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Order Ulvales

Family Ulvaceae

Ulva rigida C.Agardh 1823: 410

Plants pale to grass green, up to 30 cm tall, irregularly incised or lobed, consistency firm, especially near the base; thallus margins near the base with minute teeth. Cells in surface view organized in long curved rows, rounded angular, 10-16 µm in diameter. Thickness of lamina from 75 µm in the apical region to 100 µm in the mid-thallus and increasing to 200 µm in the upper basal region. Cell height 25-35 µm , cells 2-4 times higher than broad, cylindrical with rounded angles at the outer periclinal wall. Chloroplast parietal, located against the outer periclinal cell wall or shifted to one of the radial cell walls; pyrenoids 1-3. Rhizoidal cells larger and darker than normal vegetative cells, in older plants forming ribs on the membrane surface.

Description from Stegenga et al. (1997).

Collections, ecology and regional distribution

Recorded from the Cape Peninsula to northern Kwazulu-Natal (16-58). Found from the shallow sublittoral to upper eulittoral.

World distribution: widespread in temperate and tropical seas, including East Africa (Guiry & Guiry 2013).

Type locality: Cadiz, Spain (Silva et al. 1996).

Note: Although Stegenga et al. (1997) considered this species to include South African records of U. uncialis (Kützing) Montagne, this is not supported by recent molecular evidence (L. Kandjengo, pers. comm.).


Ulva rigida, Arniston

Ulva rigida, herbarium specimens from a jetty in Knysna Lagoon

Ulva rigida, surface view of cells (cells each ca 15 µm in diameter)

Ulva rigida, XS showing cell shape and size

Ulva rigida. 1, Habit (fig, 2 typical of U. uncialis-like habit). 3, Surface view showing cell arrangement. 4, Longitudinal section of basal thallu. 5, Section of middle thallus. Drawings from Stegenga et al. 1997.


References Ulva rigida

Agardh, C.A. (1823). Species algarum rite cognitae, cum synonymis, differentiis specificis et descriptionibus succinctis. Volumen primum pars posterior. pp. [vii-viii], [399]-531. Lundae [Lund]: ex officina Berlingiana.

Guiry, M.D. & Guiry, G.M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 20 May 2013

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. and 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.