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Order Ceramiales

Family Rhodomelaceae

Herposiphonia Nägeli

Thalli differentiated into long indeterminate axes and shorter, usually unbranched determinate laterals. Main axes usually prostrate. Branching pattern regular, usually with each segment bearing a lateral in repeating series of three determinate and one indeterminate branch (or branch primordium). Determinate laterals rarely with trichoblasts. All axes uncorticated, number of pericentral cells in the genus 6-18, range within each species narrower. Attachment rhizoids arising from ventral pericentral cells, usually developing terminal haptera or pads. Reproductive structures developing on determinate branchlets. Tetrasporangia usually one per segment, in straight series. Cystocarps lateral on determinate branchlets.

Species discrimination is based on number of pericentral cells, size and shape of branchlets and position of reproductive structures. See Wynne (1984) for an earlier account of the genus in South Africa. About 45 species of Herposiphonia are currently accepted taxonomically (Guiry & Guiry 2013), of which we record 5 species and one forma from the south coast. Another species, H. insidiosa, is widespread but seems indistinguishable from our H. falcata (see note under the latter species).

Key to species

 

1a. Cells in suprabasal segment of determinate laterals much longer than other cells

H. clavata

1b. Cells in suprabasal segment of determinate laterals similar length to other cells

2

2a. Determinate laterals dorsal, very sparse, arising usually only from every fourth segment of prostrate axes

H. secunda

2b. Determinate laterals arising from (almost) every segment of prostrate axes in series of three to each indeterminate lateral (or branch primordium)

3

3a. Determinate laterals relatively long (up to 50 segments), often rather straight, not congested, arranged in single dorsal row

H. secunda f. tenella

3b. Determinate laterals a maximum of 30 segments long, arranged either in dorsal row or arising alternately and dorso-laterally from indeterminate laterals

4

4a. Determinate laterals compressed, in single dorsal row, with maximum of 27 segments per lateral

H. prorepens

4b. Determinate laterals cylindrical, in one or roughly two lateral rows

5

5a. Determinate laterals with segments 0.3 times as long as broad, stout, blunt, with a maximum of 18 segments per lateral, tetrasporangia 2 per segment

H. didymosporangia

5b. Determinate laterals with segments 0.5-0.8 times as long as broad, maximum of 30 segments per lateral, tetrasporangia 1 per segment

H. falcata

 

References Herposiphonia

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

Wynne, M.J. 1984. Notes on Herposiphonia (Rhodomelaceae, Rhodophyta) in South Africa, with a description of a new species. Cryptogamie, Algologie 5: 167-177, 12 figs.

 

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, http://southafrseaweeds.uct.ac.za; Accessed on 20 November 2018.