Electronic Flora of South Australia Family Fact Sheet

ORDER GELIDIALES Kylin 1923: 132

Phylum Rhodophyta – Class Florideophyceae

Thallus usually much branched bi- or tripinnately or irregularly, with a basal discoid, hapteroid or stoloniferous holdfast, branches terete to (usually) flat, cartilaginous. Cell walls containing agar; pit-plugs with a single cap layer. Growth by transverse division of a single apical cell, with each axial cell bearing two opposite periaxial cells producing lateral second-order filaments, which in turn produce opposite pairs of third-order filaments more or less at right angles to the axial and second-order filaments. Structure of a central axis and usually rows of second-order cells, surrounded by a core of elongate medullary cells derived from the apical and inner cortical cells, with numerous secondary pit-connections, in many species also with hyphae, and in all genera (none or very few in Gelidiella) with thick-walled (very narrow lumen) rhizines in the medulla (often dense in the outer medulla and/or inner cortex); cortex 2–5 cells thick, with anticlinal rows of ovoid cells, each with several small rhodoplasts without pyrenoids.

Reproduction: Sexual plants dioecious, rarely monoecious. Carpogonia and spermatangia usually formed on small branchlets or ramuli, or near the ends of branches. Carpogonia lateral and sessile, or intercalary, on inner cortical cells, usually with short, branched, nutritive filaments of ovoid cells developed from adjacent cells. Following fertilization the carpogonium enlarges, becomes multinucleate, and usually forms processes producing uninucleate gonimoblast initials and the much-branched gonimoblast forming carposporangia singly or in short chains; fusions occur between cells of the gonimoblast and the nutritive filaments, but in many species darkly staining nutritive filaments are visible in mature cystocarps. Cystocarps swollen, unilocular with 1 (–4) ostioles or bilocular with a central partition and an ostiole on each side; sterile inner cortical ("arachnoid") filaments of elongate cells usually extend through the cavity of the cystocarp; pericarp wall several cells thick. In Capreolia, stellate structures on the surface of female plants after fertilization develop directly into tetrasporophytes. Spermatangial initials replacing or cut off from surface cortical cells, elongate, dividing terminally to form one or more spermatangia, formed in sori on smaller branches or ramuli.

Tetrasporangia (rarely quadrinucleate bisporangia) borne laterally on cells of cortical filaments, becoming embedded in inner cortex or outer medulla, regularly or irregularly cruciately or decussately divided. Rhizines absent or rare in stichidia.

Life history triphasic with isomorphic gametophytes and tetrasporophyte, or heteromorphic and diphasic without the carposporophyte generation (Capreolia).

Taxonomic notes: The Gelidiales has included two families, the Gelidiaceae and the Gelidiellaceae Fan (1961, p. 317). The latter family contains Gelidiella only and is distinguished by lack of (or very few) rhizines. Maggs & Guiry (1987) have shown this feature to be inadequate for recognition of a separate family for Gelidiella, but Santelices (1990) and Norris (1992b) prefer keeping both families.

Dixon (1961) and Dixon & Irvine (1977b, p. 125) include the Gelidiales within the Nemaliales, but the studies of Pueschel & Cole (1982), Hommersand & Fredericq (1988) and Santelices (1990) support recognition of it as a separate order; the latter authors review the order. Norris (1992a) discusses the phylogeny of the order, based largely on vegetative features.

Two new genera of Gelidiales have been described recently by Akatsuka: Pterocladiastrum Akatsuka (1986a), based on a new species segregated from the forms of Pterocladia lucida in New Zealand, and Onikusa Akatsuka (1986b), with the type species 0. pristoides (Turner) Akatsuka from South Africa, and O. japonica (Harvey) Akatsuka from Japan. Both these genera are segregated on vegetative features, especially the persistence of surface cells in "tetrads" (essentially in rows) as seen in surface view. This feature however is seen, to a variable extent, in other genera and species and scarcely warrants recognition at generic level (see also Santelices 1990, p. 181); in the case of Pterocladiastrum, separation from Pterocladia lucida is unjustified. Gelidium pristoides (Turner) Kützing and G. japonicum Okamura are probably the most striking species of the genus, with marginal fertile ramuli on flattened fronds, but differ in this respect only in degree from other species of Gelidium (e.g. G. asperum).

The above recent studies of members of the Gelidiales indicate that further generic revisions within the order are likely.

References:

AKATSUKA, I. (1986a). Pterocladiastrum, a new genus segregated from Pterocladia (Gélidiales, Rhodophyta). Bot. Mar. 29, 51–58.

AKATSUKA, I. (1986b). Surface cell morphology and its relationship to other generic characters in non-parasitic Gelidiaceae (Rhodophyta). Bot. Mar. 29, 59–68.

DIXON, P.S. & IRVINE, L.M. (1977b). Seaweeds of the British Isles. Vol. 1, Rhodophyta. Part I, Introduction, Nemaliales, Gigartinales. [British Museum (N.H.): London.]

DIXON, P.S. (1961). On the classification of the Florideae with particular reference to the position of the Gelidiaceae. Bot. Mar. 3, 1–16.

FAN, K.C. (1961). Morphological studies of the Gélidiales. Univ. Calif. Pubis Bot. 32, 315–368.

HOMMERSAND, M.H. & FREDERICQ, S. (1988). An investigation of cystocarp development in Gelidium pteridifolium with a revised description of the Gélidiales (Rhodophyta). Phycologia 27, 254–272.

KYLIN, H. (1923). Studien über die Entwicklungsgeschichte der Florideen. K. Svenska Vetensk. Akad. Handl. 63, 1–139.

MAGGS, C.A. & GUIRY, M.D. (1987). Gelidiella calcicola sp. nov. (Rhodophyta) from the British Isles and northern France. Br. phycol. J. 22, 417–434.

NORRIS, R.E. (1992a). A proposed phylogenetic scheme for the Gélidiales. In Abbott, I.A. (Ed.), Taxonomy of Economic Seaweeds. With reference to some Pacific and Western Atlantic species. Vol. III, pp. 151–171. (Calif. Sea Grant College Program: La Jolla, Calif.)

NORRIS, R.E. (1992b). The marine red algae of Natal, South Africa: Order Gélidiales (Rhodophyta). Mem. Bot. Survey South Africa No. 61.

PUESCHEL, C.M. & COLE, K.M. (1982). Rhodophycean pit plugs: an ultrastructural survey with taxonomic implications. Amer. J. Bot. 69, 703–720.

SANTELICES, B. (1990). New and old problems in the taxonomy of the Gélidiales (Rhodophyta). Hydrobiologia 204/205, 125–135.

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.


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