Padina mexicana

Padina mexicana E. Y. Dawson var. mexicana

Padina mexicana E. Y. Dawson, 1944:231, pl. 52: fig. 2; Dawson, 1959a:19; Dawson, 1961b:389; Dawson, 1966a:11; Chávez B., 1980:48; Huerta-Múzquiz and Mendoza-González, 1985:46; Mateo-Cid and Mendoza-González, 1991:24; Rocha-Ramírez and Siqueiros-Beltrones, 1991:31; Mateo-Cid et al., 1993:50; Servière-Zaragoza et al., 1993:482; Mendoza-González et al., 1994:110; Mateo-Cid and Mendoza-González, 1994b:43; González-González et al., 1996:156; Pacheco-Ruíz and Zertuche-González, 1996b:171; Anaya-Reyna and Riosmena-Rodríguez, 1996:862; Riosmena-Rodríguez et al., 1998:45; Ávila-Ortiz and Pedroche, 1999:357; L. Aguilar-Rosas et al., 2000:132; Mateo-Cid et al., 2000a:68; Mateo-Cid et al., 2000b:211, figs. 54–56, 83–86, 106; Cruz-Ayala et al., 2001:190; Ávila-Ortiz, 2003:70, figs. 1–9: López et al., 2004:10; Ávila-Ortiz and Pedroche, 2005:158, figs. 37 (isotype), 38–41; Riosmena-Rodríguez et al., 2005:102; Mateo-Cid et al., 2006:49; Pacheco-Ruíz et al., 2008:203; Pedroche et al., 2008:54.

Algae low-growing, more or less prostrate, fan-shaped blades, light chalky whitish to grey-brown; blades often overlapping, forming clustered rosettes, attached to each other and to substratum by multicellular rhizoids along the lower portions of blades (without a stipe). Blades mostly entire, 1.5–3(–5) cm tall and 1.5–5.0 cm wide; moderately calcified (mostly on lower surface); concentric bands of hairs alternate with calcification. Blades near inrolled margin of 2 cell layers, 35–80(–100) µm thick; midportion of 4 cell layers, 90–170 µm thick; lower portions of 5–6 cell layers, 150–200(–280) µm thick. Cortical cells 17–33 µm

tall by 22–36 µm wide; medullary cells 19–37 µm by 24–48(–56) µm wide.

Sporangia in sori covered with a thin indusium; 90–120 µm long by 50–90 µm in diameter; patchy or discontinuous in irregular lines between the concentric bands of calcium carbonate only on the upper side. Oogonia 92–96 µm tall (Mateo-Cid et al., 2000b) by 73 µm in diameter; in sori with indusium (when immature), in concentric lines (Ávila-Ortiz and Pedroche, 2005). Antheridia not known.

HABITAT. On sand-covered rocks and tidal platforms; mid intertidal to shallow subtidal, to 3.3 m depth.

DISTRIBUTION. Gulf of California: Puerto Peñasco to Cabo Pulmo. Pacific coast: Todos Santos, Baja California Sur; Sinaloa to Oaxaca.

TYPE LOCALITY. Isla Turners, off southeast Isla Tiburón, Las Islas de la Cintura, Gulf of California.