Pleonosporium pygmaeum N.L. Gardner 1927: 379

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, Phytotaxa 340 (3), pp. 229-245 : 234-236

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.

Figures

FIGURES 17–24. Species of Pleonosporium: Pleonosporium mexicanum, 17) Apical portion of a sporophyte with incurved branchlets. Scale bar: 600 μm. 18) Sessile mature polysporangium (arrows), and an immature polysporangium (arrowhead). Scale bar: 65 μm. 19) Sessile spermatangial cluster (arrow). Scale bar: 40 μm. 20) Young procarp (arrow); note that the trichogyne has not developed. Scale bar: 50 μm. 21) Mature carposporophyte (key), note the carposporangia (arrow) and mature carposporophyte (arrowheads). Scale bar: 130 μm. Pleonosporium pygmaeum, Punta Morro, Baja California (ENCB 9570). 22) Habit of sporophyte. Scale bar: 8 mm. 23) Basal portion of thallus showing strong rhizoidal cortication (arrow). Scale bar: 160 μm. 24) Branch tip of sporophyte with straight branchlets. Scale bar: 120 μm.

FIGURES 25–32. Species of Pleonosporium: Pleonosporium pygmaeum, 25) Branch of sporophyte showing sessile polysporangia (arrow). Scale bar: 90 μm. Pleonosporium rhizoideum, Puerto Peñasco, Sonora (ENCB 16338). 26) Habit of sporophyte. Scale bar: 5 mm. 27) Basal portion of the thallus; note the attachment structure (arrow). Scale bar: 280 μm. 28) Branch tip of a sporophyte with curved branchlets. Scale bar: 100 μm. 29) Group of spermatangial clusters (arrow) borne on a single branch. Scale bar: 80 μm. 30) Group of mature carposporophytes (key), with carposporangia (arrow). Scale bar: 200 μm. Species of Spongoclonium: Spongoclonium caribaeum, Escolleras Tuxpan, Veracruz (ENCB VER-2017/A). 31) Branch tips from sporophyte showing branching axis and determinate lateral branchlets. Scale bar: 600 μm. 32) Ecorticate axis and determinate lateral branches. Scale bar: 300 μm.