Pleonosporium squarrulosum (Harvey) I.A. Abbott, 1972: 262

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

Pleonosporium squarrulosum (Harvey) I.A. Abbott, 1972: 262

For illustrations see: Dawson, 1962a, as P. dasyoides : 40, pl. 13: figs.1–2; Abbott and Hollenberg, 1976: 618, fig. 561.

Basionym : Callithamnion squarrulosum Harvey, 1853: 232 .

Heterotypic synonyms: Pleonosporium dasyoides (J. Agardh) De Toni, 1903: 1310 ; Callithamnion dasyoides β californicum J. Agardh, 1876: 31 .

Type locality: “Golden Gate, California ” ( Harvey, 1853: 233); [entrance to San Francisco Bay], San Francisco, California, USA ( Abbott, 1972; Abbott and Hollenberg, 1976).

Distribution. EASTERN PACIFIC.PACIFIC MÉXICO: Punta Descanso to Bahía Blanco, northern Baja California ( Dawson, 1962a, as P. dasyoides ). GULF OF CALIFORNIA: Bahía de Loreto, Baja California Sur ( CONANP, 2002; Bucher and Norris, 2014; Norris et al., 2017).

Habitat. Epiphytic on other algae, and epizooic on hydroids and possibly other invertebrates; intertidal to subtidal; dredged from 18–30 m depths.

Morphology, Anatomy and Reproductive structures. Thalli 5–10 cm tall, usually epiphytic; axes mostly about 300 μm in diameter (can be up to 1000 μm in diameter near base); alternately more or less distichously branched; lower thallus lightly to heavily corticated by slender descending rhizoidal filaments from basal cell of lateral branches; apices of branches attenuate; upper branches of main axis often longer than lower branches; ultimate branchlets, 11–16 cells in length, slightly tapered, more or less adaxially curved, cells about as long as broad; with basal cells about 40 μm in diameter.

Polysporangia oviform, 65–75 μm long; terminal on simple or compound branchlets of one to several cells, arising near base of determinate lateral branches. Spermatangia on upper sides of ultimate branchlets; a terminal, subcylindrical or subconical cluster above a base of 1–3 sterile cells.

Remarks. Pleonosporium squarrulosum is distinguished from other Mexican species of the genus by its lower thallus cortication, the large diameter of basal cells, and short terminal branches. Although reported in Pacific Mexico ( Dawson, 1962a) and the southern Gulf of California from Bahia de Loreto ( CONANP, 2002; Bucher and Norris, 2014) to La Paz, Baja California Sur ( Norris et al., 2017), the finding of reproductive thalli for morphological and genetic comparisons are needed to verify its presence in Mexico.