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Electronic Flora of South Australia Species Fact Sheet

Ochmapexus minimus (Harvey) Womersley, comb. nov.

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Radiathamnieae


Callithamnion minimum Harvey 1863, synop.: Iv. Sonder 1881: 11.

Thallus (Fig. 106A, B) medium to dark red, 500–1500 µm high, complanately branched with distinctive pectinate, adherent and non-adherent, holdfasts; epiphytic, mainly on Caulerpa longifolia. Structure. Main axes curved to straight (Fig. 106A), lateral branches often unilateral on the upper side of the curved axis (Fig. 106B), axial and lateral branch cells bearing a single or often two opposite branchlets (Fig. 106A, B), simple or similarly branched. Axial cells 27–45 µm in diameter and L/D 1.2–1.8, basally shorter, cells of laterals decreasing to 14–20 µm in diameter and L/D 1.2–2 in mid thallus, then to 8–12 µm in diameter and L/D (1–) 2–4 in apical cells of branchlets. Holdfast (Fig. 106C) 80–180 µm across, with two rows of isodiametric cells from the basal axial cell and lying in the plane of the thallus, each cell bearing an elongate cell (with a separate sheath) which divides (occasionally to 2–3 cells) especially on contact with the host and adheres; unattached holdfasts occur frequently on upper branches of the thallus. Cells uninucleate; rhodoplasts elongate to ribbon like, few per cell.

Reproduction: Gametophytes little known. Possible spermatangial development (Fig. 106B, D) consists of short, branched, rows of smaller isodiametric cells 3–6 µm across on upper thallus cells, but one case also with tetrasporangia.

Tetrasporangia (Fig. 106E, F) on short branchlets, first terminal and with further potential tetrasporangia developing singly or in opposite pairs from 1–2 cells below the mature sporangium, sessile, subspherical to slightly ovoid, 21–34 µm in diameter, tetrahedrally divided.

Type from Port Fairy, Vic., on Caulerpa longifolia (Harvey, Alg. Aust. Exsicc. 525D); lectotype sheet in Herb. Harvey, TCD.

Selected specimens: Pennington Bay, Kangaroo I., S. Aust., on Chaetomorpha coliformis, sublittoral fringe (Womersley, 29.xii.1948; AD, A10769) and on Caulerpa longifolia, drift (Womersley, 22.viii.1954; AD, A19748). Abalone Cove, West I., S. Aust., on Plocamium cartilagineum, 5 m deep (Kildea, 20.x.1996; AD, A66709). N of Cape Thomas, S. Aust., on C. longifolia, drift (Womersley, 24. viii.1960; AD, A24374). Carpenters Rocks, S. Aust., on C. longifolia, 3–5 m deep (Shepherd, 4.xii.1968; AD, A32991). Lady Julia Percy I., Vic., on Halopteris, 8–13 m deep (Shepherd, 5.i.1968; AD, A32319). Flinders, Vic., on Polysiphonia decipiens, drift (Kraft 7065, 27.x.1979; MELU). Gabo I., Vic., on hydroid, 1–3 m deep (Shepherd, 15.ii.1973; AD, A43380). Lady Bay, Southport, Tas., on Chondria incrassata, 1–5 m deep (Womersley & Brown, 28.x.1982; AD, A53690).

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

Distribution: Bay, Kangaroo I., S. Aust., to Gabo I., Vic., and SE Tasmania.

Taxonomic notes: O. minimus occurs particularly on Caulerpa longifolia where vast numbers of plants may be present, and is also known on a variety of other hosts. Most plants are sterile, only few tetrasporangial and sexual thalli being known.

Callithamnion minimum was recorded from New Zealand, epiphytic on Caulerpa brownii, by Adams (1994, p. 250), but her description does not agree with the Australian species.


ADAMS, N.M. (1994). Seaweeds of New Zealand. (Cant. Univ. Press: Christchurch.)

HARVEY, W.H. (1863). Phycologia Australica. Vol. 5, Plates 241–300, synop., pp. i-lxxiii. (Reeve: London.)

SONDER, O.W. (1881). In Mueller, F., Fragmenta Phytographiae Australiae. Supplementum ad volumen undecinum: Algae Australianae hactenus cognitae, pp. 1–42, 105–107. (Melbourne.)

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

Author: H.B.S. Womersley

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. 106.

Figure 106 image

Figure 106   enlarge

Fig. 106. Ochmapexus minimus (A–D, AD, A 19748; E, F, AD, A24374). A. Branches with an unattached holdfast. B. Branches with small upper lateral cells. C. Holdfast. D. Upper branches with small lateral cells. E. Thallus with tetrasporangia. F. Branches with tetrasporangia.

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