Pleonosporium vancouverianum (J. Agardh) J. Agardh, 1892: 37

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 : 238-239

Pleonosporium vancouverianum (J. Agardh) J. Agardh, 1892: 37 .

For illustrations see: Kylin, 1925: 57, figs. 37A–C; Dawson, 1962a: 39, pl. 13: fig. 3; Abbott and Hollenberg, 1976: 618, fig. 562; Bucher and Norris, 2014: 302, figs. 149A-C.

Basionym : Callithamnion vancouverianum J. Agardh, 1876: 30 .

Synonyms: Pleonosporium abysicola N.L. Gardner, 1927: 380 ; Pleonosporium vancouverianum Setchell & N.L. Gardner, 1903: 338 .

Type locality: “ad insulam Vancouveri” ( J. Agardh, 1876: 30; 1892: 37); Vancouver Island, British Columbia, Canada.

Distribution. EASTERN PACIFIC. PACIFIC MÉXICO: Islas Todos Santos (Bahía de Todos Santos; vicinity of Ensenada), Isla Guadeloupe, and Arrecife Sacramento, Baja California; and Isla Magdalena, Baja California Sur. GULF OF CALIFORNIA: Isla Coronado and Islas de Los Gemelos (both Bahía de Los Ángeles), Baja California; and Bahía Chacala, Nayarit ( Aguilar-Rosas et al., 1990; Mateo-Cid and Mendoza-González, 1992; Bucher and Norris, 2014).

Habitat. Epiphytic or entangled on other algae; shallow subtidal, down to 20 m depths.

Morphology, Anatomy and Reproductive structures. Thalli of few to several erect, ecorticated, axes of uniseriate filaments, up to 1.0 (–1.8) cm tall; branching from almost every cell, distichous and alternate, up to 4 (–5) orders; each order progressively smaller than proceeding one; attached by a few, wide filament-like rhizoids at base of axes, and by long, thin (to 20 μm in diameter), unbranched, multicellular rhizoids issued singly, from the middle of some lower axial cells. Cells of main axes and primary branches, cylindrical, basally 150–240 μm in diameter and to 340–680 μm long, becoming smaller above and cuboid. Proximal cell of lateral branches slightly shorter than adjoining cells. Ultimate branchlets of 2–6 cell long; cells about 1-2 diameters long; terminal cells with rounded tips, about 10 μm in diameter.

Mature polysporangia ovate to oblong-ellipsoidal, to 75 μm in length and to 45 μm wide, divided into about 16 spores; sessile, borne alternately in position of ultimate branchlets. Sexual plants not found in Gulf of California or Pacific Mexico material.

Remarks. Pleonosporium vancouverianum is somewhat similar to P. squarrosum squarrulosum Kylin (1925: 57 , figs. 37D-G), but differs primarily in having rounded to blunt branch apices, ellipsoidal polysporangia, and spermatangia alternate on both upper and lower sides of ultimate branchlets, versus the attenuated branch apices, oviform polysporangia, and spermatangia restricted to upper sides of ultimate branchlets in P. squarrosum ( Gabrielson et al., 2000) .

Although Pleonosporium abysicola N.L. Gardner (1927) was accepted as a synonym of P. vancouverianum by some ( Hollenberg and Abbott, 1966; Abbott and Hollenberg, 1976; Guiry and Guiry, 2016), others recognize it as a distinct species (e.g., Scagel et al., 1989; Gabrielson et al., 2000; Enciso-Padilla and Serviere-Zaragoza, 2006). Both species lack significant cortication and have sessile polysporangia, but differ in orders of branching; P. abysicola has 5 (rarely 6) orders of branching, and P. vancouverianum 3–4 orders ( Gabrielson et al., 2000: 47).

Dawson (1962a) measured cells in the type figure of P. abysicola N.L. Gardner (1927 : pl. 81: fig. 1; TL: dredged, near Friday Harbor, San Juan Island, Washington) to be 2.5 3.0 diameters long, and noted Gardner’s text description (1927: 380) mistakenly stated cell sizes of main axes as “3.0 4.0 diameters long” and primary branch as “4.0 6.0 diameters long.” Northern Gulf of California specimens referred to P. vancouverianum by Bucher and Norris (2014) had axial cells 150 240 μm in diameter and 340 680 μm in length (about 2.3 2.83 diameters long), measurements similar to the type of P. abysicola ( Gardner, 1927) and those reported from Pacific Baja California ( Dawson, 1962a). For now, we treat the Pacific Baja California and the northern Gulf of California specimens as P. vancouverianum . Further comparative morphological and molecular phylogenetic studies are needed to clarify the identity of the Mexico specimens referred to P. abysicola ( Dawson, 1962a; Mateo-Cid and Mendoza-González, 1992) and P. vancouverianum ( Bucher and Norris, 2014) with comparisons to the type materials of these species.