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Dilophus robustus (J. Agardh) Womersley 1967: 213.

Phylum Phaeophyta – Order Dictyotales – Family Dictyotaceae – Tribe Dictyoteae


Dictyota robusta J. Agardh 1894a: 76.

Thallus (Fig. 67B) medium to dark brown, (5–) 10–20 cm long, dichotomously branched at intervals of (1–) 1.5–5 cm, branches (3–) 5–15 (–20) mm broad, usually increasing in width above points of branching, axils rounded, apices broad and usually truncate with a slightly depressed apical cell; proliferations absent except following damage. Holdfast rhizoidal; epilithic. Cortical cells 14–22 p.m across, L/B 1–4.5 (–2). Medulla in upper and mid parts of thallus (Fig. 68A) one cell thick centrally, 3–4 cells thick near the margins, in older parts (Fig. 68B) becoming 2 cells thick centrally; thickness centrally 120–160 µm, becoming 200–240 µm thick below, margins 240–320 µm thick; intracellular wall thickenings present in medullary cells of some thalli. Hair tufts scattered, hairs 16–24 µm in diameter.

Reproduction: Unknown.

Type from Port Phillip Heads, Vic. (Wilson); in Herb. Agardh, LD, 49152. Distribution: From Port Denison, W. Aust. to Port Phillip Heads, Vic.

Selected specimens: Port Denison, W. Aust., drift (Kraft 1881, 6.vii.1966; MELU). Two People Bay, W. Aust., drift (Kraft 1743, 30.vi.1966; MELU, tetrasporangial). D'Entrecasteaux Reef (E. of Head of Great Australian Bight), S. Aust., 15–20 m deep (Shepherd, 27.iii.1980; ADU, A52149). Pearson I., S. Aust., 50 m deep (Shepherd, 9.i.1969; ADU, A33876). Elliston, S. Aust., drift (Womersley, 13.i.1951; ADU, A13432). Seal Beach, Kangaroo I., S. Aust., drift (Womersley, 21.i.1965; ADU, A28590). Amphitheatre Rock, West I., S. Aust., 13 m deep (Shepherd, 1.i.1969; ADU, A33250).

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

Taxonomic notes: Dilophus robustus is a deep water species off open coasts, known from 10 to 50 m deep. It is by far the broadest of the single-medullary layered species, but with a thicker marginal and basal medulla.


AGARDH, J.G. (1894a). Analecta Algologica. Cont. I. Acta Univ. lund. 29, 1–144, Plates 1, 2.

WOMERSLEY, H.B.S. (1967). A critical survey of the marine algae of southern Australia. II. Phaeophyta. Aust. J. Bot. 15, 189–270.

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 67B, 68A,B.

Figure 67 image

Figure 67   enlarge

Fig. 67. A. Glossophora nigricans (ADU, A33254). B. Dilophus robustus (ADU, A28590). C. Dilophus angustus (ADU, A19885). D. Dilophus marginatus (ADU, A56810).

Figure 68 image

Figure 68   enlarge

Fig. 68. A,B. Dilophus robustus (ADU, A28590). A. Transverse section of upper thallus. B. Transverse section of lower thallus. C,D. Dilophus angustus ( C, ADU, A18573; D, ADU, A24519). C. Transverse section of mid thallus. D. Surface view of tetrasporangial thallus. E–G. Dilophus marginatus (ADU, A56810). E. Transverse section of upper thallus. F. Transverse section of mid thallus with tetrasporangia. G. Transverse section of thallus close to holdfast, with rhizoids. H–K. Dilophus tener (H,I, ADU, A30323; J, ADU, A38154; K, ADU, A34095). H. Upper branches with tetrasporangia and hair tufts. I. Transverse section of young thallus with undivided sporangia. J. Transverse section of mid thallus. K. Transverse section of thallus close to the base.

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