Electronic Flora of South Australia Genus Fact Sheet

Genus ARESCHOUGIA Harvey 1855a: 554, nom. cons.

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Areschougiaceae

Thallus erect, much branched either irregularly from terete to slightly compressed branches or more or less complanately from the margins of distinctly compressed, often midribbed, branches; holdfast discoid. Structure uniaxial, with the axial cells cutting off a single periaxial cell more or less on three radii, forming a medulla of periaxial filaments and rhizoids (dense in lower parts) and a pseudoparenchymatous cortex of ovoid cells; axial filament conspicuous throughout the thallus.

Reproduction: Sexual thalli monoecious where known; non-procarpic. Carpogonial branches 3 (–4)-celled, borne on inner cortical cells, directed inwards or laterally with reflexed trichogynes, with occasional sterile cells on the basal cell(s); fertilized carpogonium producing 3–7 non-septate connecting filaments. Auxiliary cell an inner cortical cell, with adjacent cortical cells enlarging, staining darker and producing secondary nutritive cells; first gonimoblast initial more or less inwards, becoming radial from a prominent fusion cell (with its stalk) and bearing short chains of carposporangia. Cystocarps with filamentous enveloping tissue, ostiolate. Spermatangia in clusters in nemathecia, between clavate paraphyses, cut off via initial cells from outer cortical cells.

Tetrasporangia scattered in the cortex, basally attached, zonately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Type species: A. laurencia (Hooker & Harvey) Harvey 1855a: 554 [= A. congesta (Turner) J. Agardh]

Taxonomic notes: Areschougia includes three southern Australian species monographed by Min-Thein & Womersley (1976). The genus is most closely related to Rhabdonia, differing in having a conspicuous axial filament throughout the thallus. The type species has been discussed by Silva (1950, p. 267).

References:

HARVEY, W.H. (1855a). Some account of the marine botany of the colony of Western Australia. Trans. R. Ir. Acad. 22, 525–566.

MIN-THEIN, U. & WOMERSLEY, H.B.S. (1976). Studies on southern Australian taxa of Solieriaceae, Rhabdoniaceae and Rhodophyllidaceae (Rhodophyta). Aust. J. Bot. 24, 1–166.

SILVA, P.C. (1950). Generic names of algae proposed for conservation. Hydrobiologia 2, 252–280.

The Marine Benthic Flora of Southern Australia Part IIIA complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 January, 1994)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIA, Bangiophyceae and Florideophyceae (to Gigartinales)
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIA 1994, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

KEY TO SPECIES OF ARESCHOUGIA

1. Branches irregularly radial, essentially terete

A. congesta

1. Branches distinctly compressed, laterals distichous from the margins, essentially complanately branched

2

2. Branches (2–) 2.5–4 mm broad, apices generally obtuse, short laterals only occasionally present on main branches; holdfast with a single axis

A. ligulata

2. Branches 1–2 mm broad, apices generally acute, short laterals usually present on main branches; holdfast with several axes

A. stuartii


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