Monographs Details: Riccia nigrella DC.
Authority: Bischler, Hélène, et al. 2005. Marchantiidae. Fl. Neotrop. Monogr. 97: 1--262. (Published by NYBG Press)
Scientific Name:Riccia nigrella DC.
Synonyms:Riccia aggregata Underw.
Description:Species Description - Thalli forming rosettes, or gregarious, crowded mats; lobes 1-1.2 mm wide, acute or obtuse apically, 3 times forked with lobes divaricate at 40°, the basal dichotomy deep (2.5 mm), the following at 1.5 mm and the last short (0.2-0.6 mm); dorsal side dark blue-green, red-brown basally, on ventral side and on the narrow margins, margins inflexed when dry and lobes showing only the black flanks, appearing as black threads. Median groove deep, narrow. Epidermal cells persistent, hyaline, convex, 1.5 times higher than hypodermal cells. Ventral scales large, imbricate, semi-lunate, reaching or extending beyond lobe margins, dark violet or nearly black and glossy, with entire, pink margins. Cross section of lobes 0.8 mm high, 1-1.5 times as wide as high; dorsal edge acute laterally; flanks ascending, recurved apically and acute; ventral edge convex; dorsal tissue reaching half of lobe height. Monoecious. Archegonial necks long, black. Sporangia hardly bulging, dorsal tissue above the sporangia usually red-brown. Spores 60-80 µm diam., light brown; wing 5-7 µm wide, faintly crenulate with a few dark, vermiculate ridges; distal face with 8-9(-10) areoles across diam., incompletely delimited by irregular, thick, sinuose and anastomosed, dark brown ridges, some areoles with partly thin or vanishing ridges, more complete and smaller areoles with tubercles on the ridges near equator; proximal face with complete areoles and large tubercles, or not areolate, with irregular, thick and sinuose, bifurcate ridges, triradiate scar thin, sometimes interrupted. Gametophytic chromosome number n = 8.

Discussion:Riccia nigrella is easily recognized by its black and glossy lateral flanks, and its narrow, bluish green lobes tinged with red-brown basally and on the margins.

Distribution and Ecology: Riccia nigrella is widely distributed in C and Atlantic Europe, reaching northward to Great Britain, in the Mediterranean area, Macaronesia, S Africa, China, and Australia. It is nown from S United States (Arizona, California, Georgia, Texas), and has been recorded in the Neotropics from Mexico (Baja California (Howe, 1934), D. F., Guadalupe Is. (Howe, 1934), Oaxaca). The species is infrequent in the Neotropics. It has been collected on soil with lava fragments or in seepage areas, from sea level to 2300 m.

Distribution:Distrito Federal Mexico North America| Oaxaca Mexico North America|