Pleonosporium ricksearlesii C.W.Schneider & G.W.Saunders, 2024

Schneider, Craig W. & Saunders, Gary W., 2024, Australasian Lophothamnion J. Agardh aligns genetically with Pleonosporium Nägeli (Wrangeliaceae, Spongoclonieae): new species from the western Atlantic, Cryptogamie, Algologie 20 (1), pp. 1-10 : 4

Pleonosporium ricksearlesii C.W.Schneider & G.W.Saunders , sp. nov.

( Fig. 3 )

HOLOTYPE (DESIGNATED HERE). — Bermuda. Somerset Island , 32°16.783’N, 64°52.788’W, on wooden dock in Ely’s Harbour, depth 0-1 m, 30.VI.2015, C.W. Schneider & T.R. Popolizio 15-21-3 (holo-, MICH[1210917] ), dried silica sample: BDA1944, GenBank: OR336107 (COI-5P), OR336112 (rbc L).

ISOTYPES. — Same data as holotype (iso-, NY, UNB, Herb. CWS) .

ETYMOLOGY. — Named for Prof. Richard Brownlee Searles, the first author’s graduate mentor, collaborator and friend, on the occasion of his 87th birthday. Joint cruises with the first author to study mesophotic seaweeds off Bermuda aboard the R/V Seahawk in the early 1980s initiated four decades of investigation on the macroalgal flora of this Atlantic archipelago.

DISTRIBUTION. — Endemic to Bermuda as currently known.

DESCRIPTION

Delicate plants lignicolous or on mud-saturated wood, bushy, erect to 5.0 cm tall, Persian red in colour (Graf 1x 2023) and ecorticate ( Fig. 3A ); indeterminate axes fine with alternately irregular branching above with corymbose and narrowly-angled branches at apices, some with some branches overtopping the apex ( Fig. 3B ); most branches simple of 15 with fewer cells or once branched, indeterminate branches irregularly replacing these branches; in lower portions of indeterminate axes, the lateral branches markedly smaller than the axis that produced them ( Fig. 3C ), and with most lateral branches losing all but a few of their most proximal cells; in distal portions the axes only slightly larger in diam. than the branches they produce; indeterminate axial cells cylindrical and usually flared at their proximal ends in basal portions of main axes ( Fig. 3C, F, G ), 95-150 µm diam. and 370-530 µm long, gradually tapering distally to cells 20-30 µm diam. and 85-250 µm long several segments below the apices; upper branches incurved, apical cells slightly tapering but obtuse ( Fig. 3D ); tetrasporangia adaxially sessile on upper incurved branches, borne singly or in a series of successive cells or every other branch cell ( Fig. 3E ), subglobose to obovoidal, 33-36 µm diam. and 36-48 µm long, including a thick wall, sporangia also forming laterally or terminally, at times clustered or in secund series, on broken lower and regenerating lateral branches ( Fig. 3F, G ), some appearing to have single-celled stalks; gametangia unknown.

Figures

FIG. 3. — Pleonosporium ricksearlesii C.W.Schneider & G.W.Saunders, sp. nov., holotype specimen (CWS/TRP 15-21-3, BDA1944): A, habit of type specimen; B, apex of indeterminate axis; C, lateral branch origin from basal portion of axis; D, apex of lateral branch; E, apical portion of axis with adaxial tetrasporangia; F, terminal tetrasporangium on lateral off lower main axis with subtending branchlet or sporangial initials; G, regenerating lateral on lower axis producing a series of tetrasporangia. Scale bars: A, 2 cm; B, D, E, 100 µm; C, F, G, 50 µm.