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.
| Thallus with Trentepohlia gonidia | 1. | Coenogonium Ehrenb. |
| Thallus with Cladophora gonidia | 2. | Racodium Fr. |