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Electronic Flora of South Australia Species Fact Sheet

Microdictyon umbilicatum (Velley) Zanardini.

Phylum Chlorophyta – Order Cladophorales – Family Anadyomenaceae

Selected citations: Setchell 1929: 503, figs 21–27. Womersley 1956: 362.

Thallus (Fig. 72A) medium to dark grey-green, 10–30 (–45) cm across, firm but delicate, irregularly lobed and lacerate, with an obscure umbilicate base, probably usually epiphytic. Blade essentially monostromatic but with occasional tertiary branches displaced to one side of an earlier branch; branching of filaments alternate, opposite, or with up to six secondary filaments radiating from one point (Fig. 72B ). Primary filaments 180–220 µm in diameter, cells L/B 1.5–3; secondary filaments 80–140 µm in diameter, L/B 2–4, with a rounded tip when free; attachment of filaments by smooth adherence of un-modified ultimate segments (Fig. 72C); meshes of net irregular; division of segments by ingrowth from the peripheral wall; chloroplast reticulate, composed of numerous, round, pyrenoid-bearing areas with narrow connections.

Reproduction: Reproduction unknown.

Type from New South Wales (Port Jackson?); holotype in LIV.

Selected specimens: Cape Vlaming, Rottnest I., W. Aust., lower eulittoral (Smith, Nov. 1951; ADU, A50594 and UWA 310). Cape Riche, W. Aust. (Harvey, Alg. Aust. Exsicc. 568C, in NSW). Coobowie, S. Aust., uppermost sublittoral (Brock, 17.x.1980; ADU, A51823 and Womersley, 12.ii.1981; ADU, A51994-"Marine Algae of southern Australia" No. 225). E. side of Ballast Head, Kangaroo I., S. Aust., drift (Womersley, 28.xii.1948; ADU, A10461). Balmoral, Port Jackson, N.S.W. (Lucas, Dec. 1932; ADU, A62). Nerang R., Southport, Qld (Cribb 53.1, 11.v.1950; ADU, A14460).

Distribution map based
on current data relating to
specimens held in the
State Herbarium of SA

Distribution: Rottnest I. and Cape Riche, W. Aust and from Coobowie, Yorke Pen. to Victor Harbor, and American River Inlet, Kangaroo I., S. Aust., Port Jackson, N.S.W. and Southport, Qld. Usually in calm bays and inlets. New Zealand? (Chapman 1956, p. 441).

Taxonomic notes: M. umbilicatum is a distinctive species growing under moderate water movement only. Superficially it can apppear like an Ulva until its reticulate thallus is observed.


CHAPMAN, V.J. (1956). The marine algae of New Zealand. Part I. Myxophyceae and Chlorophyceae. J. Linn. Soc. Bot. 55 (360), 333–501, Plates 24–50.

SETCHELL, W.A. (1929). The genus Microdictyon. Univ. Calif Publ. Bot. 14, 453–588.

WOMERSLEY, H.B.S. (1956). A critical survey of the marine algae of southern Australia. I. Chlorophyta. Aust. J. mar. freshw. Res. 7, 343–383.

The Marine Benthic Flora of Southern Australia Part I complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
Part I
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

Illustration in Womersley Part I, 1984: FIG. 72.

Figure 72 image

Figure 72   enlarge

Fig. 72. Microdictyon umbilicatum(ADU, A51823). A. Thallus. B. Branching pattern of the net. C. Detail of branching of the net.

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