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Order Ceramiales

Family Rhodomelaceae

Laurencia Lamouroux

Plants erect, a few to 40 cm tall; holdfasts discoid, rhizoidal or encrusting; thallus branching profuse to sparse, polystichous to regularly bilateral; branches compressed to terete. Axes polysiphonous but forming several layers of pseudoparenchymatous tissue; four pericentral cells present; axial and periaxial (pericentral) cells clearly visible in some species; branch apices with terminal sunken pit, trichoblasts usually present. Outer cortical cells without secondary pit connections, containing one to many intracellular colourless inclusions (corps en cerise) these visible only in fresh material, the number per cell characteristic for each species. Medullary cell walls with lenticular thickening in some species. Reproductive structures usually on terminal branchlets, sometimes on main axes. Tetrasporangial initials arising from pericentral cells, tetrasporangia sub-cortical, arrangement sometimes species-specific. Cystocarps protruberant, ostiolate.

The genus Laurencia is one of six genera in the Laurencia complex, the other five being Palisada, Chondrophycus, Laurenciella, Osmundea, and Yuzurua ((Nam et al. 1994, Garbary & Harper 1998, Nam 2007, Martin-Lescanne et al. 2010 and Cassano et al. 2012). Laurencia sensu stricto is the largest of these genera, with 145 species currently recognised (MD Guiry in Guiry & Guiry 2017).

Francis (2014), reported that “the species count for the South African Laurencia complex is now fourteen Laurencia species, three Palisada species, and one species each in the genera Chondrophycus and Laurenciella”. See Francis et al. (2017) for further descriptions of new South African Laurencia species: only those that occur on the south coast are included here.

Note: Although Laurencia obtusa has been recorded from the south coast (e.g. Stegenga et al. 1997), the study of Francis et al. (2017) shows that it does not occur here, and specimens that were given this name are probably either L. pumila ssp. dehoopiensis or Laurencia cf. corymbosa.

Key to south coast species

 

1a. Axes and laterals slightly to strongly compressed

2

1b. Axes and laterals terete

4

2a. Axes strongly compressed, oppositely branched

L. complanata

2b. Axes slightly compressed, alternately to irregularly branched

3

3a. Axes irregularly alternately branched, outer cortical cells with 1-3 corps en cerise

L. flexuosa

3b. Axes alternately branched, outer cortical cells with 5-6 corps en cerise

L. alfredensis

4a. Plants entirely olive-green, caespitose

L. griseaviolacea

4b. Plants entirely a shade of red to purple or with some red, pink or purple on the thallus

5

5a. Plants entirely a shade of red to purple (essentially one colour)

6

5b. Plants bi-coloured

9

6a. Primary laterals spirally arranged, higher order laterals whorled or alternate

L. glomerata

6b. Branching polystichous, alternate to opposite or subverticillate in higher order laterals

7

7a. Plants epiphytic , subtidal, ultimate branches wart-like

L. pumila ssp dehoopiensis

7b. Plants epilithic

8

8a. Plants to 15 cm tall, axes to 1.5 mm diameter, fertile terminal branchlets corymbose

L. cf corymbosa

8b. Plants to 4 cm tall, axes to 0.5 mm diameter, laterals mostly adaxially arranged

L. digitata

9a. Main axes up to 1.5 mm in diameter, plants olive becoming purple distally, sparsely branched

L. pumila

 9b. Main axes up to 1 mm in diameter

9

10a. Plants with pyramidal outline

L. natalensis

10b Plants tufted to caespitose, no pyramidal outline

L. multiclavata

References Laurencia

Cassano, V., Oliveira, M.C., Gil-Rodriguez, M.C., Senties, A., Diaz-Larrea, J., and Fujii, M.T. 2012. Molecular support for the establishment of the new genus Laurenciella within the Laurencia complex (Ceramiales, Rhodophyta). Botanica Marina. 55 (4) pp. 349 – 357.

Francis, C.M. 2014. Systematics of the Laurencia complex (Rhodomelaceae, Rhodophyta) in southern Africa. PhD Thesis, University of Cape Town, 199 pp.

Francis, C.M., Bolton, J.J, Mattio, L. Mandiwana-Neudani T.G., and Anderson R.J. 2017. Molecular systematics reveals increased diversity within the South African Laurencia complex (Rhodomelaceae, Rhodophyta). Journal of Phycology 53: 804-819.

Garbary, D.J. and Harper, J.T. 1998. A phylogenetic analysis of the Laurencia complex (Rhodomelaceae) of the red algae. Cryptogamie Algologie 19 pp. 185 – 200.

Gil-Rodriguez, M.C., Sentìes, A., Dìaz-Larrea, J., Cassano, V. and Fujii, M.T. 2009. Laurencia marilzae sp. nov. (Ceramiales, Rhodophyta) from the Canary Islands, Spain, based on morphological and molecular evidence. Journal of Phycology. 45 pp. 264 – 271.

Guiry, M. D. in Guiry, M.D. & Guiry, G.M. 2017. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 11 August 2017.

Martin-Lescanne, J., Rousseau, F., De Reviers, B., Payri, C., Couloux, A., Cruaud, C. and Le Gall, L. 2010. Phylogenetic analyses of the Laurencia complex (Rhodomelaceae, Ceramiales) support recognition of five genera: Chondrophycus, Laurencia, Osmundea, Palisada and Yuzurua stat. nov. European Journal of Phycology, 45 (1) pp. 51 – 61.

Nam, K.W., Maggs, C.A. and Garbary, D.J. 1994. Resurrection of the genus Osmundea with an emendation of the generic delineation of Laurencia (Ceramiales, Rhodophyta). Phycologia 33(5) pp. 384-395.

Stegenga, H., Bolton, J.J. & Anderson, R.J. 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, http://southafrseaweeds.uct.ac.za; Accessed on 24 September 2018.