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Electronic Flora of South Australia Family Fact Sheet
Phylum Phaeophyta – Order Chordariales
Reproduction: The sporophyte by unilocular meiosporangia (often apomeiotic) and the gametophyte by plurilocular organs with neutral spores (or anisogametes in Nemoderma). Reproductive organs intercalary, lateral or terminal on the erect filaments.
The Ralfsiaceae have been elevated to an order with 4 families (Nakamura 1972; Tanaka & Chihara 1982) and some 19 genera, and three genera can now be recorded from southern Australia. The status of this group is uncertain, and some authors (e.g. Bold & Wynne 1985, p.314; Wynne 1981, p. 69; 1982, p. 116) prefer to refer the family to the Ectocarpales. Nakamura characterised his order Ralfsiales as having an isomorphic life history, cells with a single phaeoplast without a pyrenoid, and a discoid germination stage. However, a life history involving sexuality has been established only in the genus Nemoderma (Kuckuck 1912) and many taxa show only direct life histories (Loiseaux 1968), other genera than Ralfsia may have several phaeoplasts per cell (Hollenberg 1969 for Californian taxa; Fletcher 1978 for British taxa; Tanaka & Chihara 1980a,b, 1981, 1982 for Japanese taxa), and the discoid germination stage does not always occur (Fletcher 1978). These features are reviewed by Nelson (1982), who considers that an order is not justified. It has also been suggested that the erect filaments are characteristically assurgent in radial section of the thallus, in contrast to the sporophytic crusts of Scytosiphon and its allies (some of which have been included in the subgenus Stragularia of Ralfsia), but erect filaments occur in several genera placed in the Ralfsiales (Hollenberg 1969, Fletcher 1978). Clearly more detailed life history studies of members of the Ralfsiaceae are needed to establish the relationships of this family, and which members are only stages of taxa in the Scytosiphonales. The family Ralfsiaceae is recognised here for crustose epilithic browns which are seemingly distinct entities, in contrast to sporophytic crusts of Scytosiphonales.
The Ralfsiaceae are included here as a family of the Chordariales because of their close structural similarity to the Myrionematacae and lack of recent evidence that members show an isomorphic diplohaplontic life history.
Crustose brown algae are not uncommon in the intertidal and subtidal zones on southern Australian coasts, but have been little investigated. Clayton (1976a,b, 1981b) has studied the crusts of Scytosiphon (see later), but no named species of Ralfsiaceae have been recorded. As well as the 3 taxa described below, one collection may be referable to Diplura [Lorne, Vic., low eulittoral pools ( Womersley, 23.i.1967; ADU, A31541)] and a second species of Ralfsia may be present [Cape Northumberland, S. Aust., 2–3 m deep on Archaeolithothamnion (Edyvane, 5.vi.1982; ADU, A55513)]. The following account of the ralfsioid algae is therefore provisional.
Life history supposedly diplohaplontic and isomorphic, but probably more usually direct from the sporophyte (Loiseaux 1968).
Taxonomic notes: Thallus a prostrate, rounded to irregularly spreading crust, surface smooth to convolute, developing usually from a discoid germination stage. Basal layer of radiating appressed filaments, usually without rhizoids, becoming 2–4 cells thick with each cell producing a simple or slightly branched, erect or assurgent, filament. Growth from terminal cells of prostrate and erect filaments, occasionally with divisions of subapical cells. Phaeoplasts single or few per cell, plate-like, usually without a pyrenoid.
References:
BOLD, H.C. & WYNNE, M.J. (1985). Introduction to the Algae: Structure and reproduction. 2nd Edn. (Prentice-Hall: New Jersey.)
CLAYTON, M.N. (1976a). The morphology, anatomy and life history of a complanate form of Scytosiphon lomentaria (Scytosiphonales, Phaeophyta) from southern Australia. Mar. Biol. (Berl.) 38, 201–208.
CLAYTON, M.N. (1981b). Experimental analysis of the life history of the complanate form of Scytosiphon (Scytosiphonaceae, Phaeophyta) in southern Australia. Phycologia 20, 358–364.
FLETCHER, R.L. (1978). Studies on the family Ralfsiaceae (Phaeophyta) around the British Isles. In Irvine, D.E.G. & Price, J.H. (Eds), Modern approaches to the taxonomy of red and brown algae. Systematics Association Special Volume 10, 371–388. (Academic Press: London.)
HOLLENBERG, G.J. (1969). An account of the Ralfsiaceae (Phaeophyta) of California. J. Phycol. 5, 290–301.
KUCKUCK, P. (1912). Neue Untersuchungen Ober Nemoderma Schousboe. Wiss. Meeresunters. Abt. Helgol., N.F. 5, 117–152, Plates 4–6.
LOISEAUX, S. (1968). Recherches sur les cycles de dêveloppement des Myrionématacées (Phéophycées). III. Tribu des Ralfsiées. IV. Conclusions générales. Rev. Gén. Bot. 75, 295–318.
NAKAMURA, Y. (1972). A proposal on the classification of the Phaeophyta. In Abbott, I.A. & Kurogi, M. (Eds), Contributions to the systematics of benthic marine algae of the North Pacific, pp. 147–156. (Jap. Soc. Phycol: Kobe.)
NELSON, W.A. (1982). A critical review of the Ralfsialcs, Ralfsiaceae and the taxonomic position of Analipus japonicus (Harv.) Wynne (Phaeophyta). Br. phrcol. J. 17, 311–320.
TANAKA, J. & CHIHARA, M. (1980a). Taxonomic study of the Japanese crustose brown algae (1). General account and the order Ralfsiales. J. Jap. Bot. 55, 193–201.
TANAKA, J. & CHIHARA, M. (1982). Morphology and taxonomy of Mesospora schmidtii Weber van Bosse, Mesosporaceae fam. nov. (Ralfsiales, Phaeophyceae). Phycologia 21, 382–389.
WYNNE, M.J. (1981). Phaeophyta: Morphology and classification. In Lobban, C.S. & Wynne, M.J. (Eds), The Biology of Seaweeds, Ch. 2, pp. 52–85. Bot. Monogr. Vol. 17. (Blackwell: Oxford.)
The Marine Benthic Flora of Southern Australia Part II complete list of references.
Publication:
Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia
KEY TO GENERA OF RALFSIACEAE
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1. Thallus with a basal layer one-several cells thick, producing radially assurgent filaments which become erect and firmly adherent laterally; margin of crusts several filaments thick; unilocular sporangia each accompanied by a paraphysis; plurilocular sporangia uniseriate (occasionally biseriate) with a sterile terminal cell, formed in sori; cells with a single phaeoplast | RALFSIA |
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1. Thallus with a basal layer up to 3 cells thick, the upper cells producing erect filaments (or only slightly assurgent initially) which usually separate readily; margin of crusts monostromatic, unilocular sporangia terminal and without a paraphysis; plurilocular sporangia uniseriate or becoming multiseriate | 2 |
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2. Thallus with cylindrical erect filaments of short cells (L/B | PSEUDOLITHODERMA |
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2. Thallus with long erect filaments, broader above with enlarged apical and subapical cells, lower cells L/B | HAPALOSPONGIDION N.B. Sporophytic crusts of Scytosiphonales correspond in part with the second dichotomy of 1. |
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