Pentocladia australiensis Huisman

Scientific Description

Habit and structure. Thallus dark red, with prostrate indeterminate axes spreading to 5 mm. Attachment rhizoids arising singly in a medial position on ventral pericentral cells of indeterminate axes, reaching 35–120 µm in length before cutting off 6–9 radial subapical cells and 1 apical cell, these elongating and dividing dichotomously 1 or 2 times. Indeterminate axes 100–135 µm diam. [segment L:B 1–1.2], each segment with 5 pericentral cells and a branch primordium, determinate branch, or indeterminate branch as described for the genus. Determinate branches curved, 250–500 µm long, 60–85 µm diam., with 10 or 11 segments [L:B 0.6–1]. Apices of determinate branches with 3 or 4 sequentially developing pseudodichotomously branched trichoblasts, to 600 µm long at maturity; basal cell 30–35 µm diam. [L:B 1–2]; distal cells progressively narrower and elongate.

Reproduction. Spermatangia borne in whorls on unbranched trichoblasts, these replacing vegetative trichoblasts, the basal and 3 apical cells remaining naked. Fertile spermatangial region 120–170 µm long, 35–70 µm wide. Spermatangia ellipsoidal, 3–4 µm long. Cystocarps terminating determinate branches, urn shaped, 340–400 µm diam., with clavate carposporangia 50–90 µm long and 15–25 µm diam. Other reproductive structures not observed.

Distribution. Only known from the type collection, Flacourt Bay, Barrow Island, Western Australia.

Habitat. epiphytic on Halimeda sp. in the shallow subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 558 (2018)]