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Order Gigartinales

Family Caulacanthaceae

Caulacanthus ustulatus (Turner) Kützing 1843: 395

Thalli forming dense, tangled, brown clumps or turfy patches 1-3 cm high and usually up to several cm in diameter. Axes about 1 mm diameter, frequently and irregularly branched, apices spiny. Axes often secondarily attached to substrata or other axes by pads formed from outgrowths of cortical tissue. Structure uniaxial, each cell of central filament bearing two pericentral cells at more-or-less right angles; these divide dichotomously to produce a filamentous medulla and cortex and a compact epidermis of small (4-6 µm diameter) cells. Tetrasporangia (70 x 25 µm) zonately divided and scattered in cortex. Carposporophytes develop sub-terminally in branch tips; mature cystocarps form globose swellings with latero-apical ostiole.

Collections, ecology and regional distribution

Found around the whole SA coast (1-58). Common in the mid and lower eulittoral, forming brown, mossy clumps; often associated with mussels.

World distribution: Very widespread in temperate, subtropical and tropical waters.

Type locality: Lectotype locality is Cádiz, Spain (Silva et al. 1996).

Note: Searles (1968) details the morphology and reproduction of this species.


Caulacanthus ustulatus, Keurboomstrand, forming typical cushions in upper eulittoral zone.

Caulacanthus ustulatus, detail of branches.

Caulacanthus ustulatus, xs showing anatomy including zonately-divided tetrasporangia (Nature’s Valley material).

Caulacanthus ustulatus. 1. Habit (detail of plant). 2. Longitudinal section near thallus apex. 3. Cross sections (ca = central filament). 4. Tetrasporangia. Reproduced from Stegenga et al. (1997).


References Caulacanthus ustulatus

Kützing, F.T. 1843. Phycologia Generalis. Leipzig 458 pp., 80 pls.

Searles, R.B. 1968. Morphological studies of red algae of the order Gigartinales. University of California Publications in Botany 43: 100 pp.

Silva, P.C., Basson, P.W. & Moe, R.L. 1996. Catalogue of the benthic marine algae of the Indian Ocean. University of California Publications in Botany 79: 1-1259.

Stegenga, H., Bolton, J.J. & R. J. Anderson. 1997. Seaweeds of the South African west coast. Contributions from the Bolus Herbarium 18: 655 pp.


Cite this record as:

Anderson RJ, Stegenga H, Bolton JJ. 2016. Seaweeds of the South African South Coast.
World Wide Web electronic publication, University of Cape Town,; Accessed on 26 February 2024.