Polysiphonia sertularioides (Gratel.) J.Agardh

Scientific Description

Habit and structure. Thallus dark red-brown, 2–8(–14) cm high, usually in dense, soft and somewhat gelatinous tufts or masses, with a tangle of prostrate filaments producing very numerous erect, slender, fastigiate, much-divided branches. Attachment from prostrate filaments; epilithic, occasionally epiphytic. Structure. Prostrate filaments 100–130(–250) µm in diameter with segments L/D 1–2, attached by scattered unicellular rhizoids with digitate haptera, cut off from the proximal end of pericentral cells. Erect branches 70–150(–200) µm in diameter with segments L/D (0.8–)1–3(–4), occasionally extending to L/D up to 12 in mid and lower parts of long branches, decreasing gradually to 25–50 µm in diameter and segments L/D 0.5–1.5 shortly below the apices; apices straight, with fairly prominent apical cells and usually profuse trichoblasts; lateral branches arising close to apices from the basal cell of a trichoblast which remains simple or once furcate; cicatrigenous branches occasionally arise from lower parts. Pericentral cells 4, elongate throughout the thallus, ecorticate throughout; trichoblasts (or scar cells) formed on every segment with a divergence of one quarter, relatively slender, (1–)2–3(–4) times furcate. Rhodoplasts discoid, scattered or in chains.

Reproduction. Gametophytes dioecious. Carposporophytes with a slight basal fusion cell and short gonimoblast with pyriform to clavate terminal carposporangia 25–40 µm in diameter. Cystocarps stalked, subspherical to slightly urceolate, 150–300 µm in diameter; pericarp ostiolate, 2 cells thick, outer cells elongate, L/D 1.5–2 when mature. Spermatangial branches developing as one branch of a trichoblast, cylindrical and tapering slightly, 120–250 µm long and 30–60 µm in diameter, without a sterile apical cell when mature. Tetrasporangia forming regular, slightly spiral to almost straight, prominent series in upper branches, occasionally in isolated rows of 3–6, when in laterals with the lower few segments sterile and narrower, often extending below a branch, slightly to considerably but evenly swelling the branch with the mature sporangia occupying most of the branch width, subspherical to ovoid, 35–65 µm in diameter, tetrahedrally (often subcruciately) divided.

Distribution.Mediterranean, New Zealand. In Australia, the Dampier Archipelago and from Rottnest I., and North Beach (Perth), W. Aust., along the southern coast to Western Port, Vic., (probably to Queensland) and around Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 184–186 (2003)]