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Order Gigartinales

Family Plocamiaceae

Plocamium Lamouroux

Plants with a more-or-less-developed holdfast of prostrate axes bearing several erect axes which may be terete, compressed or flattened; erect axes often complanate. Branching is sympodial, producing an alternate series of simple and/or compound laterals (branchlets), compound laterals repeating the branching pattern. The number of simple and /or compound laterals is generally characteristic of each species. Growth is apical, the central filament of the uniaxial thalli remaining visible in some species. The central filament lies within a pseudoparenchymatous medulla of large cells and a cortex of smaller cells. Reproductive structures develop on the ultimate and penultimate laterals or on adventitious branches in the axils of laterals. Tetrasporangia develop on modified branchlets (stichidia) in double rows, and are zonately divided. Cystocarps spherical, without ostiole.

The genus is cosmopolitan, and 39 species are recognised worldwide, among which 10 occur in South Africa (Guiry & Guiry 2009). We have recorded 8 species on the South African south coast.

Key to species

1a. Erect axes 5 mm wide or wider

P. corallorhiza

1b. Erect axes 3 mm wide or narrower

2

2a. Pectinate series of laterals comprising up to 6 (-10) branchlets, lower branchlet often compound

P. glomeratum

2b. Pectinate series of laterals comprising no more than 4 branchlets

3

3a. Erect axes terete throughout, pectinate series of laterals comprising 1 simple and 1 compound branchlet

P. cornutum

3b. Erect axes flattened or compressed throughout or at least in distal parts

4

4a. Erect axes rather membranous, up to 3 mm wide, pectinate series of laterals comprising 1 simple and 2-3 compound branchlets, stichidia (if present) terminal on compound branchlets

P. maxillosum

4b. Erect axes less than 3 mm wide

5

5a. Pectinate series of laterals generally comprising 2-4 branchlets (1 simple and 1, 2 or 3 compound)

6

5b. Pectinate series of laterals consisting of 2 branchlets (1 simple, 1 compound)

7

6a. Plants delicate, less than 0.5 mm wide, axes zig-zagging somewhat

P. beckeri

6b. Plants rather robust, to 1 mm wide, profusely branched, young laterals slightly

P. rigidum

7a. Simple lateral branchlets in pectinate series narrowly triangular, less than 0.5 mm wide at base, with smooth margins

P. telfairiae

7b. Simple branchlets broadly triangular, often more than 1 mm wide at base, outer edge sometimes slightly serrated

P. suhrii

 

References Plocamium

Guiry, M.D. & Guiry, G.M. 2009. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched June 2009.

 

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 September 2018.