Digenea simplex (Wulfen) C.Agardh

Scientific Description

Habit and structure. Thallus erect, arising from a discoid holdfast, to 15 cm tall, dark purple to almost black, the surface generally with a covering of epiphytes and accumulated debris, dichotomously to irregularly branched every 10–30 mm. Axes terete, villose (sometimes denuded below), 3–5 mm diam., with a medulla of large hyaline cells 140–200 μm diam., grading to a thin pigmented cortex of 1 or 2 cell layers. Determinate branches terete, 100–130 μm diam., tapering only slightly distally, then abruptly at the apices. Pericentral cells in determinate branches each cutting off 2 or 3 periclinal cortical cells, each then dividing obliquely or transversely several times. Trichoblasts sparsely to well-developed at the apices of determinate branches, rapidly shed, to 200–400 μm long, with an essentially percurrent axis of comparatively large cells, to 15–17 μm diam. [L:B c. 2], bearing markedly thinner secund lateral branches, tapering to 2–3 μm diam. Scar cells occasionally present.

Reproduction. Reproductive structures not observed.

Distribution. Widely distributed in tropical seas.

Habitat. Epilithic in the intertidal and shallow subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 503–504 (2018)]