these two series. They have large or small lobes and grow on the ground or on trees.

Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina), occur in the family and further exemplify the capacity of the fungus hyphae to combine with different types of algae.

The upper surface is a wide cortex of plectenchyma, which in some forms (Nephromium) is continued below. In the non-corticate under surface of Peltigera, the lower hyphae grow out in hairs or rhizinae, very frequently brown in colour. Intercalary growth of the upper tissues stretches the thallus and tears apart the lower under surface so that the hair-bearing areas become a network of veins, with the white exposed medulla between. In Peltigera canina there is further growth and branching of the hyphae in the veins, adding to the bulk of the interlacing ridges.

From all other foliose lichens Peltigeraceae are distinguished by the flat wholly appressed or peltate apothecia without a thalline margin which arise mostly on the upper surface, but in Nephromium on the extreme margin of the under surface, the tip of the fertile lobe in that case is turned back as the apothecium matures, so that the fruit eventually faces the light. In Nephroma has been included Eunephroma with bright-green gonidia and Nephromium with blue-green.

Bitter[1055] has recorded the finding of apothecia on the under surface of Peltigera malacea and not at the margin, as in Nephromium. The plant was otherwise normal and healthy. Solorinella, from Central Europe and Asteristion from Ceylon are monotypic genera with poorly developed thalli.

XLIV. Pertusariaceae

Thallus crustaceous, often rather thick and with an amorphous cortex on the upper surface. Algal cells Protococcaceae. Apothecia solitary or several immersed in thalline warts, generally with a narrow opening which barely exposes the disc, and which in one genus, Perforaria, is so small as almost to constitute a perithecium; spores are often very large and with thick walls; some if not all are multinucleate and germinate at many points.

In the form of the fruit, this family stands between Pyrenocarpeae and Gymnocarpeae, though more akin to the latter. Perforaria, with two species, belongs to New Zealand and Japan. Pertusaria has a world-wide distribution, and Varicellaria, a monotypic genus, with a very large two-celled spore, is an Alpine plant, recorded from Europe and from Antarctic America.

XLV. Lecanoraceae