Dictyota dichotoma (Huds.) J.V.Lamour.
J.Bot.(Desvaux) 42 (1809)

Conservation Code: Not threatened
Naturalised Status: Native to Western Australia
Name Status: Current

Distribution

Beard’s Provinces: South-West Province.

IBRA Regions: Esperance Plains, Swan Coastal Plain, Warren.

IBRA Subregions: Perth, Recherche, Warren.

IMCRA Regions: Abrolhos Islands, Leeuwin-Naturaliste, Shark Bay, WA South Coast.

Local Government Areas (LGAs): Busselton, Cockburn, East Fremantle, Esperance, Greater Geraldton, Manjimup, Rockingham, Shark Bay, South Perth.

Scientific Description
John Huisman & Cheryl Parker, Thursday 8 September 2016

Habit and structure. Thallus usually medium brown, darker near the base, 2–20 cm long, fairly regularly dichotomously branched at intervals of 0.5–1(–3) cm, branches (2–)3–7(–10) mm broad (down to 1 mm near apices of var. intricata), usually more or less linear and tapering only slightly from lower to upper parts of the thallus, rarely spirally twisted, axils more or less rounded, apices of branches rounded and usually 3–4 mm broad just below the apices (narrower in var. intricata), with occasional specimens tapering in upper 0.5–1 cm to apiculate apices; proliferations usually absent except as a response to damage, occasionally present marginally. Holdfast of rhizoids; mainly epilithic. Cortical cells 14–20 µm across, L/B 1–2(–4). Hair tufts scattered, hairs 10–18 µm in diameter.

Reproduction. Tetrasporangia 70–110 µm in diameter, usually densely scattered (singly or in small groups) over the thallus except close to the margins. Oogonia in scattered, irregularly ovate sori 150–400 µm long and 120–250 µm across; oogonia 60–90 µm long and 30–50 µm in diameter. Antheridia in scattered, ovate to irregularly elongate sori (150–)250–600 µm long and 150–250 µm across; antheridia 60–80 µm long and 20–30 µm in diameter.

Distribution. From Whitford Beach, W. Aust., around southern Australia and Tas., to southern Qld.; probably further north on both eastern and western coasts.

Habitat. In sheltered areas such as American R. inlet on Kangaroo I., Venus Bay and Port Clinton, plants are narrower than normal, with long interbranch segments, and are placed in var. intricata (C.Agardh) Grev.; to what extent this variation is ecological is not established.

[After Womersley, Mar. Benthic Fl. Southern Australia II:194–196 (1987)]