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Genus ACROSORIUM Zanardini ex Kützing 1869: 4

Phylum Rhodophyta – Family Delesseriaceae

Thallus basally prostrate or decumbent, becoming erect, membranous and delicate, more-or-less complanately branched with alternate to subdichotomous branches a few mm broad, tips rounded and, at least in the type species, often involute and recurved, margins entire to irregularly "ciliate" with clumped rhizoidal projections; slender branched veins present. Attachment by clumped rhizoids. Structure. Blades largely monostromatic, becoming tristromatic and polystromatic only near the base; cells uninucleate or multinucleate.

Reproduction: Gametophytes dioecious. Procarps scattered, with the primary (supporting) cell bearing a first sterile group, a 4-celled carpogonial branch, and a second sterile group.

Type species: A. aglaophylloides Zanardini ex Kützing 1869: 4, pl. 10a, b. [= A. uncinatum sensu Kylin 1924: 78, fig. 61, = A. venulosum (Zanardini) Kylin 1924: 77, fig. 60 = A. ciliolatum (Harvey) Kylin 1924: 78].

Taxonomic notes: Carposporophyte with a basal fusion cell and a much branched gonimoblast with terminal carposporangia, maturing in succession. Cystocarps ostiolate, with or without a collar, pericarp 3–6 cells thick. Spermatangial sori near branch tips.

Tetrasporangial sori usually single and relatively large near tips of branches, with tetrasporangia in 2 layers, of mixed ages, cut off from primary and/or inner cortical cells and covered by outer cortical cells.

A genus of several recorded species, most of which need careful comparison with the type. The above description of cystocarpic stages is based mainly on Australian material of the type species (see below) and on Papenfuss (1939) who described the South African A. acrospermum.

Acrosorium ciliolatum is probably the only species on southern Australian coasts. Acrosorium minor (Sonder) Kylin (1924, p. 78) from the vicinity of Fremantle, W. Aust., is little known and may not be an Acrosorium (see below under "Species of uncertain status"). Kylin (1929, pp. 11, 14) considered it to be close to A. decumbens (J. Agardh) Kylin from New Zealand. Specimens in TCD under A. minus include 2 species; Harvey's 296a and Clifton from Fremantle are mostly tristromatic and may be a small Hymenena, while one of Clifton from "W. Aust." is probably a Rhodophyllis.


KÜTZING, F.T. (1869). Tabulae Phycologicae. Vol. 19. (Nordhausen.)

KYLIN, H. (1924). Studien über die Delesseriaceen. Lunds Univ. Årsskr. N.F. Avd. 2, 20(6), 1–111.

KYLIN, H. (1929). Die Delesseriaceen Neu-seelands. Lunds Univ. Årsskr. N.F. Avd. 2, 25(2), 1–15, Plates 1–12.

PAPENFUSS, G.F. (1939). The development of the reproductive organs in Acrosorium acrospermum. Bot. Notiser 1939, 11–20.

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

Author: H. B. S. Womersley

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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