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Pterocladia rectangularis (Lucas) Womersley & Guiry, comb. nov.

Phylum Rhodophyta – Class Florideophyceae – Order Gelidiales – Family Gelidiaceae


Gelidium rectangulare Lucas 1931: 407, pl. 23 fig. 1. Lucas & Perrin 1947: 144.

Thallus (Fig. 40D) medium to dark red, cartilaginous, forming erect tufts (5–) 10–25 (–30) cm high, with one to several pinnate to bipinnate (rarely tripinnate) axes, with pinnae and pinnules arising in close, regular series almost at right angles to the parent branch, becoming denuded below. Axes strongly compressed, linear, 1.5–2.5 mm broad throughout their length, thickened near the thallus base and above 600–800 µm thick, with occasional adventitious pinnae from the face of the lower axes. Pinnae 5–15 mm long, 0.5–1 (–1.5) mm broad (BIT 4–8), slightly constricted basally with some becoming indefinite laterals to 10 cm long. Pinnules similar to young pinnae, (3–) 5–8 mm long and 400–800 µm broad, basally constricted and usually tapering above, in regular close series separated usually by 0.7–1.5 times their basal width. Holdfast discoid-conical, 1–5 mm across, becoming fibrous; epilithic. Structure. Cortex 2–3 cells thick, outer cortical cells with the protoplast 3–5 µm across in surface view, walls moderately thick; medulla of elongate cells with many hyphae in older parts; rhizines profuse, mainly in outer medulla in young and mid thallus, throughout medulla in older axes.

Reproduction: Fertile ramuli borne on margins of pinnules. Cystocarps (Fig. 40E) single, subterminal on ramuli, swollen, 250–350 µm across, unilocular with a single prominent ostiole, 60–100 µm in diameter, in the raised pericarp; carposporophyte (Fig. 40F) broad-based with carposporangia in short chains maturing apically, clavate to ovoid, 18–25 µm in diameter. Spermatangial sori covering ends or upper halves of terete to slightly compressed ramuli 1–1.5 mm long and 150–250 µm in diameter, spermatangia cut off directly from outer cortical cells, 4–6 µm long and about 1 µm in diameter, forming terminal subspherical spermatia about 1 µm in diameter.

Tetrasporangial stichidia (Fig. 41K) short-stalked, terete to slightly compressed, becoming swollen terminally or centrally, 0.5–1.5 mm long and 100–150 (–200) µm broad. Tetrasporangia arising acropetally, derived from cortical cells and lying in the outer medulla and inner cortex, ovoid, 60–100 µm in diameter, decussately cruciately divided.

Type from Flinders Bay, W. Aust. (Lucas, Sept. 1928); lectotype in Herb. Lucas, NSW.

Selected specimens: Safety Bay, W. Aust., drift (Levring, 14.vii.1948; AD, A59041). Wyadup (S of Yallingup), W. Aust., drift (Royce 625, 4.vi.1950; AD, A15474). Eyre, W. Aust., drift (Woelkerling, 22.xi.1968; AD, A34231). Point Fowler, S. Aust., 2.5 m deep (Shepherd, 28.iii.1980; AD, A52239). Port Le Hunte (Point Sinclair), S. Aust. (Chambers, Nov. 1929; Herb. Lucas, NSW; AD, Al2224). Point Sinclair, S. Aust., in deep pools (Womersley, 26.i.1951; AD, A14009 -"Marine Algae of southern Australia" No. 78) and (Womersley, 8.ii.1954; AD, A 19549). Near Isles of St Francis, 37 m deep (Symonds, 23.x.1973; AD, A44250).

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

Distribution: Safety Bay, W. Aust., to the Isles of St Francis, S. Aust., usually in deep water or shaded pools.

Taxonomic notes: P. rectangularis is a distinctive species with its strict complanate pinnate branching, in the size of the compressed axes, pinnae and pinnules, their branching at slightly less than right angles, and the marginal series of fertile ramuli. The first cystocarpic plant known (AD, A59041) has the distinctive unilocular, single ostioles characteristic of Pterocladia, so this species is here transferred to this genus.


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

LUCAS, A.H.S. (1931). Notes on Australian marine algae. VI. Proc. Linn. Soc. N.S.W. 56, 407–411, Plates 23–27.

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

Author: H.B.S. Womersley & M.D. Guiry

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 40 D–F, 41K.

Figure 40 image

Figure 40   enlarge

Fig. 40. A, B. Pterocladia lucida (A, B, AD, A32644). A. Habit. B. Section through cystocarp showing entangled filaments forming a broad base to the carposporophyte, carposporangia and one ostiole. C. Pterocladia capillacea (AD, A22897). Habit. D–F. Pterocladia rectangularis (D, AD, A34231; E, F, AD, A59041). D. Habit. E. Cystocarps with prominent ostioles. F. Carposporophyte with secondary cell row and carposporangia (upper pericarp wall displaced).

Figure 41 image

Figure 41   enlarge

Fig. 41. A–E. Pterocladia lucida (AD, A32644). A. Habit, with tetrasporangial sori. B. Transverse section of thallus. C. Cystocarp with four ostioles. D. Transverse section with elongate spermatangial initials. E. Transverse section of tetrasporangial sorus. F–J. Pterocladia capillacea (AD, A22897). F. Branch with elongate cystocarps, the central one with two ostioles. G. Cross section of cystocarp, with the carposporophyte tufted around the axial cell, elongate cells connecting to the pericarp, and single ostiole. H. Transverse section of thallus. I. Branch with tetrasporangial sori. J. Cross section of tetrasporangial sorus. K. Pterocladia rectangularis (AD, A14009). Branch with tetrasporangial stichidia.

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