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Electronic Flora of South Australia Genus Fact Sheet

Genus HETEROTHAMNION J. Agardh 1892: 25

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Heterothamnieae

Thallus with erect axes in dense tufts attached to the host by penetrating rhizoids; epiphytic on Cystophora spp. or Platythalia. Each axial cell with (2–) 4 whorl-branchlets (with basal cells slightly longer than next outer cells) which are simple or only slightly branched from basal or upper cells, decreasing in length, branching and number of whorl-branchlets towards the base of the thallus; gland cells on the third to fifth cells of rachides of whorl-branchlets, cut off from terminal or lower cells, touching the bearing cell and sometimes the next cell. Lateral branches develop from the basal cells of whorl-branchlets. Cells uninucleate.

Reproduction: Gametophytes dioecious. Procarps on the second or third axial cells below apices, consisting of a supporting cell with a sterile cell and a 4-celled carpogonial branch (possibly derived from a 2-celled whorl-branchlet). Carposporophytes with several rounded gonimolobes loosely surrounded by whorl-branchlets from below, each lobe with a basal elongate sterile cell. Spermatangia terminal on branched clusters of cells on the whorl-branchlets.

Tetrasporangia produced on the upper side of whorl-branchlet cells, with or without a basal pedicel, tetrahedrally divided.

Type species: H. muelleri (Sonder) J. Agardh 1892: 25.

Taxonomic notes: A genus of 4 species, distinguished by the habit of epiphytic tufts of erect filaments, the basal axial cells tapering to endophytic rhizoids, whorls of four whorl-branchlets which are simple or only slightly branched, with gland cells on the rachides, gonimolobes with elongate sterile cells at their base, and tetrasporangia borne on several cells of the rachides.


AGARDH, J.G. (1892). Analecta Algologica. Acta Univ. lund. 28, 1–182, Plates 1–3.

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

Author: H.B.S. Womersley & E.M. Wollaston

Publication: Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
©State Herbarium of South Australia, Government of South Australia


1. Thallus tufts occurring on the margins of receptacles of Platythalia angustifolia; axial cells usually with 2 whorl-branchlets at right angles

H. platythaliae

1. Thallus tufts arising from within the cortex of Cystophora spp.; axial cells with usually 4 similar whorl-branchlets


2. Epiphytic on Cystophora siliquosa; whorl-branchlets (3–) 4–6 cells long

H. episiliquosum

2. Epiphytic on Cystophora platylobium; whorl-branchlets (5–) 8–12 cells long


3. Whorl-branchlets usually unbranched, mostly 8–12 cells long; tetrasporangia pedicellate

H. muelleri

3. Whorl-branchlets usually branched, 5–10 cells long; tetrasporangia sessile

H. sessile

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