Electronic Flora of South Australia Species Fact Sheet

Pachymenia orbicularis (Zanardini) Setchell & Gardner 1934: 134.

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Halymeniaceae


Gigartina orbicularis Zanardini 1874: 501. J. Agardh 1876: 205. De Toni 1897: 227.

Pachymenia stipitata J. Agardh 1890a: 16. De Toni 1905: 1577.

P. apoda J. Agardh 1890a: 14. De Toni 1905: 1576.

P. sessilis J. Agardh in Wilson 1892: 184 (nomen nudum).

Epiphloea grandifolia J. Agardh 1890a: 20. De Toni 1905: 1578.

Thallus (Fig. 64A) medium to very dark red to red-brown, fading to yellow-red, usually uniformly coloured but sometimes mottled, drying cartilaginous and partly to largely adhering to paper, 20–90 cm high, foliose, complanate and usually divided to near the base with cuneate to ovate fronds 5–30 cm broad, 0.5–1 mm thick above, 1–2 mm thick below, with the margin smooth to irregularly indented or slightly spinous, occasionally with marginal proliferations usually 2–8 cm long and 0.5–2 cm broad, basally constricted; stipe usually long and tapering, occasionally short below a broad frond. Holdfast discoid, robust, 2–8 mm across; epilithic. Structure (Fig. 64B) of a thick cortex 10–20 cells broad, with an outer cortex 80–120 µm thick of compact anticlinal rows of 8–15 elongate cells, outer cells 3–4 µm in diameter and L/D 3–4 (the inner ones slightly broader), branched every 2–5 cells, and an inner cortex of irregularly lobed, separated, cells 10–15 µm across, becoming slightly stellate. Medulla broad, densely and irregularly filamentous with broader and slenderer (rhizoidal) filaments, refractive ganglionic cells present or absent.

Reproduction: Sexual thalli dioecious. Carpogonial branch ampullae (Fig. 63D) in the outer cortex, with few, more or less erect, secondary filaments. Auxiliary cell ampullae (Fig. 63E) prominent, 60–100 µm across, with numerous secondary and tertiary filaments of ovoid cells, converging above and cutting off from their mid and upper cells short to medium chains of ovoid cells of fourth and fifth orders. Carposporophytes largely within the medulla, 150–200 µm across, compact, carposporangia ovoid 8–12 µm across. Involucre moderate to dense, 30–40 µm and several filaments thick, at first lax but becoming compacted, with the ampullary filaments separating the outer cortical filaments and leaving an ostiole. Spermatangia not observed.

Tetrasporangia (Fig. 63F) scattered in the outer cortex, cut off from cells 3–6 deep and lying just below the surface, 15–25 µm long and 8–12 µm in diameter, cruciately divided.

Type from Port Phillip, Vic. (Mueller); holotype in Herb. Zanardini, Museo Civico di Storia Naturale, Venice.

Selected specimens: Garden I., W. Aust., 21 m deep (Kirkman, 28.iv.1980; AD, A51074). Safety Bay, W. Aust., drift (Womersley, 18.viii.1979; AD, A50768). Elliston, S. Aust., 17 m deep outside bar (Shepherd, 12.v.1971; AD, A38675). Cable Hut Bay, Yorke Pen., S. Aust., drift (Womersley, 15.x.1988; AD, A59160). Tiparra Reef, S. Aust., 15 m deep (Shepherd, 11.i.1978; AD, A49418). Port Elliot, S. Aust., drift (Womersley, 24.vii.1949; AD, A11130). Vivonne Bay, Kangaroo I., S. Aust., drift (Womersley, 2.i.1949; AD, A10677) and 3 m deep on jetty piles (Kraft & Min Thein, 4.xii.I971; AD, A41398). Pelorus I., S of Kangaroo I., S. Aust., 25 m deep (Branden, 19.vi.1991; AD, A61384). 400 m off Cape Buffon, S. Aust., 5 m deep (Collings, 25.i.1991; AD, A61237). Off Middle Point, Cape Northumberland, S. Aust., 24 m deep (Shepherd, 19.iii.1974; AD, A44953). Port MacDonnell, S. Aust., drift (Womersley, 15.iv.1959; AD, A22982). Dutton Bay, Portland, Vic., drift (Womersley, 13.iv.1959; AD, A22682). Cape Woolamai, Vic., 16 m deep (Watson, 30.iii.1970; AD, A35837). Adventure Bay, Bruny I., Tas., drift (Wollaston & Mitchell, 28.ii.1964; AD, A27884).

