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Electronic Flora of South Australia Family Fact Sheet
Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae
Thallus subdichotomously to unilaterally branched, or primarily prostrate with several erect filaments arising from a creeping filament, ecorticate, attached by rhizoids from the basal cell(s); cells elongate, cylindrical, usually relatively large (2–3 mm long); gland cells absent. Cells multinucleate, with crystalline inclusions; rhodoplasts discoid, numerous, scattered or in chains.
Reproduction: Gametophytes dioecious. Female axis lateral, consisting of a larger basal cell and 5–6 (–8) small cells. Procarp systems 2 (–3), arising successively from subapical cells, each consisting of a supporting cell bearing a terminal sterile cell often dividing to form a 2-celled non-functional carpogonial branch, and a lateral, functional 4-celled carpogonial branch; a further sterile periaxial cell opposite the supporting cell, often dividing to form a 2-celled non-functional carpogonial branch. Following fertilization, further axial cell development usually ceases and the supporting cell divides so that the auxiliary cell is intercalated between sterile cells and residual supporting cell; fusion cell incorporating the auxiliary cell, residual supporting cell, lower gonimoblast cells, and possibly the axial cell at the level of the fertilized procarp, becoming stellate and bearing terminal, clavate carposporangia on slender processes. Involucral branches arising from the large basal and lower 2 small cells of the fertile axis and surrounding the carposporophyte in a condensed 1/4 spiral pattern, forming a characteristic basket-shaped structure. Spermatangial heads ovoid to elongate, sessile, borne singly and unilaterally on the inner side of subdichotomous branches of lateral, basket-like, condensed systems tending branching in a 1/4 spiral pattern.
Tetrasporangia borne singly or more commonly in clusters in similar condensed branch systems to the spermatangial heads, sessile (except possibly B. secundiflora), tetrahedrally divided.
Life history triphasic with isomorphic gametophytes and tetrasporophytes.
Type (and only) genus: Bornetia Thuret 1855:159.
Taxonomic notes: A monogeneric tribe of 5 species; the type from Mediterranean and European coasts, B. binderiana from southern Australia, B. tennis from southern Australia and possibly South India and South Africa, B. repens from South Africa, (Stegenga 1985b, p. 163), and B. californica from Pacific North America (Abbott 1971, p. 349).
The establishment of the tribe, represented solely by Bornetia was presaged by Baldock & Womersley (1968, p. 209).
The position of Bornetia within the Ceramiaceae is problematic. The several non-functional carpogonial branches of 2 cells and functional ones of 4 cells, associated with procarps produced successively along the fertile axis, resembles the Wrangelieae developmental line proposed by Kylin (1930, p. 76). However, Bornetia lacks whorl-branchlets, fertile procarps are initiated subapically and supporting cells are periaxial cells and not axial cells; these features place it closer to the Ceramieae developmental line.
Superficially, Bornetia resembles the Griffithsieae because of its large, uniseriate, multinucleate cells, subdichotomous branching, and the basket-shaped involucre around carposporophytes; several species have been ascribed previously to Griffithsia. Bornetia lacks synchronous branchlets which Millar (1986, p. 95) considers unique to the Griffithsieae; reproductively, Bornetia is closer to the Sphondylothamnieae (as defined by Gordon 1972, p. 47) in its extended fertile axis, and large gonimoblast fusion cell bearing terminal carposporangia. However, Bornetia differs significantly from the Sphondylothamnieae: it lacks whorl branchlets, has an extended female axis of 6 (–8) cells with 2 (–3) procarp systems bearing non-functional carpogonial branches, lacks an inner involucre about the carposporophyte and bears spermatangial heads and tetrasporangia in lateral, condensed, subdichotomous branch systems.
Kylin (1956, p. 370) and Hommersand (1963, p. 333) characterised the Spermothamnieae, in which they included Bornetia, by the presence of terminal carposporangia on the fusion cell. Members of this tribe are typically small, often epiphytic with prostrate axes which may be intermingled with filaments of host plants, and although similar to Bornetia in lacking whorl-branchlets, cells are small with fewer nuclei. This contrasts with the robust thalli, free prostrate axes and relatively large cells with numerous nuclei of Bornetia. The involucre surrounding the carposporophyte in the Spermothamnieae as defined by Gordon (1972, p. 112) develops from sub-hypogenous or hypogenous cells whereas in Bornetia it arises from 3 cells (large basal and lower 2 small cells of the fertile axis). In the Spermothamnieae, procarps are single and invariably subapical, and 2 auxiliary cells may be produced. The successive development of subapical procarp systems along a potentially indeterminate axis in Bornetia is a unique feature sufficient to separate it from the Spermothamnieae.
References:
ABBOTT, I.A. (1971). On some Ceramiaceae (Rhodophyta) from California. Pacif. Sci. 25(3), 349–356.
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.
GORDON, E.M. (1972). Comparative morphology and taxonomy of the Wrangelieae, Sphondylothamnieae and Spermothamnieae (Ceramiaceae, Rhodophyta). Aust. J. Bot. suppl. 4, 1–180.
HOMMERSAND, M.H. (1963). The morphology and classification of some Ceramiaceae and Rhodomelaceae. Univ. Calif Pubis. Bot. 35(2), 165–366.
KYLIN, H. (1930). Über die entwicklungsgeschichte der Florideen. Lunds Univ. Årsskr. N.F. Avd. 2, 26 (6), 1–104.
KYLIN, H. (1956). Die Gattungen der Rhodophyceen. (Gleerups: Lund.)
MILLAR, A.J.K. (1986). Baldockia verticillata (Griffithsieae, Ceramiales), a new red algal genus and species from eastern Australia. Phycologia 25(1), 87–97.
STEGENGA, H. (1985b). A new species of Bornetia (Rhodophyta, Ceramiaceae) from southern Africa. Br. phycol. J. 20, 163–168.
THURET, G. (1855). Note sur un nouveau genre d'algues de la famille des Floridées. Mem. Soc. sci. nat. Cherbourg 3, 155–160, Plates 1, 2.
The Marine Benthic Flora of Southern Australia Part IIIC complete list of references.
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
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