Electronic Flora of South Australia Genus Fact Sheet

Genus ELACHISTA Duby 1830: 972, nom. cons.

Phylum Phaeophyta – Order Chordariales – Family Elachistaceae

Thallus pulvinate, globose, hemispherical or spreading, with long, free, exserted, assimilatory filaments, 2–20 mm high, epiphytic. Basal layer more or less distinct, of radiating filaments, the older cells often with peg-like attachments between the host cells, with each cell from just within the margin producing an erect filament. Erect medullary filaments branched, usually compactly clustered but in some species well separated, of non-pigmented cylindrical to ovoid cells, in some species producing occasional transverse filaments, and surmounted by the cortex of assimilatory filaments and reproductive organs. Determinate cortical filaments of 5–20 cells, usually of uniform height (along with plurilocular sporangia), arising directly from the basal layer or from the lower cells of long assimilatory filaments. Long assimilatory filaments usually numerous, free, simple (from the basal layer or from branches within the cortex), extending several times the length of the rest of the thallus, with a meristem at the level of the cortex, cells densely phaeoplastic.

Reproduction: Plurilocular sporangia filiform, uniserate, with (8–) 15–50 locules, produced from the upper medullary cells or laterally from the lower cells of the long assimilatory filaments. Unilocular sporangia on short pedicels or sessile on upper medullary cells, lying within the cortex.

Life history direct via a filamentous microthallus (in E. fucicola—Kornmann 1962b; Koeman & Cortel-Breeman 1976).

Type species: E. scutulata (Smith) Areschoug.

Taxonomic notes: A genus of at least 20 species, widely distributed in temperate and colder seas, on a variety of hosts. Fifteen species are credited to Japan by Yoshida et al. (1985).

References:

DUBY, J.E. (1830). Botanicon Gallicum seu Synopsis Plantarum in Flora Gallica Descriptarum. Part 2, Plantas Cellulares continens. Edn 2. (Paris.)

KOEMAN, R.P.T. & CORTEL-BREEMAN, A.M. (1976). Observations on the life history of Elachista fucicola (Veil.) Aresch. (Phaeophyceae) in culture. Phycologia 15, 107–117.

KORNMANN, P. (1962b). Plurilokulare Sporangien bei Elachista fucicola. Helgol. wiss. Meeresunters. 8, 293–297.

YOSHIDA, T., NAKAJIMA, Y. & NAKATA, Y. (1985). Preliminary check-list, of marine benthic algae of Japan-I. Chlorophyceae and Phaeophyceae. Jap. J. Phycol. 33, 57–74.

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 SPECIES OF ELACHISTA

1. Long assimilatory filaments unbranched from the basal layer, with separate, subdichotomous filaments bearing the determinate cortical filaments and plurilocular sporangia; unilocular sporangia unknown; epiphytic on Ecklonia

E. orbicularis

1. Medullary filaments all branched, with some upper branches continuing as long assimilatory filaments; plurilocular sporangia borne in lateral branched clusters from the base of long assimilatory filaments, or from medullary branches which bear determinate cortical filaments; unilocular sporangia usually present in a similar position

2

2. Medulla compact, branching from most of the ovoid cells, without transverse filaments; long assimilatory filaments mostly 15–20 µm in diameter; plurilocular sporangia frequent; unilocular sporangia occasional, often present on the same plant

E. claytoniae

2. Medulla of separated, sparsely branched, slender filaments producing below occasional transverse filaments; long assimilatory filaments slender, 8–10 mm in diameter; only unilocular sporangia known

E. australis


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