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Order Ulvales

Family Ulvaceae

Ulva Linnaeus

Mature thallus flattened or tubular/hollow. In the former comprising two cell layers, in the latter comprising a single cell layer (including most species formerly assigned to Enteromorpha). Thalli variously shaped, sometimes perforated or with dentate margins. Growth mainly by marginal cell division. Attachment by rhizoidal cells. Rhizoidal cells running between layers of blade in basal region of thallus. Life history usually comprising alternation of isomorphic diploid sporophytes (producing asexual, quadriflagellate zoospores) and haploid gametophytes (producing biflagellate gametes), but parthenogenesis recorded in some species.

The genus Ulva formerly consisted of entities with distromatic blades and the genus Enteromorpha of entities with tubular monostromatic thalli. However, Hayden et al. (2003), using molecular methods, showed that they cannot be separated at the generic level, and the older name, Ulva, now applies.

Over 500 species have been described, mainly based on thallus shape and size, but studies have shown that these characters are strongly affected by environmental conditions. At present some 98 species are accepted (Guiry & Guiry, 2012), of which we recognize 11 on the South African south coast. Current molecular studies indicate that several of the names we apply here are likely to change, but for the time being we base our descriptions on existing morphological understanding, and largely follow Stegenga et al. (1997).

Records of several species of Enteromorpha/Ulva from the South African south coast are for various reasons difficult to substantiate, and we have not attempted to document them here. Enteromorpha bulbosa (Suhr) Montagne was recorded by Barton (1893), but not reported since. E. lingulata J.Ag. was recorded from Hluleka by Bolton & Stegenga (1987), but the name is “uncertain”, as is the name Enteromorpha multiramosa Bliding (Guiry & Guiry, 2012).

 

Key to species

1a. Mature thallus tubular

2

1b. Mature thallus sheet-like

8

2a. Thallus unbranched

3

2b. Thallus branched

4

3a. Thallus thread-like; less than 50 µm in diameter

U. torta

3b. Thallus bladder-like; tubular to cuneiform

U. intestinalis

4a. Thallus sparsely branched near base; up to 10 mm tall; cup-shaped to peltate

U. tanneri

4b. Mature thallus at least several cm long

5

5a. Laterals arising near base of; and reaching same length as; main axis

U. flexuosa

5b. Most or all laterals shorter than main axis

6

6a. Axes profusely branched; many branches short and spine-like

U. clathrata

6b. Axes sparsely to profusely branched; spine-like branches absent

7

7a. Laterals mainly from proximal thallus; in section cells 12-17 µm high; square to slightly higher than broad

U. prolifera

7b. Laterals also from mid and distal parts of thallus; in section cells 15-30 µm high; 2-4 x higher than broad

U. compressa

8a. Thallus sheet-like; distromatic; blades broadly ligulate; margins with double dentation

U. rhacodes

8b. Thallus sheet-like; distromatic; double dentation absent

9

9a. