Pleonosporium pygmaeum N. L. Gardner 1927
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 pygmaeum

description: Pleonosporium pygmaeum N.L. Gardner 1927: 379, pl. 79: fig. 2, pl. 80 (Figs. 22–25)   
 Type locality: cast ashore; on seagrass, Phyllospadix; La Jolla, San Diego County, California, USA.   
 Distribution. EASTERN PACIFIC. California, USA; Baja California, México; and El Salvador (Dawson 1961, Guiry and Guiry 2017; herein).   
 Specimens studied. PACIFIC MÉXICO: Baja California: Punta Morro (116°39’45”W, 31°51’41”N), coll. Mendoza-González & Mateo-Cid, 31-07-1987 (ENCB 9570; polysporangia); and, Raul´s, north of Ensenada (116°39’34” W, 31°51’36” N), coll. R. Aguilar Rosas, 12-04-2000 (CMMEX 3698; polysporangia).   
 Habitat. Epiphytic on Osmundea spectabilis (Postels & Ruprecht) K.W. Nam; intertidal, in tide pools.   
 Morphology, Anatomy and Reproductive structures. Thalli flaccid, soft pink, 1.5–2.5 cm high, with percurrent axes, branching more or less alternate-distichously; upper main branches often longer than the lower ones; lower portions of thallus lightly corticated by slender, descending rhizoidal filaments; attached by numerous rhizoids. Primary axes 300–350 μm in diameter and 300–500 μm long; primary axes and branches of first and second orders corticated by slender, branched, descending rhizoidal filaments from the basal cell of lateral branches; ultimate indeterminate branchlets 30–40 μm in diameter at the base, upward becoming tapered and adaxially curved, with blunt apices.   
Polysporangia spherical, 60–70 μm in diameter (including thick hyaline cell wall), divided into 32 spores; borne adaxial on simple third-order branchlets. Gametangial plants not observed.  
 Remarks. Uncertain if Pleonosporium pygmaeum should be recognized as a distinct species, Dawson (1962a:42) observed material from Cortes Bank, California Channel Islands (EYD-8010) in agreement with P. pygmaeum N.L. Gardner (1927). He noted the species could be characterized by its small size, 0.6–2.0 cm, and the corticating filaments restricted to its lowermost base. Although Dawson (1962a) also suggested it could be a dwarfish, little corticated, variant of P. dasyoides (J. Agardh) De Toni, he did not treat it as a synonym. Later, Abbott (1972) considered both P. pygmaeum and P. dasyoides as being conspecific with P. squarrulosum (Harvey) I.A. Abbott.   
 Our Mexican specimens are much smaller than of P. dasyoides as reported from Pacific Baja California, i.e., 5–10 cm tall (Dawson, 1962a) and 5–20 cm tall from California (Abbott and Hollenberg,1976). We tentatively refer our Mexican specimen to P. pygmaeum, pending phylogenetic analyses to test its taxonomic status and verify its presence in Pacific Mexico.
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 pages 234-236, DOI: 10.11646/phytotaxa.340.3.3, http://zenodo.org/record/13720321