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.
| Apothecia immersed; spores fusiform, 1-septate | 1. | *Pyrenocollema Reinke. |
| Apothecia superficial. | ||
| Thallus without a cortex. | ||
| Spores simple, globose or ellipsoid. | ||
| Thallus crustaceous | 2. | *Leprocollema Wain. |
| Thallus largely squamulose-fruticose. | ||
| Apothecia lecideine (dark-coloured) | 3. | *Leciophysma Th. Fr. |
| Apothecia lecanorine | 4. | Physma Massal. |
| Spores variously septate or muriform. | ||
| Apothecia biatorine (light-coloured) | 5. | *Homothecium Mont. |
| Apothecia lecanorine | 6. | Collema Wigg. |
| Thallus with cortex of plectenchyma. | ||
| Spores simple. | ||
| Spores globose | 7. | Lemmopsis A. Zahlbr. |
| Spores ellipsoid, with thick subverrucose wall | 8. | *Dichodium Nyl. |
| Spores vermiform, spirally curved | 9. | *Koerberia Massal. |
| Spores variously septate or muriform. | ||
| Apothecia biatorine (light-coloured) | 10. | *Arctomia Th. Fr. |
| Apothecia lecanorine | 11. | Leptogium S. F. Gray. |
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.