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Bornetia tenuis Baldock & Womersley 1968: 205.

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Bornetieae

Selected citations: Norris & Aken 1985: 60, fig. 22. Millar 1990: 412 figs 49E, F. Millar & Kraft 1993: 37. Silva et al. 1996: 383.

Thallus (Fig. 148B) tufted, dark red, 3–7 cm high, epilithic or epiphytic. Filaments subdichotomous at intervals of 2–3 cells, ecorticate, attached by rhizoids at the base. Structure. Cells linear, usually 200–250 µm in diameter and L/D 5–8. Cells multinucleate; rhodoplasts discoid.

Reproduction: Gametophytes dioecious. Procarp systems 2 (–3), produced in succession subapically on an adaxial, lateral fertile axis consisting of a larger basal cell (furcate apically) and 5–7 small cells (Fig. 150A); sometimes a separate larger basal cell is not cut off from the vegetative axis, but a constriction forms a basal region (Fig. 150B, C). Procarp systems each consist of a supporting cell bearing apically a sterile cell which often develops into a 2-celled non-functional carpogonial branch, and laterally a recurved, functional 4-celled carpogonial branch, and also a sterile periaxial which develops into a 2-celled non-functional carpogonial branch. Carposporangia terminal (Fig 148C), granular, clavate, densely cytoplasmic, with several vacuoles radiating from a single, central nucleus; 30–40 µm in diameter and L/D 1.7–1.9, radiating from a stellate fusion cell (Fig. 150D); carposporophyte surrounded by 1 (–2)-celled involucral branches, sometimes cells furcate apically (Fig. 150B), cut off from the basal and lower two cells of the fertile axis, or the lowest branch(es) may arise as prolongations of the basal region when no separate basal axial cell occurs (Fig. 150C). Spermatangial heads (Fig 148D) sessile, elongate, 70–81 µm in diameter and L/D 1.8–3, single and apical on the inner sides of oblong cells of lateral, condensed, subdichotomous branch systems produced in a 1/4 spiral pattern, the larger elongate, incurved terminal cells of which provide a basket-shaped involucre (Figs 148D, 150E); heads rarely exceeding the involucre.

Tetrasporangia sessile, in clusters of 1–4 on the inner sides of cells of subdichotomous, condensed, lateral branch systems (Fig. 148E, 150F), the terminal cells of which form incurved involucres as with spermatangial heads; globose, 60–65 µm in diameter, tetrahedrally divided.

Type from Grange Beach (Adelaide), S. Aust., drift (Baldock, 23.i.1965); holotype (tetrasporangial) and isotypes (tetrasporangial and male plants) in AD, A28632.

Selected specimens: Semaphore S. Aust., upper sublittoral on jetty piles (Nielsen, 16.iii.1968; AD, A32282). Victor Harbor, S. Aust., drift (Womersley, 2.xi.1965; AD, A29631).

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

Distribution: Adelaide metropolitan beaches, and Victor Harbor, S. Aust.; Port Phillip Bay, Vic. (Lewis 1983, p. 262). The preferred habitat appears to be relatively sheltered bays.

Taxonomic notes: B. tenuis vegetatively resembles small Anotrichium spp (Griffithsieae) in its fine, ecorticate, subdichotomous filaments, but is distinctive reproductively, particularly in the basket-shaped male and tetrasporangial structures.

B. tenuis was recorded from Coffs Harbour, N.S.W. (Millar 1990, p. 412, fig. 49E, F), and South India (Krishnamurthy & Thomas 1971, p. 36, figs. 15–18, 44, 45), although the cells in the latter record are less elongate. Norris & Aken (1985, p. 60, fig. 22) attributed this species to South Africa on the basis of single fertile male specimen, although the involucral cells were significantly smaller relative to the spermatangial heads in their specimen.


BALDOCK, R.N. & WOMERSLEY, H.B.S. (1968). The genus Bornetia (Rhodophyta, Ceramiaceae) and its southern Australian representatives, with a description of Involucrana gen. nov. Aust. J. Bot. 16, 197–216, Plates 1–4.

KRISHNAMURTHY, V. & THOMAS, P.C. (1971). Some new and interesting red algae from the Indian shores. Seaweed Res. Util. 1, 30–47.

LEWIS, J.A. (1983). Floristic composition and periodicity of subtidal algae on an artificial structure in Port Phillip Bay (Victoria, Australia). Aquatic Bot. 15, 257–274.

MILLAR, A.J.K. & KRAFT, G.T. (1993). Catalogue of marine and freshwater Red Algae (Rhodophyta) of New South Wales, including Lord Howe Island, South-western Pacific. Aust. Syst. Bot. 6, 1–90.

MILLAR, A.J.K. (1990). Marine red algae of the Coffs Harbour region, northern New South Wales. Aust. Syst. Bot. 3, 293–593.

NORRIS, R.E. & AKEN, M.E. (1985). Marine benthic algae new to South Africa. S. Afr. J. Bot. 51, 55–65.

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

Author: R.N. Baldock & H.B.S. Womersley

Publication: Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
©State Herbarium of South Australia, Government of South Australia

Illustrations in Womersley Part IIIA, 1998: FIGS 148 B–E, 150.

Figure 148 image

Figure 148   enlarge

Fig. 148. A. Bornetia binderiana (AD, A51011). Habit. B–E. Bornetia tenuis (B, D, E, AD, A28632; C, AD, A29631). B. Type. Habit of tetrasporangial plant. C. Carposporophyte showing stellate fusion cell. D. Spermatangial heads in a lateral, condensed branch system. E. Tetrasporangia in lateral, condensed branch systems. (B–E, as in Baldock & Womersley 1968, courtesy of Aust. J. Bot.)

Figure 150 image

Figure 150   enlarge

Fig. 150. Bornetia tenuis (A–D, AD, A29361; E, F, AD, A28632). A. Young fertile axis, showing origin of involucral branches and periaxial cells. B. Fertile axis with a mature procarp consisting of a supporting cell bearing a functional (4-celled) and non-functional (2-celled) carpogonial branch. C. Developing cystocarp, showing bifurcate involucral cell and constricted basal region. D. Carposporophyte with enlarging fusion cell and developing carposporangia. E. Development of axes which produce spermatangial heads in a lateral, condensed branch system. F. Young tetrasporangia borne on a lateral, condensed branch system. (All as in Baldock & Womersley 1968, courtesy of Aust. J. Bot.)
Note:Axial cells are numbered from base up to reflect continuing growth.

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