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Electronic Flora of South Australia Genus Fact Sheet

Genus PETALONIA Derbés & Solier 1850: 265, nom. cons.

Phylum Phaeophyta – Order Scytosiphonales – Family Scytosiphonaceae

Thallus erect 5–20 (–40) cm high, lanceolate to cuneate, simple, with a small holdfast and stipe, broadening rapidly or gradually above the base. Structure polystichous, with a medulla of irregular, clear cells 2–4 (–8) cells thick, and a 1–2 cell thick cortex of distinctly smaller cells, each with a single phaeoplast and pyrenoid, and with phaeophycean hairs rare to occasional in small groups. Alternate stage crustose, haplostichous, with a prostrate hypothallium of radiating filaments bearing short, erect filaments.

Reproduction: Reproduction by plurilocular organs in extensive surface sori without paraphyses, producing zooids which reproduce the erect thallus or the alternate crustose stage with unilocular sporangia producing mitospores (Wynne 1969, p. 17, figs 6–8; Nakamura & Tatewaki 1975, p. 72, figs 11–14).

Life history probably direct, apparently non sexual.

Type species: P. debilis (C. Agardh) Derbés & Solier [= P. fascia (Müller) Kuntze].

Taxonomic notes: A genus of 2–3 species, with the type species widely distributed in temperate waters. Several authors (e.g. Wynne 1969, p. 17; Edelstein et al. 1970) have shown that the crustose stage corresponds with Ralfsia (Stragularia) clavata (Harvey) Crouan & Crouan, and Roeleveld et al. (1974) have described the seasonal cycle of P. fascia in the Netherlands, where the crustose stage occurs only in summer. Sexual reproduction has not been observed in Petalonia.

Petalonia differs from Scytosiphon in having a solid thallus, in phaeophycean hairs being much less plentiful or even absent, and in the absence of unicellular paraphyses in the sori of plurilocular reproductive organs (Wynne 1969, p. 18). The previous records (Womersley 1967, p. 245) of Petalonia zosterifolia (Reinke) Hamel are now referred to the compressed form of Scytosiphon lomentaria (see below), though further studies are clearly needed to clarify the differences between slender, compressed forms of these two species (see Rosenvinge & Lund 1947, p. 37).


DERBÉS, A. & SOLIER, A.J.J. (1850). Sur les organes reproducteurs des Algues. Ann. Sci. nat. (Bot.), Ser. 3, 14, 261–282, Plates 32–37.

EDELSTEIN, T., CHEN, L. C-M. & McLACHLAN, J. (1970). The life cycle of Raffsia clavata and R. borneti. Can. J. Bot. 48, 527–531, Plates I–III.

NAKAMURA, Y. & TATEWAKI, M. (1975). The life history of some species of the Scytosiphonales. Sci. Pap. Inst. Algol. Res. Hokkaido Univ. 6, 57–93, Plates 1–5.

ROELEVELD, J.G., DUISTEROF, M. & VROMAN, M. (1974). On the year cycle of Petalonia fascia in the Netherlands. Netherlands J. Sea Res. 8, 410–426.

ROSENVINGE, L.K. & LUND, S. (1947). The marine algae of Denmark. Vol. II. Phaeophyceae. III. Encoeliaceae, Myriotrichiaceae, Giraudiaceae, Striariaceae, Dictyosiphonaceae, Chordaceae and Laminariaceae. K. Dan. Vidensk. Selsk. Biol. Skr. 4(5), 1–99.

WOMERSLEY, H.B.S. (1967). A critical survey of the marine algae of southern Australia. II. Phaeophyta. Aust. J. Bot. 15, 189–270.

WYNNE, M.J. (1969). Life history and systematic studies of some Pacific North American Phaeophyceae (brown algae). Univ. Calif Publ. Bot. 50, 1–88.

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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