1. RÍCCIA, Micheli. ([Pl. 22.])
Thallus at first radiately divided, the centre often soon decaying; the divisions bifid or di–tri-chotomous, flat or depressed or channelled above, usually convex and naked or squamulose beneath; margins naked or spinulose-ciliate; epidermis usually distinct, eporose; air-cavities evident or wanting. Capsule immersed, sessile. Calyptra with a persistent style. Spores alveolate or muriculate, usually flattened and angular. (Named for P. F. Ricci, an Italian nobleman, patron of Micheli.)
§ 1. LICHENÒDES. Fruit mostly protuberant above; spores about 84 µ broad, issuing through openings in the upper surface of the thallus; terrestrial species (on damp, usually trodden or cultivated ground), without air-cavities.
[*] Thallus naked, without cilia or scales.
1. R. Fróstii, Aust. Thallus orbicular, 6–12´´ broad, thinnish, grayish-green, the apex and narrowly membranous margins sometimes purplish, minutely pitted; divisions linear or subspatulate, subtruncate and slightly emarginate; rootlets smooth or obsoletely papillose within; capsules very prominent beneath; spores barely 50 µ broad, nearly round, somewhat margined, with depressed sides when dry, fuscous.—Ohio, Ill., and westward.
[*][*] Thallus with white scales beneath (dark purple in n. 4), the margin naked.
2. R. sorocárpa, Bisch. Thallus 3–8´´ in diameter, pale green becoming whitish, finely reticulate, subradiately or dichotomously divided, the oblong-linear segments subacute, deeply sulcate, with a few inconspicuous scales toward the apex not extending beyond the margin; margins erect when dry; spores issuing through chinks early appearing along the groove above.—Thin rocky soil and cultivated fields, Closter, N. J. (Austin), western N. Y. (Clinton), and Ill. (Hall). (Eu.)
3. R. lamellòsa, Raddi. Thallus pale green, elegantly reticulated, subradiately divided, the divisions obovate or obcordate, bifid or 2-lobed, 2–5´´ long, channelled at the apex, with membranous ascending margins, and furnished beneath with transverse scales which extend considerably beyond the margin; spores much as in n. 2.—Thin rocky soil, Closter, N. J. (Austin).
4. R. nigrélla, DC. Thallus dichotomously divided, the divisions linear, channelled, with entire narrowly membranous margins, green above, dark purple beneath and furnished with transverse semicircular scales not exceeding the margin.—Rocky ground, N. Y. (Torrey), and Chester, Penn. (Porter). (Eu.)
[*][*][*] Thallus more or less ciliate, naked beneath or obsoletely squamous along the extreme edge.