Monographs Details: Riccia lamellosa Raddi
Authority: Bischler, Hélène, et al. 2005. Marchantiidae. Fl. Neotrop. Monogr. 97: 1--262. (Published by NYBG Press)
Scientific Name:Riccia lamellosa Raddi
Synonyms:Riccia grandisquama Steph., Riccia lamellosa var. americana M.Howe, Riccia austinii Steph., Riccia indusiata S.Winkl.
Description:Species Description - Thallus forming complete or partial rosettes, or gregarious patches; lobes 20 mm long, 2-4- mm wide, rounded apically, 2-4 times forked, basal dichotomy deep, reaching 3/4 of lobe length; dorsal side pale green or bluish, with acute, pale margins; flanks inflexed, often with purplish spots. Median groove shallow and wide, persistent to lobe base. Epidermal cells convex, disintegrating, except in groove; usually 2 layers of hyaline cells beyond the epidermis. Ventral scales white, extending beyond lobe margins, semi-lunate, imbricate, of large cells (135-145 × 52-80 µm), margin entire, of smaller cells (100 × 72 µm). Cross section of lobes as wide as high near thallus apex, 1.5-2 times as wide as high below; dorsal edge laterally ascending and forming short, thin wings on both sides; flanks erect, extending into the short wings; ventral edge convex or plano-convex. Monoecious. Antheridial necks hardly protruding, pale. Sporangia large. Spores tetrahedral to nearly spherical, 76-130 µm diam., red-brown or dark brown; wing 2-4 mm wide, yellow or light brown with thickenings, margin crenulate, or incomplete, or absent; distal face with 8-15 complete areoles across diam., with thick ridges and tubercles; sometimes, areoles replaced near equator by straight ridges, or areoles only near pole, with tubercles near equator; proximal face with numerous and smaller areoles with low ridges and dark tubercles, with weak triradiate scar. Gametophytic chromosome number n = 8, 16, 24.

Discussion:Riccia lamellosa is easily recognized by its pale-green or bluish color and by its white scales covering the flanks and extending beyond the lobe margins. Variation is observed in the degree of imbrication of the scales, scale color (usually white but sometimes with pink, violaceous or brown spots), spore diam. (80-84 to 98-120 µm), the spore wing, which may be wide (3-6 µm) or incomplete to absent, and the number of areoles across distal spore faces (8-9 to 10-15). The morphological variation observed is not geographical and but may correlate with ecology because the species occurs in a large variety of habitat conditions, and also with polyploidy (n = 8, 16 or 24). The genetic structure of R. lamellosa requires investigation.

Distribution and Ecology: Riccia lamellosa is widely distributed in C Europe and the Mediterranean area, Macaronesia (Canary Is., Madeira), dry tropical and subtropical Africa (Ethiopia, C Africa, Tanzania, Kenya, S Africa), C and SW Asia (Syria, Kazakhstan, Tajikistan, Pakistan), and Australia. It is known from Canada, and from the U.S.A. from most states. In the Neotropics, it has been recorded from Mexico (Baja California (Schuster, 1992b), D. F., Mexico, Puebla, Querétaro, Zacatecas), Colombia (Winkler, 1976, as R. indusiata; Gradstein, 1998), Peru (Pasco (Bryan, 1929)), Brazil (Rio Grande do Sul), Argentina (Catamarca (Muller, 1955), Tucumán (Hässel de Menéndez, 1958), La Rioja (Hässel de Menéndez, 1958), Buenos Aires (Hässel de Menéndez, 1958)), and Uruguay. The species is rare in the Neotropics; it has been collected in semi-arid zones on calcareous or siliceous, sandy soil or clay, among rocks and lava, exposed in grasslands or along paths, or sheltered in open, scrubby vegetation or woodland, from sea level to 4200 m.

Distribution:Rio Grande do Sul Brazil South America| Zacatecas Mexico North America| Querétaro Mexico North America| Distrito Federal Mexico North America| México Mexico North America| Puebla Mexico North America| Durazno Uruguay South America| Tacuarembó Uruguay South America| César Colombia South America|