Electronic Flora of South Australia Genus Fact Sheet

Genus HALOTHRIX Reinke 1888: 19

Phylum Phaeophyta – Order Chordariales – Family Elachistaceae

Thallus loosely pulvinate or tufted, to 2 cm high, epiphytic on Zosteraceae, plants single or clustered. Basal layer at first of radiating filaments, soon becoming a dense mass of irregular filaments. Medullary filaments erect from cells of basal layer, several cells long, with branching largely confined to the upper cells. Determinate cortical filaments arising from upper cells of medullary filaments or laterally from base of long assimilatory filaments, unbranched except basally (below their assimilatory part). Long assimilatory filaments extending several times beyond the rest of the thallus, with a basal meristem and short, more or less isodiametric cells.

Reproduction: Plurilocular sporangia formed in sori by subdivision of upper or mid cells of the long assimilatory filaments. Unilocular sporangia arising from upper medullary cells.

Life history direct as far as known.

Type species: H. lumbricalis (Kützing) Reinke.

Taxonomic notes: Halothrix includes some six species, with H. lumbricalis from the North Atlantic, four further species from Japan (Takamatsu 1938, Yoshida et al. 1985, p. 66), and H. ephemeralis the only known species from southern Australia. Pedersen (I 979b) demonstrated a direct life history for H. lumbricalis, and sexuality has not been shown in any species of the genus.

Pedersen (1984, p. 64) has suggested that Halothrix may be better placed in the Giraudiaceae (Dictyosiphonales) on the basis of parenchymatous divisions prior to formation of the plurilocular sporangia, as well as the basal meristem of the long assimilatory filaments and the hypomeristematic branching. However, no parenchymatous divisions occur in vegetative filaments and the genus is retained here in the Elachistaceae.


PEDERSEN, P.M. (1984). Studies on primitive brown algae (Fucophyceae). Opera Bot. 74, 1–76.

REINKE, J. (1888). Die braunen Algen (Fucaceen und Phaeosporeen) der Kieler Bucht. Ber. Deutsch. Bot. Ges. 6, 14–20.

TAKAMATSU, M. (1938). Halothrix aus dem nordöstlichen Honshû, Japan. Saito Ho-on Kai Mus. Res. Bull. 14, 181–192, Plates 24, 25.

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
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