Electronic Flora of South Australia Genus Fact Sheet
Phylum Phaeophyta – Order Chordariales – Family Leathesiaceae
Thallus 5–40 mm across, crustose to low-pulvinate with broad radiating lobes, surface smooth to slightly rugose, growing radially at the margins and older central parts dying. Basal layer of entwined rhizoidal filaments of short cells. Medulla extensive, of erect, closely associated, branched filaments producing rhizoids laterally and cortical filaments and hairs from the upper cells. Determinate cortical filaments arising from upper medullary cells, forming a dense stratum of even height, 4–10 cells long, branched 1–3 times, cylindrical and without inflated terminal cells. Phaeoplasts several per cell, discoid, each with a pyrenoid.
Reproduction: Plurilocular sporangia terminal on determinate cortical filaments, multiseriate (in P. berkeleyi), unknown in P. rugosum. Unilocular sporangia basally or laterally attached, sessile or pedicellate, borne from lower cells of determinate cortical filaments, irregularly elongate-ovoid.
Life history with macroscopic sporophyte and gametophytic microthallus producing isogametes (Arasaki 1948).
Type species: P. berkeleyi (Greville) Naegeli.
Taxonomic notes: Petrospongium contains two species, the type from the North Atlantic and Mediterranean, and P. rugosum from the Pacific, including southern Australia.
Cylindrocarpus Crouan & Crouan is often considered (e.g. Parke et al. 1976, Abbott & Hollenberg 1976) to include Petrospongium, but was kept separate by Setchell & Gardner (1925, p. 509). The type species of Cylindrocarpus, C. microscopicus Crouan & Crouan, is a minute alga with separate erect filaments arising from an endophytic base and without a well-developed medulla. It is as distinct in morphology from the two species of Petrospongium as the distinctions between other genera of the Leathesiaceae.
ABBOTT, I.A. & HOLLENBERG, G.J. (1976). Marine Algae of California. (Stanford Univ. Press: Stanford.)
ARASAKI, S. (1948). On the life-history of the Acrothrix pacifica, Myriocladia kuromo and Petrospongium rugosum. Seibutu 3, 95–102.
KÜTZING, F.T. (1858). Tabulae Phycologicae. Vol. 8. (Nordhausen.)
PARKE, M., DIXON, P.S., RUSSELL, G. & FLETCHER, R.L. (1976). In Parke, M. & Dixon, P.S. Check-list of British marine algae-third revision. J. mar. biol. Ass. U.K. 56, 527–594.
SETCHELL, W.A. & GARDNER, N.L. (1925). The marine algae of the Pacific coast of North America. Part III. Melanophyceae. Univ. Calif Publ. Bot. 8, 383–898, Plates 34–107.
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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State Herbarium of South Australia