South African Seaweeds

Order Gelidiales

Family Gelidiaceae

Gelidium Lamouroux

Thalli tough, small (about 10 mm) to large (up to 40 cm tall), red to reddish-brown to blackish, terete, compressed or flattened, sparsely to profusely branched. Holdfast of cylindrical or compressed, branched or unbranched, prostrate axes attached by rhizoidal haptera. Plants forming turfs or clumps, or solitary. Erect fronds often terete basally, becoming compressed or flattened distally. Structure uniaxial, apical cell small but distinct, cortex of anticlinal filaments visible in cross-section as several layers of small pigmented cells. Medulla filamentous, in cross-section showing large colourless cells interspersed with thick-walled rhizines that may also occur in inner cortical layers. Sporophytes producing sori with tetrasporangia or in some species, bisporangia, on apical branches or proliferations. Cystocarps bilocular, with ostioles on both sides, carposporangia borne on both sides of a septum dividing the cystocarp into two loculi.

A geographically widespread genus with representatives in temperate and tropical waters worldwide. At present 134 species are recognized worldwide (M. D. Guiry in Guiry & Guiry, 2015), 10 of which have been recorded on the South African south coast.

Key to the species

1a. Mature erect axes longer than 6 cm	2
1b. Mature erect axes shorter than 6 cm	5
2a. Main axes and laterals terete, usually less than 1 mm in diameter, secondary branches often unbranched	*G. abbottiorum*
2b. Main axes and laterals compressed or flattened, usually more than 1 mm wide, secondary branches branched	3
3a. Plants brownish to blackish, main axes usually more than 2 mm wide, blades proliferating from the midrib, margins toothed	*G. pristoides*
3b. Plants purplish-red to red, main axes usually less than 2 m wide, blades proliferating from margins only, margins not toothed	4
4a. Lateral branches mostly at right angles to axis, terminal branches seldom overlapping each other	*G. pteridifolium*
4b. Lateral branches forming an angle of up to 45^o with axis and often geniculate, branchlets often overlapping	*G. capense*
5a. Erect axes compressed to flattened, usually widening distinctly around origin of branches	*G. crinale*
5b. Erect axes terete, compressed or flatttened, not widening around branch origins	6
6a. Erect and prostrate axes cylindrical, about 250 µm diameter, only some apices of upright branches flattened	*G. arenarium*
6b. Erect axes largely or entirely flattened	7
7a. Erect axes flattened distally, with curled, twisted distal branches in up to 5 orders, plants up to 12 mm tall	*G. De Clerckii*
7b. Erect axes flattened, usually branched, distal branches not notably twisted	8
8a. Erect axes rarely simple, usually sparsely branched, branching distichous and irregular rather than pinnate, plants small (to 8 mm)	*G. isabelae*
8b. Erect axes at least in part with pinnate branches or pinnate marginal lobes	9
9a. Plants to 50 mm tall, foliaceous, erect axes pinnately branched	*G. micropterum*
9b. Plants 20 mm or smaller, with extensive prostrate system	10
10a. Prostrate and upright axes (if present) flattened, plants growing in limpet “gardens” in lower eulittoral/ sublittoral fringe	*G. micropterum*
10b. Prostrate axes cylindrical, uprights flattened throughout or distally	11
11a. Uprights flat, 1-2 mm wide and up to 10 mm high, often with pinnate marginal lobes, sporophytes bearing bisporangia	*G. foliaceum*
11b. Uprights lanceolate to ligulate, cylindrical basally, becoming flattened, about 1 mm wide and up to 20 mm high, branching irregular to pinnate, sporophytes bearing tetrasporangia	*G. reptans*

References Gelidium

Guiry, M.D. in Guiry, M.D. & Guiry, G.M. 2015. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 19 March 2015.

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 18 November 2024.