Monographs Details: Riccia plano-biconvexa Steph.
Authority: Bischler, Hélène, et al. 2005. Marchantiidae. Fl. Neotrop. Monogr. 97: 1--262. (Published by NYBG Press)
Synonyms:Riccia tenuilimbata Steph.
Description:Species Description - Thalli in gregarious patches; lobes 7-12 mm long, 1.5-2.3(-3) mm wide, thin, rounded or slightly emarginate apically; dorsal side light green or greenish with hyaline, margins 3-4 cells wide; flanks and ventral side light green, or brownish, or violaceous. Median groove distinct apically, flattened and vanishing toward base. Epidermal cells disintegrating. Ventral scales hyaline, usually not extending beyond lobe margins. Cross section of lobes 3-5 times as wide as high; dorsal edge abruptly extending into thin wings 3-4 cells high, ending in a hyaline cell; flanks erect; ventral edge convex; dorsal tissue in 8-10 cell layers, thinner than ventral tissue, all cells thin-walled. Dioecious? Archegonial necks protruding, violet basally, hyaline above. Spores subspherical, 70-90 or 100-130 µm diam., red-brown, wingless; distal face with 8-11 areoles across diam., those of central part smaller (7-8 µm diam.) than those of periphery (914 µm diam.), with thin, high ridges and thin tubercles 6 µm high; proximal face similarly ornamented, with somewhat lower ridges and tubercles, triradiate scar indistinct.

Discussion:Riccia subplana is related to R. plano-biconvexa, but the spores of the former species are pink-violet or red-violet, with only 4-6 areoles across diam, of the distal face.

Hassel de Menéndez (1963) included/?, weinionis and R. corcovadensis as synonyms in Riccia planobiconvexa. However, the former 2 taxa have 2 thickened strips in the cells of the dorsal tissue, a character not seen in R. plano-biconvexa.

Distribition and Ecology: Riccia plano-biconvexa is a neotropical species recorded from Costa Rica (Jovet-Ast, 1981), the Galapagos Islands (Isabela (Gradstein & Weber, 1982)), Brazil (Alagoas, Bahía, Espíritu Santo, Goiás, Mato Grosso, Pernambuco, Rio Grande do Norte, Rio Grande do Sul), Paraguay, and Argentina (Misiones (Herzog, 1952)). It seems to be quite common in Brazil and has been collected on sandy, granitic or clayey soil, on soil over rocks, exposed on seasonal riverbanks, on borders of ponds, in pastures, between paving stones in towns, or sheltered by open vegetation, in caatinga or gardens, from sea level to 500 m.

Distribution:Goiás Brazil South America| Mato Grosso Brazil South America| Alagoas Brazil South America| Bahia Brazil South America| Pernambuco Brazil South America| Rio Grande do Sul Brazil South America| Rio Grande do Norte Brazil South America| Espirito Santo Brazil South America| Paraguay South America|