Electronic Flora of South Australia Genus Fact Sheet

Genus DICRANEMA Sonder 1845: 56

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Dicranemataceae

Thallus subdichotomously branched, cartilaginous, branches filiform, divaricate, apices truncate to rounded, obligately epiphytic on the sea-grass Amphibolis. Structure multiaxial, with a medullary core of narrow, elongate cells and a broad pseudoparenchymatous cortex of larger, ovoid, inner cells and smaller outer cells.

Reproduction: Sexual thalli monoecious; non-procarpic. Carpogonial branches 2-celled, straight, borne around branch apices on inner cortical (supporting) cells, with adjacent cortical cells acting as auxiliary cells; fusion cell forming a reticulum with adjacent cortical cells, with an inwardly directed inner placental layer of gonimoblast and gametophyte cells, developing a cavity by autolysis of peripheral gametophyte cells into which gonimoblast filaments ramify, producing terminal obovoid carposporangia. Cystocarps swelling the branch, with an ostiole present or absent, differentiating from the inner cortex outwards. Spermatangia in sunken, isolated, clusters near branch tips, catenate.

Tetrasporangia in nemathecia surrounding upper branches, basally attached, zonately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Lectotype species: D. grevillei Sonder 1845: 56 [= D. revolutum (C. Agardh) J. Agardh].

Taxonomic notes: A genus with two southern Australian species (Kraft 1977b), other species having been excluded from the genus by Kraft (1977b, p. 233). D. rosaliae Setchell & Gardner from Baja California, Mexico, with unknown reproduction, is more likely to be a species of Gelidiopsis or Wurdemannia.

References:

KRAFT, G.T. (1977b). Studies of marine algae in the lesser-known families of the Gigartinales (Rhodophyta). H. The Dicranemaceae. Aust. J. Bot. 25, 219–267.

SONDER, O.G. (1845). Nova Algarum genera et species, quas in itinere ad oras occidentales Novae Hollandiae, collegit L. Preiss, Ph.Dr. Bot. Zeit. 3, 49–57.

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

Author: G. T. Kraft & 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 DICRANEMA

1. Thallus 2–5 (–7) cm high, openly branched, lower branches erect and straight, only the upper branches curved or recurved

D. revolutum

1. Thallus 3–5 mm high, densely branched, all of the branches strongly curled

D. cincinnalis


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