Electronic Flora of South Australia Family Fact Sheet

FAMILY ELACHISTACEAE Kjellman

Phylum Phaeophyta – Order Chordariales

Thallus epiphytic, pulvinate to tufted, 2–20 mm across and high, consisting of a basal layer of radiating filaments with the cells each producing an erect filament which differentiate to form a medulla of non-pigmented cells bearing an assimilatory cortex of determinate branched filaments together with free, indeterminate, unbranched, assimilatory filaments several times longer than the rest of the thallus; cells with numerous phaeoplasts, each usually with a pyrenoid; phaeophycean hairs absent. Growth of radiating basal layer filaments apical, of cortical filaments apical or subapical, the long assimilatory filaments with a basal meristem. Microthallus filamentous, branched.

Reproduction: Plurilocular sporangia producing zoospores which reform the macrothallus, and unilocular sporangia producing meiospores which form microthalli with plurilocular sporangia or giving rise to macrothalli after diploidisation.

Life history probably direct in most species, often via microthalli, but inadequately known (Pedersen 1981a, p. 203).

Taxonomic notes: A family of three or four genera and about 30 species, most in Elachista. Two genera occur in southern Australia (Skinner 1985), Elachista (including Portphillipia) with three species and Halothrix with one. The Elachistaceae are usually readily recognised by their small tufts of aggregated filaments forming a pulvinate, usually compact, medulla and cortex, surmounted by long, free, assimilatory filaments, and absence of phaeophycean hairs.

References:

PEDERSEN, P.M. (1981a). Phaeophyta: Life histories. In Lobban, C.S. & Wynne, M.J. (Eds), The Biology of Seaweeds, Ch. 5, pp. 194–217. Bot. Monogr. Vol. 17. (Blackwell: Oxford.)

SKINNER, S. (1985). Australian and New Zealand species of Elachista and Halothrix (Elachistaceae, Phaeophyta). Trans. R. Soc. S. Aust. 109, 151–160.

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

KEY TO GENERA OF ELACHISTACEAE

1. Thallus epiphytic on larger algae; plurilocular sporangia filiform, uniseriate, arising from the upper part of medullary filaments or the base of long assimilatory filaments and lying within the cortex; unilocular sporangia borne in a similar position

ELACHISTA

1. Thallus epiphytic on Heterozostera; plurilocular sporangia in sori, intercalary, formed from cells of the long assimilatory filaments; unilocular sporangia, when present, lateral at base of cortical filaments

HALOTHRIX


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