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Heterothamnion platythaliae Athanasiadis 1996: 186, figs 95–97.

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Heterothamnieae

Thallus (Fig. 75A) in dense spreading tufts 3–5 mm high, with numerous erect axes, each axial cell bearing (1–) 2 whorl-branchlets. Attachment by rhizoids (Fig. 75B) from erect axes, penetrating the host edges, probably at conceptacles; epiphytic on Platythalia angustifolia. Structure. Apical cells 12–16 µm in diameter and L/D 1–1.5, enlarging rapidly to axial cells 50–80 µm in diameter and L/D 1.5–2.7, tapering and with shorter cells near the base. Whorl-branchlets (Fig. 75C) one or two per axial cell, if two situated usually at right angles and alternating on successive cells, with one of the 2 often more branched than the other and with 2–4 branches from the basal or upper cells; whorl-branchlets 200–500 µm and 6–10 cells long, basal cells slightly longer than next outer cell, 25–40 µm in diameter and L/D 1.2–1.6 (–2), tapering to terminal cells 12–22 µm in diameter and L/D 1–1.5, ends rounded; gland cells apparently absent. Lateral branches borne on the basal cell of whorl-branchlets. Cells probably uninucleate; rhodoplasts discoid.

Reproduction: Gametophytes probably monoecious. Carpogonial branches borne on the basal cells of reduced 2-celled whorl-branchlets which may continue growth. Carposporophytes (Fig. 75C) terminal, surrounded by 4 whorl-branchlets, with rounded gonimolobes 100–200 .1.n1 across of ovoid carposporangia 20–25 µm in diameter. Spermatangia on small branched clusters on the adaxial side of lower cells of whorl-branchlets shortly below the carposporophytes.

Tetrasporangia (Fig. 75D) borne on lower cells of whorl-branchlets, sessile, subspherical, 30–40 in diameter, tetrahedrally divided.

Type from Sarge Bay, Cape Leeuwin, W. Aust., on Platythalia angustifolia, drift (Woelkerling, 16.xi.1968; AD, A34205-"Marine Algae of southern Australia" No. 387). Holotype in GB, isotypes distributed from AD.

Distribution map based
on current data relating to
specimens held in the
State Herbarium of SA

Distribution: Only known from the type collection.

Taxonomic notes: H. platythaliae is based on AD material and is only known from the type.

It is very doubtful if this species is correctly placed in Heterothamnion, since it differs significantly from the other species in number (1 or 2) and arrangement of whorl-branchlets.


ATHANASIADIS, A. (1996). Morphology and classification of the Ceramioideae (Rhodophyta) based on phylogenetic principles. Opera Botanica No. 128, pp. 1–216.

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

Illustration in Womersley Part IIIA, 1998: FIG. 75.

Figure 75 image

Figure 75   enlarge

Fig. 75. Heterothamnion platythaliae (AD, A34205). A. Tufts on Platythalia angustifolia. B. Rhizoidal base of a tuft, penetrating the edge of the host. C. Branches with whorl-branchlets and young carposporophytes. D. Axes with whorl-branchlets bearing tetrasporangia.

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