| Thallus strap-shaped. | ||
| Structure dorsiventral. | ||
| Greyish-green above | 1. | Evernia Ach. |
| Whitish-yellow above | 2. | *Everniopsis Nyl. |
| Structure radiate alike on both surfaces. | ||
| Fronds grey; medulla of loose hyphae | 3. | Ramalina Ach. |
| Fronds yellow; medulla traversed by strands | 4. | *Letharia A. Zahlbr. |
| Thallus filamentous. | ||
| Medulla a strong “chondroid” strand | 5. | Usnea Dill. |
| Medulla of loose hyphae. | ||
| Spores simple | 6. | Alectoria Ach. |
| Spores muriform, brown | 7. | *Oropogon Fr. |
| Thallus of upright podetia-like fronds. | ||
| Fronds rather long (about two inches), tapering, white | 8. | Thamnolia Ach. (Cerania S. F. Gray). |
| Fronds shorter, blunt. | ||
| Medulla solid | 9. | *Siphula Fr. |
| Medulla partly or entirely hollow. | ||
| Fronds swollen and tall (about two inches) | 10. | *Dactylina Nyl. |
| Fronds coralloid, entangled | 11. | *Endocena Cromb. |
| Fronds short, upright | 12. | *Dufourea Nyl. |
XLVIII. Caloplacaceae
In this family Zahlbruckner has included the squamulose or crustaceous lichens with colourless polarilocular spores, relegating those with more highly developed thallus or with brown spores to other families. He has also substituted the name Caloplaca for the older Placodium, the latter being, as he considers, less well defined.
Algal cells are Protococcaceae. The thallus is mostly light-coloured, generally some shade of yellow, and, with few exceptions, contains parietin, which gives a purple colour on the application of potash. The squamulose forms are closely appressed to the substratum, and have often a definite rounded outline (effigurate). The spores have a thick median septum with a loculus at each end and a connecting canal[1059].
In Blastenia the outer thalline margin is obscure or absent—though gonidia are frequently present below the hymenium. Caloplacaceae occur all over the globe; they are among the most brilliantly coloured of all lichens. Polycauliona Hue[1060] possibly belongs here: though based on thalline rather than on spore characters, one species at least has polarilocular spores.
| Apothecia with a distinct thalline margin | 1. | Caloplaca Th. Fr. |
| Apothecia without a thalline margin | 2. | Blastenia Th. Fr. |
XLIX. Teloschistaceae
Polarilocular colourless spores are the distinguishing feature of this family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus of Teloschistaceae is more highly developed, being either foliose or fruticose, though never attaining to very large dimensions. The cortex of Xanthoria (foliose) is plectenchymatous, that of Teloschistes (fruticose) is fibrous. The species of both genera are yellow or greenish-yellow due to the presence of the lichen-acid parietin.