Monographs Details: Riccia cavernosa Hoffm.
Authority: Bischler, Hélène, et al. 2005. Marchantiidae. Fl. Neotrop. Monogr. 97: 1--262. (Published by NYBG Press)
Scientific Name:Riccia cavernosa Hoffm.
Synonyms:Riccia brandegei Underw., Riccia catalinae Underw., Riccia montagnei Steph.
Description:Species Description - Thalli in rosettes of 35 mm diam., spongy, deeply divided to 3-8 mm, or in gregarious patches; lobes narrow, 1-2(-3) mm wide, rounded or emarginate apically; dorsal side green or yellow-green when dry, sometimes tinged with pink on margins and above sporangia. Median groove indistinct. Epidermis often disintegrating. Pores small at apex, larger and numerous in older parts of lobes, 20-40 µm diam., bounded by 4(-5) cells. Ventral scales absent. Cross section of lobes 3-5 times as wide as high, not narrowed into lateral wing; air chambers in 2-4 layers, 2/3-3/4 of lobe height. Monoecious. Antheridial necks colorless, hardly protruding. Archegonial necks pink violaceous, hardly protruding. Sporangia black, mainly bulging ventrally. Spores tetrahedral, 150-300 per sporangium, red-brown or black-brown, 60-120 µm diam.; wing 3.5-6 µm wide, light red-brown, papillose, complete or locally narrowed and becoming evanescent, sometimes weakly thickened at margin; distal face with dark red-brown ridges, irregularly crenulate, with complete areoles at periphery or with a branched net, delimiting 4 squares at the pole, with central short ridge or tubercle, or drawing a Y or an X; proximal face with incomplete areoles or with short and distant ridges, or with tubercles mixed with short ridges, triradiate scar well marked. Gametophytic chromosome number n = 8.

Discussion:The spore wall ornamentation in R. cavernosa is quite variable. The polar region of the distal face shows thickenings forming an X or a Y; sometimes, the branches of the X and the Y extend toward the ridges of the marginal areoles and draw 3-4 central areoles with some tubercles and ridge fragments in the center, especially in Argentinean specimens. The ornamentation of the proximal face also varies, from complete areoles with thick ridges to individual, incurved, sinuose, and branched ridges. Riccia cavernosa might comprise allopatric variants.

Schuster (1992b) treated Riccia bahiensis as a synonym of R. cavernosa.

Distribution and Ecology: Riccia cavernosa is widely distributed in C Europe to Scandinavia, in the Mediterranean area, Macaronesia (Canary Islands), Africa (Ethiopia, Cameroon, Zaire, E Africa, S Africa), Asia (SW Asia, Siberia, Mongolia), and Australia. It has been recorded from the U.S.A. (25 states) and the Neotropics: Mexico (Baja California (Underwood, 1894), Querétaro), Bahamas (Evans, 1911), Ecuador (Cotopaxi), Peru (Cajamarca, La Libertad), Brazil (Rio Grande do Sul), Chile, Paraguay (Hassel de Menéndez, 1958), and Argentina (Buenos Aires (Hässel de Menéndez, 1963), Chubut (Hässel de Menéndez, 1963), Neuquen (Hässel de Menéndez, 1963), Rio Negro (Hässel de Menéndez, 1963)), perhaps also Cuba and Trinidad (Schuster, 1992b). The species seems to be quite common and has been collected on calcareous or siliceous, sandy or clayey soil, near water edges, from sea level to 2800 m.

Distribution:Rio Grande do Sul Brazil South America| Querétaro Mexico North America| Chile South America| Cotopaxi Ecuador South America| Cajamarca Peru South America| La Libertad Peru South America|