Electronic Flora of South Australia Genus Fact Sheet

Genus ACROSYMPHYTON Sjöstedt 1926: 8

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Dumontiaceae

Thallus (gametophytes) erect, much branched, branches terete, usually mucilaginous. Structure uniaxial, with whorls of four periaxial cells per axial cell and laterals of several orders, the inner ones forming a loose medulla with descending rhizoids and the outer cells forming a lax to coherent cortex. Rhodoplasts numerous per cell, discoid to elongate.

Tetrasporophytes (known only in A. purpuriferum) prostrate, of branched filaments [Cortel-Breeman & van den Hoek (1970)1.

Reproduction: Sexual plants monoecious or dioecious. Carpogonial and auxiliary cell branches scattered in younger branches, borne on periaxial or inner medullary cells. Carpogonial branches several cells long, with mid cells bearing lateral branches 1–4 cells long, with post-fertilization fusions to these cells prior to formation of connecting filaments. Auxiliary cell branches 5–16 cells long, auxiliary cell terminal. Carposporophytes compact, with all cells becoming carposporangia. Spermatangia clustered on outer cortical cells.

Life history triphasic with heteromorphic gametophytes and tetrasporophytes.

Lectotype species: A. purpuriferum (J. Agardh) Sjöstedt 1926: 9.

Taxonomic notes: Tetrasporophyte (where known) producing tetrahedrally divided tetrasporangia, or "seriate tetrasporangia" which re-cycle the tetrasporophyte.

A genus of 5 species, the type from the Mediterranean, A. caribaeum (J. Agardh) Sjöstedt from Bermuda and Florida, A. taylorii Abbott from the Hawaiian Islands and Australia, A. firmum Hawkes from New Zealand, and A. tenax Millar & Kraft (1984, p. 140, figs 11–26) from northern N.S.W.

Acrosymphyton is distinguished by post-fertilization connection of the carpogonium to cells of the laterals on the carpogonial branch, from which connecting filaments issue, by the auxiliary cells being terminal, and by heteromorphic gametophytes and tetrasporophytes (where known). Lindstrom (1987) has erected the family Acrosymphytaceae on the basis of pinnately branched carpogonial branches, with filaments from the fertilized carpogonium contacting terminal cells of the laterals, terminal auxiliary cells, and other reproductive features. Some of these features differ only in degree from the Dumontiaceae, e.g. sterile laterals occur on the carpogonial branches in Dudresnaya and Kraftia, and auxiliary cells may be terminal to fourth in Neodilsea natashae (Lindstrom 1984, p. 34). For the present, Acrosymphyton is kept within the Dumontiaceae.

References:

LINDSTROM, S.C. (1984). Neodilsea natashae sp. nov. (Dumontiaceae, Rhodophyta) with comments on the family. Phycologia 23, 29–37.

LINDSTROM, S.C. (1987). Acrosymphytaceae, a new family in the order Gigartinales sensu lato (Rhodophyta). Taxon 36, 50–53.

MILLAR, A.J.K. & KRAFT, G.T. (1984). The red algal genus Acrosymphyton (Dumontiaceae, Cryptonemiales) in Australia. Phycologia 23, 135–145.

SJÖSTEDT, L.G. (1926). Floridean studies. Lunds Univ. Årsskr. N.F. Avd. 2, 22 (4), 1–95.

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.


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