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Genus HETEROSTROMA Kraft & Wynne 1992: 17.

Phylum Rhodophyta – Family Rhodomelaceae – Tribe Pterosiphonieae

Thallus with prostrate blades bearing assurgent fronds alternately pinnate 3–4 times, complanately branched, branches flat, ecorticate, margins regularly serrate with pointed determinate laterals, each with a protruding apical cell, some becoming indeterminate.

Attachment by clumped rhizoids. Structure. Subapical axial cells cutting off 4 pericentral cells, 2 on each surface, the dorsal pericentral cells dividing transversely and longitudinally to form short cells covering the larger ventral pericentral cells which divide only longitudinally. Axial cells usually branching alternately every 2 cells and also producing unicellular primordia from alternate cells on alternate sides. Trichoblasts only associated with reproductive structures, Rhizoids unicellular, cut off from pericentral cells, haptera multicellular.

Reproduction: All reproductive organs borne on short marginal processes with 5 pericentral cells. Gametophytes dioecious. Procarps on suprabasal cell of trichoblasts, with a 4-celled carpogonial branch and 2 sterile groups; cystocarps ovoid, ostiolate. Spermatangial organs borne as a basal branch of trichoblasts, elongate-ovoid, axial cells with 3 pericentral cells bearing initials and a surface layer of spermatangia.

Tetrasporangial stichidia marginal, bearing trichoblasts, tetrasporangia spirally arranged, one per segment of 5 pericentral cells, with 3 cover cells.

Type (and only) species: H. nereidiis Kraft & Wynne 1992: 18, figs 2–36.

Taxonomic notes: Heterostroma was described in detail by Kraft & Wynne, who compared it with other flat, congenitally united, blade-like Rhodomelaceae, concluding that it has no close relatives but vegetatively is most similar to Aphanocladia and Jeannerettia. The latter genus is shown below to be correctly named Pollexfenia. Heterostroma is closest to Pollexfenia in thallus construction and reproduction and is provisionally placed in the Pterosiphonieae. It differs from Pollexfenia mainly in having only the pericentral cells on the dorsal surface dividing transversely (on both sides in Pollexfenia), and in the alternately spinous margins.


KRAFT, G.T. & WYNNE, M.J. (1992). Heterostroma nereidiis gen. et. sp. nov. (Rhodophyta), a dorsiventral rhodomelaceous marine alga from Western Australia. Phycologia 31, 16–36.

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

Publication: Womersley, H.B.S. (24 February, 2003)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIID. Ceramiales – Delesseriaceae, Sarcomeniaceae, Rhodomelaceae
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIID 2003, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

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