Electronic Flora of South Australia Family Fact Sheet


Phylum Phaeophyta – Order Dictyosiphonales

Thallus forming dense to loose, more or less hemispherical, tufts, usually less than I cm high, epiphytic on the seagrass Posidonia or on algae. Basal plate monostromatic, discoid, of radiating filaments, developing erect medullary filaments, then with erect, polystichous axes. Axes simple or occasionally branched, uniseriate below, becoming multiseriate above and forming tiers, each of 2–16 cells, with numerous phaeoplasts each with a pyrenoid. Phaeophycean hairs terminal and often lateral.

Microthalli myrionemoid, with ascocysts.

Reproduction: Reproduction by plurilocular sporangia borne on basal or erect filaments, in lateral sori on erect axes, or as intercalary sori by subdivision of cells of erect axes; unilocular sporangia (in Giraudia robusta only) borne on upper cells of medullary filaments. Microthalli reproducing by uni-, bi- or multiseriate plurilocular sporangia.

Life history probably largely direct.

Taxonomic notes: A family of two genera, with the type species of Giraudia fairly widely distributed, the other taxa known only from southern Australia.

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


1. Basal plate producing erect medullary cells then erect axes broadest above their uniseriate, meristematic, base, developing 5–16 cells per tier, then tapering to their apices with 1-several hairs; plurilocular sporangia basal, lateral or intercalary


1. Basal plate monostromatic, producing directly erect, filiform axes with 2–3 cells per tier, with a single terminal hair; plurilocular sporangia terminal or intercalary


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