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Dictyomenia sonderi Harv.

Reference
Phycol.Austral. Pl. XXI (1858)
Conservation Code
Not threatened
Naturalised Status
Native to Western Australia
Name Status
Current
Image

Scientific Description

Habit and structure. Thallus medium to dark red-brown, erect, 10–40 cm high, complanately and marginally branched with regularly to irregularly pinnate lateral branches, linear and (3–)4–6(–7) mm broad, with regular marginal fringes of branched determinate laterals 1–2(–3) mm long. Main branches with a well defined midrib and prominent alternate lateral veins, midrib thickened below and remaining as a subterete stalk 1–1.5(–2) mm thick where the lateral membrane is lost. Branch blades corticated from close to apices. Holdfast fibrous, branched, 1–2 cm across; epilithic. Structure. Apical cell of branches dome-shaped, 7–15 µm in diameter, with the axial cells branching on alternate sides every 2 cells to originate determinate laterals and cutting off 6 pericentral cells, 2 larger lateral ones and 2 smaller ones on each side. The determinate laterals remain active for some time, cutting off the 6 pericentral cells and the lateral pericentral cells forming chains of 2–3, resulting in (3–)5–6 large inner cells between the lateral veins; the determinate laterals fuse congenitally to form the 4–6 mm broad main branches, with the apices of the determinate laterals forming the marginal fringe; trichoblasts occur as dense tufts on the end branches of the determinate laterals. Cortication generally 1(–2) cells thick over the blades, heavier over the midrib. Cells probably uninucleate; rhodoplasts discoid.

Reproduction. Reproductive organs borne on branched clusters arising over the lateral veins on the branch surface. Gametophytes dioecious. Procarps not observed. Carposporophytes with a basal fusion cell and branched gonimoblast with clavate terminal carposporangia 35–90 µm in diameter. Cystocarps subspherical to slightly ovoid, 700–1500 µm in diameter; pericarp ostiolate, corticated. Spermatangial organs with 1–2 sterile basal cells, no sterile apical cells, ovoid to slightly tapering, 60–90 µm in diameter and 100–150 µm long. Stichidia in much-branched clusters 1–2 mm high, branches 100–180 µm in diameter with segments L/D 0.4–0.8, tetrasporangia single per segment, in short series maturing acropetally, 130–200 µm in diameter.

Distribution.N of Dongara, W. Aust., to Backstairs Passage, S. Aust; doubtfully N Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 347–349 (2003)]

John Huisman & Cheryl Parker, 3 August 2021

Distribution

IBRA Regions
Esperance Plains, Geraldton Sandplains, Swan Coastal Plain, Warren.
IBRA Subregions
Geraldton Hills, Perth, Recherche, Warren.
IMCRA Regions
Abrolhos Islands, Central West Coast, Leeuwin-Naturaliste, Pilbara (nearshore), Pilbara (offshore), WA South Coast.
Local Government Areas (LGAs)
Ashburton, Augusta Margaret River, Busselton, Cockburn, Dandaragan, Esperance, Greater Geraldton, Irwin, Joondalup, Karratha, Mandurah, Northampton, Rockingham, Wanneroo.