Pleonosporium borreri (Smith) Nägeli 1862: 342

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 : 230-232

Pleonosporium borreri (Smith) Nägeli 1862: 342 ( Figs. 5–8 )

Basionym : Conferva borreri Smith, 1807 : pl. 1741.

Homotypic synonym: Callithamnion borreri (Smith) C. Agardh, 1828: 170 .

Type locality: Yarmouth, Norfolk, England, UK ( Maggs and Hommersand, 1993: 168; Silva et al., 1996: 419).

Distribution. WESTERN ATLANTIC: Massachusetts to Delaware, USA ( Mathieson and Dawes, 2017); Veracruz, México; and Brazil ( Taylor, 1957; Guiry and Guiry, 2017; herein). WESTERN PACIFIC: Japan; South China Sea; and Vietnam ( Titlyanov et al., 2006; Nguyen et al., 2013; Phang et al., 2016).

Specimens studied. WESTERN ATLANTIC: Veracruz ( Gulf of Mexico), México: Playa El Pulpo, Barra de Cazones (97°11´90.72´´W, 20°43´33.98’’N), coll. Mendoza-González & Mateo-Cid, 19-01-2017 ( ENCB 22896 ; polysporangia) .

Habitat. On rocks; shallow subtidal, 1–2 m deep.

Morphology, Anatomy and Reproductive structures. Thalli erect, dense filamentous tufts, up to 2.5 cm tall, rosy, with percurrent axes, branching alternately-distichous; branchlets incurved, with obtuse apices; lower portions lightly corticated by uniseriate filaments; attached by entangled, multicellular rhizoids. Cells cylindrical in proximal portions of main axes, 150–200 μm in diameter, 125–200 μm long; lateral axes gradually tapering, with middle cells 85–100 μm in diameter, 120–240 μm long; and cells of ultimate segments, 20–25 μm diameter, 60–75 μm long.

Polysporangia sessile, single, subglobose, 60–75 μm in greatest dimension (including thick hyaline cell wall), divided into sixteen spores; borne distally and adaxially on branch cells. Gametangial thalli not observed.

Remarks. Pleonosporium borreri (generitype) was originally described from temperate waters of Yarmouth, Norfolk, England ( Smith, 1807). Since then P. borreri has been reported from a wide ranging regions and habitats: subboreal to subtropical eastern Atlantic, temperate to tropical western Atlantic, temperate to subtropical western Pacific, and from subtropical to tropical Indian Ocean (e.g., Silva et al., 1996; Guiry and Guiry, 2017). Schneider and Searles (1991: 391) noting P. borreri was from cooler northerly waters removed it from the marine flora of the Carolinas, western Atlantic.

In general, the features observed in our specimens are similar to those described from northern Spain ( Secilla, 2012) and the British Isles ( Maggs and Hommersand, 1993), which had spherical to ovoid, polysporangia that were larger, 72–104 μm wide, 80–106 μm long; whereas in our Mexican specimens the polysporangia were subglobose and smaller, 60–75 μm. Further morphological and phylogenetic analyses will enable verification of its identification. Our report of P. borreri in the southwestern Gulf of Mexico represents the first report of its occurrence in Atlantic México.

Figures

FIGURES 1–8. Species of Pleonosporium. 1–4: Pleonosporium boergesenii, Playa El Pulpo, Barra de Cazones, Veracruz (ENCB 21801). 1) An entire, mature sporophyte. Scale bar: 7 mm. 2) Ecorticate branching axis and determinate lateral branch. Scale bar: 250 μm. 3) Branch tip of sporophyte showing incurving branchlets. Scale bar: 20 μm. 4) Branch of sporophyte showing sessile polysporangia (arrow). Scale bar: 60 μm. 5–8: Pleonosporium borreri, Playa El Pulpo, Barra de Cazones, Veracruz (ENCB 21896). 5) Habit of mature sporophyte. Scale bar: 8 mm. 6) Basal portion of thallus showing rhizoidal attachment. Scale bar: 150 μm. 7) Branch tip of sporophyte showing incurving and curved branchlets. Scale bar: 125 μm. 8) Branch of sporophyte with sessile polysporangia (arrows). Scale bar: 50 μm.