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.

Podetia simple, short, not widening upwards.
Podetial stalks naked.
Primary thallus thin, continuous1.Gomphillus Nyl.
Primary thallus granular or squamulose2.Baeomyces Pers.
Primary thallus foliose.
Podetia superficial3.*Heteromyces Müll.-Arg.
Podetia marginal4.*Gymnoderma[1051] Nyl.
Podetial stalks granular, squamulose5.Pilophorus Th. Fr.
Podetia short, widening upwards.
Podetia simple above, rarely divided6.*Glossodium Nyl.
Podetia lobed, leaf-like7.*Thysanothecium Berk. & Mont.
Podetia elongate, variously branched, or scyphous and hollow8.Cladonia Hill.
Podetia elongate, not scyphous, the stalks solid.
Spores elongate, septate9.Stereocaulon Schreb.
Spores muriform10.*Argopsis Th. Fr.
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.