Electronic Flora of South Australia Genus Fact Sheet
Phylum Phaeophyta – Order Chordariales – Family Ralfsiaceae
Thallus a few mm to several cm across and usually less than 1 (–3) mm thick, crustose but gelatinous, firmly adherent to the substratum and usually without rhizoids. Basal layer of radiating filaments two (–4) cells thick. Erect filaments radially assurgent but usually soon becoming erect, simple or occasionally branched, readily separating under slight pressure. Phaeophycean hairs present singly or in clusters, or absent. Phaeoplasts laminate, one to a few per cell, without pyrenoids.
Reproduction: Unilocular sporangia borne terminally on the erect filaments or on laterals from lower parts of vegetative filaments and often positioned within the thallus. Plurilocular sporangia arising in an intercalary position in erect filaments, with one or a few terminal sterile cells (often lost), and becoming pluriseriate over few to many cells.
Life history uncertain, possibly diplohaplontic and isomorphic.
Type species: H. gelatinosum Saunders 1899.
Taxonomic notes: Two other genera, Mesospora Weber van Bosse (1910) and Basispora John & Lawson (1974) are closely related to Hapalospongidion and should be relegated to synonymy. The type of Mesospora, M. schmidtii W. van Bosse, is described in detail by Tanaka & Chihara (1982), who considered that this genus differs from Hapalospongidion in having a single laminate phaeoplast per cell and unilocular sporangia borne terminally on a several-celled stalk which arises from the basal cell of a vegetative filament. However, Tanaka & Chihara (p. 383) refer to "chloroplasts ... in upper cells ... one per cell ... in lower part of thallus, two to three in each cell", and Abbott & Hollenberg (1976, p. 171) refer to Hapalospongidion having "mostly one chloroplast per cell". It appears that both Mesospora and Hapalospongidion have one to three phaeoplasts per cell, probably dependent on size and age of the cells. Likewise there seems to be little difference between these two genera in position of the unilocular sporangia, which are terminal on vegetative filaments which may or may not have branched close to their base.
Basispora John & Lawson (1974) was based on B. africana John & Lawson from West Africa as type species, and two New Zealand taxa were transferred to it, viz. Hapalospongidion saxigenum Lindauer and H. durvilleae Lindauer. The latter has been made the type of a new genus, Herpodiscus, by South (1974) and referred tentatively to the Elachistaceae of the Chordariales; it is certainly unrelated to the Ralfsiaceae. Basispora was distinguished by "the terminal unilocular sporangia arising on long stalks from near the base of the simple, often assurgent, laterally free erect filaments". These features are shown by Hapalospongidion (Hollenberg 1942, fig. 1), and Basispora also has several phaeoplasts per cell.
In the southern Australian taxon described below, the number of phaeoplasts per cell is not clear, but in some smaller cells only one is apparent while larger cells probably have 2–3. It appears that neither the number of phaeoplasts per cell nor the position of the unilocular sporangium permits recognition of more than one genus in this group, and the erect filaments in all taxa probably arise in an assurgent manner, though this is only slight in the southern Australian species.
ABBOTT, I.A. & HOLLENBERG, G.J. (1976). Marine Algae of California. (Stanford Univ. Press: Stanford.)
HOLLENBERG, G.J. (1942). Phycological Notes. I. Bull. Torrey Bot. Club 69, 528–538.
JOHN, D.M. & LAWSON, G.W. (1974). Basispora, a new genus of the Ralfsiaceae. Br. ph y-col. J. 9, 285–290.
SAUNDERS, DE A. (1899). New and little known brown algae of the Pacific Coast. Erythrea 7, 37–40.
SOUTH, G.R. (1974). Herpodiscus gen. nov. and Herpodiscus durvilleae (Lindauer) comb. nov., a parasite of Durvillea antarctica (Chamisso) Hariot endemic to New Zealand. J. R. Soc. N.Z. 4, 455–461.
TANAKA, J. & CHIHARA, M. (1982). Morphology and taxonomy of Mesospora schmidtii Weber van Bosse, Mesosporaceae fam. nov. (Ralfsiales, Phaeophyceae). Phycologia 21, 382–389.
WEBER VAN BOSSE, A. (1910). Notice sur quelques genres nouveaux d'algues de l'Archipel Malaisien. Ann. Jard. Bot. Buitenzorg. Sér. 2, 9, 25–33.
The Marine Benthic Flora of Southern Australia Part II complete list of references.
Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
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