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Electronic Flora of South Australia Species Fact Sheet

Hirsutithallia abaxialis Wollaston & Womersley, sp. nov.

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Callithamnieae

Thallus (Fig. 122A) erect, medium grey-red, 1–5 cm high, with a main axis bearing radial laterals giving a broadly pyramidal form, cortication commencing close to apices. Holdfast 0.2–0.5 mm across, rhizoidal; epiphytic on Posidonia and Amphibolis. Structure. Ecorticate determinate branchlets 650–1500 µm long, subdichotomous or laterally branched (Fig. 122B) mainly abaxially with outer filaments slightly upwardly curved, basal cells 80–130 µm in diameter and L/D (1–) 1.2–1.6, tapering over 10–15 cells (the last 2–5 cells markedly smaller) to small, rounded, terminal cells 5–10 µm in diameter and L/D 2–3, often with terminal hairs. Axial cells of corticated branches increasing to 200–300 (–400) µm in diameter and L/D 1–1.5, becoming densely corticated by descending rhizoids from the basal cells of lateral branchlets, with most rhizoid cells bearing an outer anticlinal filament 3–6 (–7) cells and (45–) 60–120 (–150) µm long, simple or occasionally branched. Lateral branches arising on basal to mid cells of branchlets. Cells uninucleate, with no or few darkly-staining globules per cell; rhodoplasts discoid, ribbon like in older cells.

Reproduction: Gametophytes dioecious. Procarps borne on basal to mid cells of indeterminate laterals on ecorticate branchlets. Carpogonial branches borne on one of two opposite periaxial cells, with the carpogonium post-fertilization dividing longitudinally and each cell connecting via a small connecting cell with the auxiliary cells cut off from the two periaxial cells. Each auxiliary cell then divides to produce a gonimoblast initial which forms branched chains of cells enlarging to form pyramidal lobes (Fig. 122C, D) of ovoid carposporangia becoming 30–55 µm in diameter; involucre absent. Spermatangial clusters (Fig. 122E, F) are 60–130 µm across, borne on cells of the ecorticate branchlets, with a stalk cell bearing 2–4 (–5) cells from its outer end, each of which bears 1–3 further series of smaller cells, the terminal ones being spermatangia.

Tetrasporangia (Fig. 122G) are borne singly on cells of ecorticate branchlets, sessile, subspherical, 40–90 µm in diameter, tetrahedrally divided.

Type from Tiparra Reef, Spencer Gulf, S. Aust., on Posidonia sinuosa, 5 m deep (Shepherd, 30.ix.1970); holotype in AD, A37311.

Selected specimens: Tiparra Reef, Spencer Gulf, S. Aust., 5 m deep on Amphibolis (Shepherd, 30.ix.1970; AD, A37304), 11 m deep on Amphibolis (Shepherd, 5.xi.1971; AD, A38308) and 5 m deep on Posidonia australis (Shepherd, 13.vii.1971; AD, A39240).


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

Distribution: Only known from Tiparra Reef, S. Aust., on Posidonia and Amphibolis antarctica.

Taxonomic notes: H. abaxialis is named from the abaxial branching of many of the ecorticate branchlets. It differs from H. laricina in having longer ecorticate branchlets with basal cells of greater diameter, tapering markedly over the last 2–5 cells, and less branched carposporophytes with larger carposporangia. Collections at Tiparra Reef have been made from May to November.

References: The Marine Benthic Flora of Southern Australia Part IIIC

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. 122.

Figure 122 image

Figure 122   enlarge

Fig. 122. Hirsutithallia abaxialis (A–D, F, AD, A37311; E, G, AD, A38308). A. Habit, on Posidonia. B. Branches with corticated axis bearing ecorticate branchlets. C. Twinned carposporophyte. D. Axial cell bearing twinned carposporophytes. E. Branch with spermatangial clusters. F. Sectional view of a spermatangial clusters. G. Ecorticate branch with developing tetrasporangia.


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