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

Distribution: Garden I., W. Aust. to Cape Woolamai, Vic., and around Tasmania.

Taxonomic notes: P. orbicularis is very similar in habit to the type species, P. carnosa, from South Africa, but differs in that the anticlinal cortical filaments are of elongate cells (ovoid in the latter) and the inner cortical cells are larger. "Rays" from the base of the carposporophyte, as described by Simons & Hewitt (1976) for P. carnosa, have not been observed in P. orbicularis.

P. orbicularis appears to be the earliest name for this rather variable species, with AD, A22682 agreeing well in form with the type. It is, however, desirable that detailed studies be carried out on the type in Venice. P. stipitata J. Agardh (type from "Adelaide", holotype in Herb. Agardh, LD, 22485) is a more elongate form with a tapering cuneate stipe, while P. apoda J. Agardh [type from Puebla Bay (NE of Torquay), Vic. (Wilson 101, 18.ix.1886; in Herb. Agardh, LD, 22427)] was given the ms. name of P. sessilis J. Agardh and is similar to P. orbicularis in form; Epiphloea grandifolia J. Agardh [type from Port Phillip Heads, Vic. (Wilson; Herb. Agardh, LD, 22493)] is an elongate, broad, form a metre or so long. All these are within the range of form of P. orbicularis.

P. orbicularis is a deep water and fairly common alga on south-east Australian coasts, being variable in form, especially in the degree of frond broadening from the stipe, and also in the development of the cortex and the presence or not of refractive ganglionic cells. Plants from the western part of its range (e.g. Kangaroo I. and Western Australia) tend to be thinner and have more marginal foliose proliferations than plants from south-eastern coasts.


AGARDH, J.G. (1876). Species Genera et Ordines Algarum. Vol. 3, Part 1 - Epicrisis systematis Floridearum, pp. i-vii, 1–724. (Weigel: Leipzig.)

AGARDH, J.G. (1890a). Till algemes systematik. Acta Univ. lund. 26(3), 1–125, Plates 1–3.

DE TONI, G.B. (1897). Sylloge Algarum omnium hucusque Cognitarum. Vol. 4. Florideae. Sect. 1, pp. 1–388. (Padua.)

DE TONI, G.B. (1905). Sylloge Algarum omnium hucusque Cognitarum. Vol. 4. Florideae. Sect. 4, pp. 1523–1973. (Padua.)

SETCHELL, W.A. & GARDNER, N.L. (1934). De Gigartinis. Rev. Algol. 7, 131–138.

SIMONS, R.H. & HEWITT, F.E. (1976). Marine algae from southern Africa. 2. Morphology and taxonomy of five foliaceous Florideophyceae (Rhodophyta). Invest! Rep. Sea Fish. Brch S. Afr. 110, 1–46.

WILSON, J.B. (1892). Catalogue of algae collected at or near Port Phillip Heads and Western Port. Proc. R. Soc. Vict. 4, 157–190.

ZANARDINI, J. (1874). Phyceae Australicae novae vel minus cognitae. Flora (Regensburg) 57, 486–490, 497–505.

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

Author: H.B.S. Womersley & J.A. Lewis

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 63 D–F, 64A, B.

Figure 63 image

Figure 63   enlarge

Fig. 63. A–C. Gelinaria ulvoidea (A, B, AD, A60180; C, AD, A22674). A. Carpogonial branch ampulla within the cortex. B. Auxiliary cell ampulla. C. Transverse section of cortex with tetrasporangia. D–F. Pachymenia orbicularis (D, E, AD, A61237; F, AD, A11130). D. Carpogonial branch ampulla within the cortex. E. Auxiliary cell ampulla within the cortex. F. Transverse section of cortex with tetrasporangia.

Figure 64 image

Figure 64   enlarge

Fig. 64. A, B. Pachymenia orbicularis (A, AD, A61384, B, AD, A61237). A. Habit. B. Transverse section of thallus with a mature auxiliary cell ampulla. C–F. Aeodes nitidissima (AD, A27934). C. Habit. D. Transverse section of thallus with several auxiliary cell ampullae and one (on right) young cystocarp. E. Transverse section with an auxiliary cell ampulla with a 3-celled gonimoblast. F. Transverse section of cortex with tetrasporangia.

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