Electronic Flora of South Australia Species Fact Sheet

Dictyota naevosa (Suhr) J. Agardh 1848: 95.

Phylum Phaeophyta – Order Dictyotales – Family Dictyotaceae – Tribe Dictyoteae

Selected citations: De Toni 1895: 266. Kützing 1859: 13, pl. 31 fig. I.


Zonaria nervosa Suhr 1834: 723, fig. 4.

Thallus (Fig. 63B) medium to dark brown, occasionally light brown when fresh, usually 20–40 cm long with branches 1–2.5 (–3) cm broad, subdichotomously branched (2–) 5–10 cm apart, commonly with unbranched upper parts often 10–15 cm long, with rounded axils and apices; proliferations present only after damage. Holdfast of rhizoids and sometimes with a few, subterete, short, stolons; epilithic. Cortical cells (15–) 20–30 (–40) µm across, L/B I -2 (–3), with the medullary cell outlines usually conspicuous in dried specimens. Cortex forming compact, short, filaments of 2–6 cells in the central part very close to the base. Medulla monostromatic, rarely 2 cells thick very near the base. Hair tufts often more or less in lines across the branches, hairs 15–20 µm in diameter.

Reproduction: Tetrasporangia (Fig. 64E) 80–120 (–180) µm in diameter, grouped into elongate-ovoid sori mostly 2–4 mm long and 1–2 mm across, centred around hair tufts, often with other scattered sporangia. Sexual reproduction unknown.

Type from Algoa Bay, South Africa (Ecklon); in LD?

Selected specimens: Port Denison, W. Aust., 1–5 m deep on jetty (Kraft, 14.xii.1971; ADU, A41168). Mandurah, W. Aust., drift (Oberlander, 21.i.1961; ADU, A24711). Head of Great Australian Bight, S. Aust., drift ( Womersley, 4.6.1954; ADU, A19176). Point Sinclair, S. Aust., drift (Womersley, 25.i.1951; ADU, A13602 and 7.6.1954; ADU, A19577). Masillon I., Isles of St Francis, S. Aust., 13–18 m deep (Shepherd, 5.i.1971; ADU, A38015). Marion Bay, Yorke Pen., S. Aust., drift (Womersley, 9.iv.1950; ADU, A13134). Investigator Str., S. Aust., 31 m deep, 35°21'S, 137°17'E (Watson, 24.i.1970; ADU, A38394). Port Noarlunga, S. Aust., 24 m deep 5 km offshore (Ottaway, 3.ii.1981; ADU, A52097). Port Willunga, S. Aust., drift (Womersley, 24.iv.1948; ADU, A8370). Western R., Kangaroo I., S. Aust., drift (Womersley, 7.i.1946; ADU. A2988).

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

Distribution: Southern coast of South Africa.

In southern Australia, from Port Denison, W. Aust. to Port Willunga, S. Aust.

Taxonomic notes: D. naevosa is apparently a deep water species, known from the drift and to 31 m deep. It is the largest southern Australian species of Dictyota, and agrees well with Isaac specimens in ADU from South Africa, though less variable in width and colour. Near the base in large plants, the central part only develops filaments 2–6 cells long, forming a compact tissue, and occasional divisions of the medullary cells occur. These variations from Dictyota structure are not sufficiently distinctive to refer D. naevosa to a different genus. Distinctions between D. naevosa and D. diemensis are discussed under the latter species.


AGARDH, J.G. (1848). Species, Genera et Ordines Algarum. Vol. 1. (Gleerup: Lund.)

DE TONI, G.B. (1895). Sylloge Algarum omnium hucusque Cognitarum. Vol. 3. Fucoideae. pp. 1–638. (Padua.)

KÜTZING, F.T. (1859). Tabulae Phycologicae. Vol. 9. (Nordhausen.)

SUHR, J.N. von (1834). Uebersicht der Algen, welche von Hrn. Ecklon an der sudafricanischen Kiiste gefunden worden sind. Flora 1834, 721–735, 737–743, Plates I, II.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

Illustrations in Womersley Part II, 1997: FIGS 63B, 64E.

Figure 63 image

Figure 63   enlarge

Fig. 63. A. Dictyota prolifera (ADU, A28588). B. Dictyota naevosa (ADU, A19176). C. Dictyota dietnensis, broad form (ADU, A35639). D. Dictyota diemensis, narrow form (ADU, A56304).

Figure 64 image

Figure 64   enlarge

Fig. 64. A–D. Dictyota prolifera (A,B, ADU, A19576; C,D, ADU, A28588). A. Thallus with sporangial sori on opposite sides in concave undulations, with small proliferations. B. Transverse section of thallus with undivided sporangia. C. Thallus with male sori on opposite sides. D. Transverse section of male sorus with antheridia and paraphyses, and a young hair tuft from opposite surface. E. Dictyota naevosa (ADU, A13602). Transverse section of thallus with undivided sporangia. F. Dictyota diemensis, broad form (ADU, A35622). Transverse section of thallus with undivided sporangia. G. Dictyota diemensis, narrow form (ADU, A56304). Transverse section of thallus with undivided sporangia. H–M. Dictyota dichotoma (ADU, A26409). H. Surface view of branch with scattered sporangia and hair groups. I. Transverse section of thallus with sporangia. J. Surface view of branch with oogonial sori. K. Transverse section of thallus with an oogonial sorus. L. Surface view of an antheridial sorus with sterile peripheral paraphyses. M. Transverse section of thallus with an antheridial sorus.

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