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Order Ceramiales

Family Rhodomelaceae

Polysiphonia Greville

Plants filamentous, freely branched, with terete axes and branches, erect or partly prostrate; attachment of prostrate parts by rhizoids or haptera. Number of pericentral cells in genus varying between 4 and 24, fairly consistent for a species; secondary cortication present or absent. The origin of branches varies within the genus: 1) Exogenous – branches originate below the thallus apex, cut off from the central axial cell before any pericentral cells form. 2) Cicatrigenous – arising from the basal cell of a trichoblast. 3) Endogenous – originating from the central axial cells after the pericentral cells have formed.

A distinction between determinate and indeterminate laterals is clear in some species but absent in others. Trichoblasts may be present or absent in vegetative thalli. Tetrasporangia are formed in little-differentiated thallus sections, one per segment, in a straight series, each with two or three cover cells. Cystocarps are urceolate to globose. Antheridial stands are cylindrical or cylindro-conical.

Found almost worldwide in marine and estuarine environments: epilithic, epiphytic and epizoic, with 222 currently recognized species (MD Guiry in Guiry & Guiry 2016).

Note 1: Polysiphonia may be confused with other south coast genera such as Lophosiphonia, Neosiphonia and Pterosiphonia. However, Lophosiphonia has unlimited growth of dorsiventral prostrate branches and a limited system of uprights that develop endogenously, and Pterosiphonia has flattened, bilaterally symmetrical branches (Guiry & Guiry 2016). Neosiphonia differs from Polysiphonia in a number of characters (see Kim & Lee 1999). Morphological characters that are relatively easy to discern include: (in Neosiphonia) lateral branches arising on successive segments, erect indeterminate branches developing from the main axes and tetrasporangia in spiral series. In Polysiphonia lateral branch initials are separated by one to several segments, erect branches develop from a prostrate basal system, and tetrasporangia are “arranged in straight series on determinate branches” (Kim & Lee 1999).

Note 2: Polysiphonia subtilissima  Montagne 1840: 199

We have not seen this species, which is recorded by Lambert et al. (1987) from mangroves north of the Mbashe River to northern KwaZulu-Natal, and they describe it as follows: “Thallus less than 1 mm high, maroon, branching infrequent, polysiphnous throughout. Horizontal axes are attached by long unicellular rhizoids. Trichoblasts infrequent, colourless and unbranched. Four pericentral cells per axial cell.” (See Lambert et al. (1987, Fig. 4c and 4d). It is reported as associated with mangroves from certain estuaries including Xora (just north of the Mbashe River) to Kosi Bay in northern KwaZulu-Natal (45-58) (Lambert et al. 1987). They note that it is “a common associate of the bostrychietum”.

This species is reported from temperate and tropical localities, virtually worldwide in saline to estuarine habitats and even in some freshwater habitats (W. Guiry in Guiry & Guiry 2016). The type locality is Cayenne, French Guiana (Silva et al. 1996).

key to species

1a. Species with more than four pericentral cells


1b. Species with four pericentral cells


2a. Estuarine species, with 5 or 6 pericentral cells; some secondary cortication present (in older specimens)


2b. Species of full salinity, with ca. 8 pericentral cells

P. foetidissima

3a. Plants epilithic. 5 or 6 pericentral cells; axes branched every 4-10 segments. Every segment near the apices with a trichoblast

P. kowiensis

3b. Plants epi-/endophytic on (Codium sp.) 5 pericentral cells; axes scarcely branched, vegetative trichoblasts rare

Polysiphonia sp 1.

4a. Pericentral cells with chloroplasts on radial walls only

P. incompta (and see note on Polysiphonia  sp 3 under P. incompta)

4b. Pericentral cells with chloroplasts on radial and peripheral walls


5a. Plants mainly prostrate or with very well-developed prostrate system


5b. Plants with well-developed, branched erect axes


6a. Prostrate axes up to 65 µm in diameter and with down-curved tips, erect filaments in a dorsal row, unbranched or with a few short laterals

P. scopulorum

6b. Prostrate axes up to 175 µm in diameter and with upward-curving tips, erect filaments not in dorsal row, often with branches

P. namibiensis

7a. Filaments up to 50 µm wide, apices without trichoblasts

Polysiphonia sp 2

7b. Creeping filaments ca 200 µm wide, uprights 150-170 µm wide near middle, apices with trichoblasts

Polysiphonia sp 4

References Polysiphonia

M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2016. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 03 June 2016.

Kim, M.-S. & Lee, I.K. 1999. Neosiphonia flavimarina gen. et sp. nov. with a taxonomic reassessment of the genus Polysiphonia (Rhodomelaceae, Rhodophyta). Phycological Research 47: 271-281.

Lambert, G., Steinke T.D & Y Naidoo. 1987. Algae associated with mangroves in southern African estuaries. I. Rhodophyceae. South African Journal of Botany 53 (5): 349-361.

Montagne, C. 1840. Seconde centurie de plantes cellulaires exotiques nouvelles. Décades I et II. Annales des Sciences Naturelles, Botanique, Seconde Série 13: 193-207, pls 5, 6.

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.


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 24 September 2018.