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Plocamium patagiatum J. Agardh 1894: 133.

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Plocamiaceae

Selected citations: De Toni 1900: 601; Guiler 1952: 90. Lucas 1909: 35. Lucas & Perrin 1947: 215. May 1965: 372. Womersley 1971a: 15, figs 12–16.

Thallus (Fig. 127A) robust, to 10–30 cm high. Erect axes 3–4 (–5) mm broad, fairly regularly branched. Ramuli in alternate pairs, the upper ramulus commonly remaining dormant, otherwise developing into a long straight lateral bearing regular ramuli with occasional further laterals; the upper ramulus of each pair usually 2–2.5 mm broad and 3–5 mm long, digitate with divisions more on the abaxial side; lower ramulus simple, entire, rarely serrate, subulate, acuminate (1–) 1.5–2.5 (–3) mm long and 0.5–1 mm broad at its base.

Reproduction: Sexual thalli dioecious. Cystocarps (Fig. 127B) 1–2 (–3) in axils of upper or lower ramuli, globular and smooth, 0.75–1 (–1.5) mm in diameter, with a pedicel 0.2–1 times as long as the cystocarp and sometimes bearing abortive cystocarps on branches of the pedicel. Spermatangia covering the surface of much divided branchlets (Fig. 127C) forming dense, globular clusters to 0.5 mm high in the axils of ramuli.

Stichidia in dense, globular clusters in the axils of ramuli (Fig. 127D); individual stichidia basally branched only (Fig. 127E), oblong and swollen where bearing tetrasporangia, on a narrower stalk, 300–400 (–500) µm long and (100–) 120–150 (–170) µm broad. Tetrasporangia in two series, 75–100 µm long and 40–60 µm in diameter, zonately divided.

Lectotype from Encounter Bay, S. Aust. (Hussey); in Herb. Agardh, LD, 28174.

Selected specimens: Nuyts Reef, S. Aust., 30 m deep (Shepherd, 27.iii.1980; AD, A52338). 4 km W of Waldegrave I., S. Aust., 30 m deep (Branden, 3.vii.1987; AD, A57587). Topgallant I., S. Aust., 35 m deep (Branden, 2.vii.1987; AD, A57567). Port Elliot, S. Aust., drift (Womersley, 23.v.1953; AD, A18720). Whale Point, West I., S. Aust., 13 m deep (Shepherd, June 1966; AD, A30568). Pelorus I., S of Kangaroo I., S. Aust., 10–30 m deep (Branden, 19.vi.1991; AD, A61397). Robe, S. Aust., 3–6 m deep (Baldock, 15.v.1967; AD, A31492). Double Corner Beach, Portland, Vic., drift (Beauglehole, 22.vi.1952; AD, A21660). Cape Woolamai, Vic., 15–18 m deep (Goldsworthy & Berthold, 16.ii.1990; AD, A60188). Tamar R. mouth, Tas., 8–10 m deep (Blackman, 28.iv.1979; AD, A58532). Port Arthur, Tas. (Castray; NSW).

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

Distribution: Nuyts Reef, S. Aust. to Cape Woolamai, Vic. and around Tasmania. Found on coasts of strong wave action and known from depths of 10–26 m.

Taxonomic notes: P. patagiatum was not distinguished from P. mertensii until 1894, and until then had probably been included under the latter. However, its distribution is restricted compared to that of P. mertensii which occurs all along southern Australia, and it differs clearly in the form and size of the stichidia (which are shorter, stouter and more clavate than in P. mertensii) and usually in the habit and form of the upper and lower ramuli. In contrast to P. mertensii, the upper ramulus of P. patagiatum is broadly digitate and often remains dormant and the lower ramulus remains undivided. A few sterile specimens appear to be intermediate in form between these two species but tetrasporangial specimens are readily distinguished.


AGARDH, J.G. (1894). Analecta Algologica. Cont. II. Acta Univ. lund. 30, 1–98, Plate 1.

DE TONI, G.B. (1900). Sylloge Algarum omnium hucusque Cognitarum. Vol. 4. Florideae. Sect. 2, pp. 387–776. (Padua.)

LUCAS, A.H.S. & PERRIN, F. (1947). The Seaweeds of South Australia. Part 2. The Red Seaweeds. (Govt Printer: Adelaide.)

LUCAS, A.H.S. (1909). Revised list of the Fucoideae and Florideae of Australia. Proc. Linn. Soc. N.S.W. 34, 9–60.

MAY, V. (1965). A census and key to the species of Rhodophyceae (red algae) recorded from Australia. Contr. N.S.W. natn. Herb. 3, 349–429.

WOMERSLEY, H.B.S. (1971a). The genus Plocamium (Rhodophyta) in southern Australia. Trans. R. Soc. S. Aust. 95, 9–27.

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.

Illustration in Womersley Part IIIA, 1994: FIG. 127.

Figure 127 image

Figure 127   enlarge

Fig. 127. Plocamium patagiatum (AD, A30568). A. Habit. B. Branch with axillary cystocarps. C. Cluster of spermatangial branches. D. Branch with compact clusters of stichidia. E. Stichidia. [A–E as in Womersley 1971.]

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