Electronic Flora of South Australia Genus Fact Sheet

Genus RALFSIA Berkeley in Smith & Sowerby 1843: pl. 2866

Phylum Phaeophyta – Order Chordariales – Family Ralfsiaceae

Thallus crustose, round to irregularly spreading, up to 2 mm thick and several cm across, strongly adherent to the rock or other solid substrate, without rhizoids in most species. Basal layer of one to several layers of radiating filaments producing assurgent filaments with the margin of the thallus a few to several filaments thick. Erect filaments continuing from assurgent filaments, adhering laterally under pressure. Cells with a single, laminate phaeoplast usually in their upper end. Phaeophycean hairs present, usually clustered in pits and arising from the lower layers of the thallus.

Reproduction: Reproduction by plurilocular sporangia formed in sori on the upper surface, consisting of uniseriate or biseriate rows of locules, each row with one (–3) sterile terminal cell. Unilocular sporangia borne on the erect filaments and subtended by a uniseriate, usually slightly clavate paraphysis from the same filament, occurring in sori on the upper surface of the thallus.

Life history diplohaplontic with isomorphic generations, but probably more usually direct from plurilocular sporangia or apomeiotic unilocular sporangia.

Type species: R. deusta (C.Agardh) J.Agardh (NON R. deusta Berkeley) [-R. fungiformis (Gunnerus) Setchell & Gardner].

Taxonomic notes: Ralfsia has been credited with two subgenera, (Eu)ralfsia Batters with radially assurgent filaments and Stragularia Stroemfelt with erect filaments from a 1–3 cell thick basal layer. Most of the species of Stragularia are now known to be the sporophytic phase of Scytosiphonales and subgenus Ralfsia is characterised by a compact thallus with radially assurgent filaments, bearing either unilocular sporangia with a paraphysis or plurilocular sporangia in vertical rows with a sterile terminal cell(s).

No species of Ralfsia has been recorded previously on southern Australian coasts, though the genus has been known to be present. The following species is common in the mid eulittoral, and a detailed survey may show that other species occur.

References:

SMITH, J.E. & SOWERBY, J. (1843). English Botany. Suppl. 3, Plate 2866. (London.)

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
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