Electronic Flora of South Australia Family Fact Sheet

FAMILY STYPOCAULACEAE Oltmanns

Phylum Phaeophyta – Order Sphacelariales

Reproduction: Reproduction by unilocular meiosporangia; sexual plants anisogamous or oogamous, with gametangia borne on the same plant.

Taxonomic notes: Mathis 3–15 (–30) cm long, forming dense tufts, usually epilithic, attached by basal rhizoidal discs or a loose holdfast of descending rhizoidal filaments. Erect filaments much branched, with indeterminate or determinate laterals; internal structure of larger medullary cells covered by a small-celled cortex formed close to the apical cells and which remains monostromatic except in H. paniculata; many species with further cortication by descending rhizoids; phaeophycean hairs in axillary clusters or absent. Growth apical, with branches and hairs acroblastic or axillary; secondary growth of segments absent or present. Cells with many small, discoid phaeoplasts and physodes.

This family includes four genera, Halopteris Kützing (including Stypocaulon Kützing), Phloiocaulon Reinke, Alethocladus Sauvageau from Kerguelen I., and the New Zealand Ptilopogon Reinke. They differ from the Sphacelariaceae in being larger, corticated plants with acroblastic branching, and in having anisogamous or (in most species) oogamous reproduction, though sexual plants are usually rare compared to asexual ones. It appears likely that meiosis does not always occur in unilocular sporangia and this generation is then repeated. The family Cladostephaceae differs in having whorled laterals, the axes show secondary growth and hypacroblastic branching, and the whorled laterals are determinate and branch acroblastically.

The Stypocaulaceae is a widespread family in temperate waters, with some 11 species of Halopteris, the greatest number of taxa being on southern Australian coasts. The other genera have only 1–3 species each.

References: The Marine Benthic Flora of Southern Australia Part II

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

KEY TO GENERA OF STYPOCAULACEAE

1. Lower axes with no or slight secondary cortex, in most species further corticated with few to many descending rhizoidal filaments; sexual reproduction oogamous

HALOPTERIS

1. Lower axes with thick secondary cortex, smooth, without corticating rhizoidal filaments; sexual reproduction anisogamous

PHLOIOCAULON


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