Electronic Flora of South Australia Species Fact Sheet

Dudresnaya australis J. Agardh ex Setchell 1912: 245, pl. 27, fig. 9.

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Dumontiaceae

Selected citations: J. Agardh 1899: 85. De Toni 1924: 559. Mitchell 1966: 215. Robins & Kraft 1985: 11, figs 16–43. Shepley & Womersley 1983: 207, figs 2A, 4.

Thallus (Fig. 68C) rose-red to dark red-brown, 5–16 cm high, erect and much branched, spreading, variable in robustness, mucilaginous, with a main axis 2–3 mm in diameter bearing irregularly radially arranged laterals to 3 or 4 orders, terete and tapering and 0.5–1 mm in diameter in lesser branchlets which are alternate to opposite. Holdfast discoid, 1–3 mm across; epiphytic on Amphibolis, Heterozostera or larger algae, or possibly epilithic. Structure uniaxial, with an apical cell dividing transversely and producing a row of discoid cells which become cylindrical axial cells 300–400 µm long and 50–250 µm in diameter when mature, with 4 (–6) periaxial cells each bearing tufted fascicles basally divided at each or most cells below, then unbranched and when mature gently tapering, usually 12–16 cells long with cells (5–) 8–14 µm in diameter and L/D 2–3 (–5). The outer medulla grades to the cortex and the outer cortical cells near branch apices bear long, slender, floridean hairs. Lateral branches arising from periaxial or inner cortical cells, first developing as unbranched primordia of 15–20 (–40) discoid cells. Young thallus branches usually show slight annulations corresponding to the periaxial whorls. Each periaxial cell also produces a descending rhizoid of elongate cells, each cell of which may produce a lateral branch system similar to and lying between the periaxial whorls, and resulting in a more continuous medulla and cortex. The descending rhizoids pass down over two or three axial cells and thus each axial cell becomes surrounded by 12–18 rhizoids, which ultimately enlarge to similar diameter as the axial cells and tend to obscure the latter. In the mature thallus, numerous secondary descending rhizoids develop from other cells of the periaxial laterals, forming an interwoven filamentous medulla.

Reproduction: Sexual thalli usually dioecious. Carpogonial branches (Fig. 69E) develop usually on periaxial cells of lateral thallus branches, 6–10 cells long with the upper 3 cells reflexed and cells 2 and 3 smaller; the basal or sub-basal cell frequently bears a single lateral cell (Fig. 69F). Following fertilization, an extension from the carpogonium fuses with cell 4 (Fig. 69F) and frequently extends to cell 5, and the resultant large fusion cell produces several connecting filaments each with a basal pit-connection. Auxiliary cell branches (Fig. 69G) develop from periaxial cells and also from basal cells of lateral branch systems developed from the descending rhizoids, and thus considerably outnumber the carpogonial branches. Auxiliary cell branches 11–20 cells long, with 3–5 mid cells larger and the central of these (often fifth from the base) is the smaller, compressed, auxiliary cell (Fig. 69G); the terminal 6–8 cells often taper and a sterile lateral cell may occur on the basal cell as in carpogonial branches. Nearly all auxiliary cells are contacted by connecting filaments (Fig. 69G) and two gonimoblast initials develop opposite the fusion side of the auxiliary cell. Carposporophytes (Fig. 69H) compact (initially two lobed), of different ages, scattered profusely in the outer medulla but scarcely swelling the thallus, 100–175 µm in diameter with most cells forming rounded to angular carposporangia 10–27 µm in diameter. Male gametophytes with spermatangia formed in dense clusters (Fig. 69I) from 1–4 terminal and subterminal cells of the outer cortex.

Tetrasporophytes have denser rhizoidal development than gametophytes, and this obscures the basic whorled branch pattern to a greater extent. Tetrasporangia large, zonately divided (Fig. 69J), 25–45 (–50) µm long and 12–20 µm in diameter, terminal or lateral on outer medullary cells of both the periaxial branch systems and those arising from the descending rhizoids. Further tetrasporangia may arise from short branches originating below the earlier tetrasporangia.

Type from Port Phillip, Vic. (Wilson 28, 23.i.1888); lectotype in Herb. Agardh, LD, 34730; isolectotypes in MEL, 504444 and BM.

