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.
| Algal cells Scytonema. | ||
| Thallus minutely fruticose, non-corticate | 1. | Thermutis Fr. |
| Thallus minute, of felted filaments, | ||
| cortex one cell thick | 2. | *Leptodendriscum Wain. |
| Thallus of elongate filaments, cortex of | ||
| several cells | 3. | Leptogidium Nyl. |
| Thallus foliose or fruticose, | ||
| cellular throughout | 4. | Polychidium Ach. |
| Thallus crustaceous, non-corticate | 5. | Porocyphus Koerb. |
| Algal cells Stigonema. | ||
| Thallus minutely fruticose, non-corticate | 6. | Spilonema Born. |
| Thallus of long branching filaments. | ||
| Spores septate; paraphyses wanting | 7. | Ephebe Fr. |
| Spores simple; paraphyses present | 8. | Ephebeia Nyl. |
| Thallus crustaceous; upper surface | ||
| non-corticate, lower surface corticate | 9. | *Pterygiopsis Wain. |
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.
| Thallus with Gloeocapsa gonidia. | ||
| Thallus crustaceous. | ||
| Spores simple | 1. | Pyrenopsis Nyl. |
| Spores 1-septate | 2. | *Cryptothele Forss. |
| Thallus shortly fruticose | 3. | Synalissa Fr. |
| Thallus lobate, centrally attached | 4. | *Phylliscidium Forss. |
| Thallus with Chroococcus gonidia. | ||
| Thallus crustaceous | 5. | Pyrenopsidium Forss. |
| Thallus lobate, centrally attached | 6. | *Phylliscum Nyl. |
| Thallus with Xanthocapsa gonidia. | ||
| Thallus crustaceous. | ||
| Thallus non-corticate. | ||
| Spores simple. | ||
| Apothecia open, asci 8-spored | 7. | Psorotichia Forss. |
| Apothecia covered, asci many-spored | 8. | *Gonohymenia Stein. |
| Spores 1-septate. | ||
| Apothecia closed | 9. | *Collemopsidium Nyl. |
| Thallus with plectenchymatous cortex | 10. | *Forssellia A. Zahlbr. |
| Thallus lobate, centrally attached. | ||
| Spores simple. | ||
| Thallus plectenchymatous throughout | 11. | *Anema Nyl. |
| Thalline tissue of loose hyphae | 12. | *Thyrea Massal. |
| Cortex of upright parallel hyphae | 13. | *Jenmania Wächt. |
| Spores 1-septate. | ||
| Thalline tissue of loose hyphae | 14. | *Paulia Fée. |
| Thallus fruticose. | ||
| Thallus without a cortex | 15. | *Peccania Forss. |
| Thallus with cortex of parallel hyphae | 16. | *Phloeopeccania Stein. |
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.