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Rhodymenia verrucosa Womersley, sp. nov.

Phylum Rhodophyta – Class Florideophyceae – Order Rhodymeniales – Family Rhodymeniaceae

Thallus (Fig. 27A, B) medium to dark red-brown, cartilaginous, 3–14 cm high, with one to a few complanately branched fronds, branching subdichotomous to alternate at intervals of 5–20 mm, branches (2–) 3–8 (–10) mm broad, 200–300 (–500) µm thick, usually thicker marginally, stipes terete to compressed, slender, simple or branched, 2–10 mm long, 0.3–1.0 mm thick. Holdfast crustose, 2–5 mm across, with one to a few fronds; epilithic. Structure multiaxial, developing a cortex (Fig. 27C, D) 1–2 cells broad, outer cells ovoid and 4–5 µm in diameter, grading abruptly to the medulla 3–5 (–10) cells broad, cells laxly arranged with intercellular spaces, ovoid, inner 2–3 cells often regularly arranged (Fig. 27C) and 45–90 µm in diameter, some cells with globular inclusions; stipe medulla 400–800 µm and 8–12 cells broad. Rhodoplasts discoid to elongate, ribbon like in inner cells.

Reproduction: Gametangial thalli probably dioecious. Carpogonial and auxiliary cell branches not observed. Carposporophytes (Fig. 27F) 600–900 µm across, with branched, elongate, fusion cells bearing a dense mass of ovoid carposporangia 15–25 µm in diameter. Basal nutritive tissue slight, erect filaments of stellate cells disintegrating early but some remaining. Cystocarps protuberant on the blade surfaces, mainly on one side and often clustered, sessile, basally constricted and the surface with prominent verrucose excrescences (Fig. 27E, F), 0.7–1.5 mm across, pericarp 180–360 µm (apart from the excrescences) and 10–20 cells thick, inner cells stellate, mid cells ovoid, outer cells more or less in anticlinal chains, ostiolate. Spermatangia not observed.

Tetrasporangia in sharply defined nemathecia (Fig. 27G, H) near branch ends, with the outer cortical cells becoming elongate and cutting off small outer cells; tetrasporangia (Fig. 30C) terminal, ovoid, 25–35 µm long and 12–22 µm in diameter, decussately or cruciately divided.

Type from Gabo I., Vic., 18 m deep (Shepherd, 17.ii.1973); holotype in AD, A43500, cystocarpic. Syntype from Gabo I., Vic., 13 m deep (Shepherd, 14.ii.1973); in AD, A43332, tetrasporangial and cystocarpic.

Selected specimens: Oedipus Point, West 1., S. Aust., 16 m deep (Shepherd, Dec. 1966; AD, A31142). Nora Creina, S. Aust., in channel between island and headland (Kraft 6220, 29.xii.1976; MELU, 38378). Cape Buffon, S. Aust., 2 m deep (Kildea & Collings, 27.ix.1992; AD, A62801). Warrnambool, Vic., drift (Kraft 7979 & Herrington, 6.xi.1989; MELU, 38371). Bicheno, Tas., 20–22 m deep (Kraft 9378, 18.xii.1992; MELU). Marion Bay, Tas., 3–5 m deep (Shepherd, 13.ii.1970; AD, A35599). Fluted Cape, Bruny I., Tas., 16 m deep (Shepherd, 10.ii.1972; AD, A41526).

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

Distribution: Althorpe Is, S. Aust., 15 m deep (Baker, 26.x.1993; AD, A64480). West I., S. Aust., to Gabo I., Vic., and eastern Tasmania.

Taxonomic notes: R. verrucosa is characterised by the prominently verrucose cystocarps which set it apart from all other described species of Rhodymenia. The medulla in young branches has two central cells which are more rounded and laxer as a tissue than in most species, and the inner layer of the pericarp also has more stellate cells than is usual in the genus. The above description of tetrasporangial nemathecia is based on two collections (the syntype and MELU, 38371) where tetrasporangial and cystocarpic plants are on the one sheet. Transverse sections of the thalli are similar and it is presumed that they belong to the one species.

References: The Marine Benthic Flora of Southern Australia Part IIIB

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (28 June, 1996)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIB. Gracilarialse, Rhodymeniales, Corallinales and Bonnemaisoniales
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIB 1996, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

Illustrations in Womersley Part IIIA, 1996: FIGS 27, 30C.

Figure 27 image

Figure 27   enlarge

Fig. 27. Rhodymenia verrucosa (A, C–F, AD, A43500; B, G, H, AD, A43332). A. Habit, cystocarpic plants. B. Habit, tetrasporangial plant on left, cystocarpic on right. C. Transverse section of young branch. D. Transverse section of older branch. E. Verrucose cystocarps. F. Section of cystocarp with verrucose pericarp. G. Surface view of tetrasporangial nemathecium. H. Sectional view of tetrasporangial nemathecium.

Figure 30 image

Figure 30   enlarge

Fig. 30. A. Cordylecladia furcellata (AD, A39609). Transverse section of cortex with carpogonial branch and probable auxiliary cell branch. B. Erythrymenia minuta (AD, A22254). Transverse section of cortex with developing intercalary sporangia. C. Rhodymenia verrucosa (AD, A43332). Transverse section of cortex with developing and mature tetrasporangia. D. Rhodymenia obtusa (AD, A63267). Transverse section of thallus with a carpogonial branch. E. Rhodymenia prolificans (AD, A49246). Transverse section of thallus post fertilization, with a carpogonial branch and proliferating auxiliary cell branch (auxiliary cell with a globular inclusion).

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