Selected specimens: King George Sound, W. Aust. (Harvey, Tray. Set. 325). Pearson I., S. Aust., 15 m deep (Shepherd, 8.i.1969; AD, A33940). Point Avoid, S. Aust., drift (Christophel, 7.xii.1976; AD, A47821). Tiparra reef, Spencer Gulf, S. Aust., 6 m deep on Amphibolis (Shepherd, 29.i.1972; AD, A41865). Investigator Strait, S. Aust., 33 m deep (Watson, 20.i.1971; AD, A38583). Northern Spencer Gulf, S. Aust., 8 m deep (Shepherd, 4.ix.1973; AD, A44148). Off Troubridge I., S. Aust., 24 m deep (Shepherd, 5.ii.I969; AD, A33861, male). Inside Tapley Shoal, S. Aust., 10 m deep (Shepherd, 2.ii.1969; AD, A33469). American R. inlet, Kangaroo I., S. Aust., drift at jetty (Womersley, 31.x.1966; AD, A30830). Western Port, Vic. (Wilson, 5.ii.1894; MEL, 5333). Hinders, Vic., drift (Womersley & Mitchell, 18.i.1967; AD, A31501). Low Head, Tas. (Perrin 325 & Lucas, Jan. 1930; BM).

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

Distribution: King George Sound, W. Aust., to Western Port, Vic., and the N coast of Tasmania.

Taxonomic notes: D. australis is a sublittoral species known from 5 to 33 m deep and is commonly epiphytic on the seagrass Amphibolis, but also on the brown alga Caulocystis.

D. australis was first recognised but not formally described by J. Agardh (1899, p. 85, footnote). It is closely related to the type species (D. verticillata) but differs (Robins & Kraft 1985, p. 13) in the nature of the indeterminate axis primordia and details of the branch fascicles.


AGARDH, J.G. (1899). Analecta Algologica. Cont. V. Acta Univ. lund. 35, 1–160, Plates 1–3.

DE TONI, G.B. (1924). Sylloge Algarum omnium hucusque Cognitarum. Vol. 6. Florideae. (Padua.)

MITCHELL, E.A. (1966). The southern Australian genera of the Dumontiaceae (Rhodophyta). Nova Hedwigia 11, 209–220, Plates 22–26:2.

ROBINS, P.A. & KRAFT, G.T. (1985). Morphology of the type and Australian species of Dttdresnaya (Dumontiaceae, Rhodophyta). Phycologia 24, 1–34.

SETCHELL, W.A. (1912). Algae novae et minus cognitae, I. Univ. Calif Pubis Bot. 4, 229–269.

SHEPLEY, E.A. & WOMERSLEY, H.B.S. (1983). The Dumontiaceae (Cryptonemiales: Rhodophyta) of southern Australia. Trans. R. Soc. S. Aust. 107, 201–217.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 January, 1994)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIA, Bangiophyceae and Florideophyceae (to Gigartinales)
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIA 1994, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

Illustrations in Womersley Part IIIA, 1994: FIGS 68C, 69 E–J.

Figure 68 image

Figure 68   enlarge

Fig. 68. A. Acrosymphyton taylorii (AD, A38045). Habit. B. Dasyphloea insignis (AD, A43343). Habit. C. Dudresnaya australis (AD, A33469). Habit. D, E. Kraftia dichotoma (D, AD, A52844; E, AD, A43937). D. Habit. E. An erect multiaxial axis arising from the crustose base on Amphibolis stem. F. Gibsmithia womersleyi (MELU, K7654, holotype). Habit. [A–E as in Shepley & Womersley 1983; F as in Kraft 1986.]

Figure 69 image

Figure 69   enlarge

Fig. 69. A–D. Acrosymphyton taylorii (AD, A38045). A. Cortical branch system with a young auxiliary cell branch. B. Mature carpogonial branch and adjacent auxiliary cell branch. C. A carpogonial branch with a terminal lateral cell acting as an auxiliary cell with a connecting filament and 2-celled gonimoblast. D. A young carposporophyte surmounting an auxiliary cell branch. E–J. Dudresnaya australis (E–H, J, AD, A30830; I, AD, A33861). E. Mature carpogonial branch with spermatia on trichogyne. F. Post-fertilization carpogonial branch producing connecting filaments. G. Auxiliary cell with connecting filaments and first gonimoblast cell. H. Mature carposporophyte on auxiliary cell filament. I. Spermatangial branch in sectional view. J. Tetrasporangia on cortical filaments. [A–J after Shepley & Womersley 1983.]

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