Electronic Flora of South Australia Genus Fact Sheet

Genus PHLOIOCAULON Geyler 1866: 509, 529

Phylum Phaeophyta – Order Sphacelariales – Family Stypocaulaceae

Thallus 5–30 cm long, forming erect, spreading plants or loose tufts with one to several long axes and laterals, epilithic, attached by a basal disc, axes smooth and without loose, descending rhizoids. Axes and larger branches prominent, with an extensive secondary cortex developed from appressed rhizoidal filaments covering the primary cortex, with the cells of the appressed filaments producing radial filaments forming a pseudoparenchymatous inner secondary cortex (of which the cells enlarge with age) and on older axes a smaller-celled outer secondary cortex; phaeophycean hairs present in axils of laterals. Growth acroblastic and auxocaulic (in that the inner primary cells increase in length and the inner secondary cortical cells increase in size).

Reproduction: Reproduction by unilocular sporangia borne in axils of laterals, accompanied by two subtending bracts, or also on the axes; sexual plants with plurilocular macro- and microgametangia, with large or small loculi, borne in small groups in similar positions to the sporangia.

Life history diplohaplontic and isomorphic; sexual reproduction anisogamous.

Type species: P. squamulosum (Suhr) Geyler.

Taxonomic notes: A genus of three species, the type from South Africa and two from southern Australia.

Phloiocaulon is a distinctive genus on southern Australian coasts, differing from Halopteris in having prominent axes with smooth-surfaced, secondary cortication. H. platycena lacks corticating rhizoids but does not have the secondary cortication of Phloiocaulon. The plurilocular


gametangia, with locules of two sizes, indicate that Phloiocaulon is probably anisogamous, in contrast to the oogamy of Halopteris.

In Phloiocaulon, the reproductive organs are borne on short pedicels in the axils of laterals or on their axes, in contrast to Ptilopogon* where they are borne on branched, axillary, systems.


GEYLER, T. (1866). Zur Kenntnis der Sphacelariaceen. Jb. wiss. Bot. 4, 479–535, Plates 34–36.

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
©Board of the Botanic Gardens and State Herbarium, Government of South Australia


1. Sporangia and gametangia visible in surface view in axils of laterals which form loose spikes, with 1–2 (–3) sporangia and 2–5 gametangia in each axil and subtended by two, simple or branched, bracts; sporangia (50–) 70–90 (–105) µm in diameter

L P. spectabile

1. Sporangia and gametangia hidden from surface view, in dense spikes, occurring both in the axils of laterals and on their axes; sporangia 100–160 (–180) µm in diameter

P. foecundum

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