Pleonosporium mexicanum E. Y. Dawson 1962
Creators: name: Mateo-Cid, Luz Elena
name: Mendoza-González, A. Catalina
name: Norris, James N.
name: García-López, Deisy Y.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Plantae
Rhodophyta
Florideophyceae
Ceramiales
Wrangeliaceae
Pleonosporium
Pleonosporium mexicanum

description: Pleonosporium mexicanum E.Y. Dawson 1962a: 41 (Figs. 15–21)   
 Type locality: Lowermost intertidal on small reef 3 km. north of Belmar Hotel, Playa de Olas Altas, Mazatlán, Sinaloa, Gulf of California, México.   
 Distribution. EASTERN PACIFIC. Gulf of California, México: Sonora, Baja California Sur, Sinaloa, and Nayarit. Pacific México: Baja California (Isla Guadalupe), Baja California Sur, Jalisco, Michoacán, Guerrero, and Oaxaca; El Salvador; and Costa Rica (Mendoza-González et al., 1994; Mateo-Cid et al., 2006; Bucher and Norris, 2014; Norris et al. 2017; herein). WESTERN ATLANTIC: Brazil (Oliveira Filho, 1977).   
 Specimens studied. GULF OF CALIFORNIA: Nayarit: Lo de Marcos (105°21’20” W, 20°57’17” N), coll. Huerta Múzquiz, Casas Valdés & Hernández, 25-05-1973 (ENCB 3016; polysporangia). PACIFIC MÉXICO: Jalisco: Playa Conchas Chinas (105°14’02”W, 20°36’45”N), coll. Mendoza-González & Mateo-Cid, 08-10-1997 (ENCB 16739; ♀, ♂); Michoacán: Playa La Salada (102°62’63” W, 18°05’16” N), coll. Mendoza-González & Mateo-Cid, 16-12-2006 (ENCB MICH-A/1; ♀, ♂, polysporangia); Guerrero: Las Peñitas (102°03’88”W, 17°98’91”N), coll. Mateo-Cid & Mendoza-González, 17-12-2009 (ENCB 19551; ♀, polysporangia); Playa Manzanillo-La Majahua (101°44’55”W, 17°48’08”N), coll. Mendoza-González & Mateo-Cid, 24-09-2007 (ENCB 19535; polysporangia); Playa Las Gatas, Zihuatanejo (101°33’05”W, 17°37’12”N), coll. Mateo-Cid & Mendoza-González, 08-11-1996 (ENCB 19434; polysporangia); and, Oaxaca: Morro de Cerro Hermoso (97°33’30”W, 15°57’34”N), coll. Mendoza-González & Mateo-Cid, 23-02-1996 (ENCB 14961; polysporangia), Santa Elena Cozoaltepec (96°44’38”W, 15°43’14”N), coll. Mateo-Cid & Mendoza-González, 22-02-1996 (ENCB 14964; ♂, ♀, polysporangia), Playa Agua Blanca (96°48’50”W, 15°43’58”N), coll. Mendoza-González & Mateo-Cid, 08-08-1992 (ENCB 14962; polysporangia), Puerto Ángel (96°29’42”W, 15°39’46”N), coll. Mendoza-González & Mateo-Cid, 26-02-1996 (ENCB 14960; polysporangia), and Tangolunda (96°05’58”W, 15°46’10”N), coll. Mendoza-González & Mateo-Cid, 08-08-1993 (ENCB 14959; polysporangia).   
 Habitat. On rocks, and epiphytic on Amphiroa beauvoisii J.V. Lamouroux; intertidal to subtidal.   
 Morphology Anatomy and Reproductive structures. Thalli erect, bushy, tufts 2-5 cm tall, reddish green; primary axes ecorticate, commonly barren of branches in lower and mid-portions; upwards alternate, distichously branched (but not from every cell); branches bearing distichous, alternate, determinate lateral, mostly unbranched, branchlets from each cell, somewhat incurved; attached by a group of long, little-divided, multicellular, rhizoids. Axial cells of main filaments (110–) 150–190 (–225) μm in diameter and 240–300 μm long; middle cells 70–80 μm in diameter and (100–)120–160 μm long; determinate lateral branchlets usually simple, of 15–30 cells, 40–60 μm in diameter basally, becoming strongly incurved upwards, somewhat corymbose, outwards cells 25–40 in diameter and 40–60 μm long, ultimate cell, about 25 μm in diameter with blunt apices.   
Polysporangia sessile, broadly ovoid, about (70–) 80–100 μm in diameter (including thick hyaline cell wall); divided into thirty-two spores; borne in mainly adaxial series along lateral branches. Gametangial thalli dioecious. Spermatangial clusters about 75–80 μm long, 30–35 μm in diameter; sessile, adaxial on lateral branchlets. Cystocarps subspherical, about 250–280 μm in diameter; borne on the terminal portions of thallus.  
 Remarks. Although mostly in agreement with P. mexicanum E.Y. Dawson (1962a), our specimens were taller and the main axes had larger cells than those he described. It is now reported for the first time for the coast of Michoacán in Pacific México.
description: Published as part of Mateo-Cid, Luz Elena, Mendoza-González, A. Catalina, Norris, James N. & García-López, Deisy Y., 2018, A taxonomic account of species in the tribe Spongoclonieae (Ceramiaceae, Ceramiales, Rhodophyta) reported from Atlantic and Pacific Mexico, pp. 229-245 in Phytotaxa 340 (3) on page 234, DOI: 10.11646/phytotaxa.340.3.3, http://zenodo.org/record/13720321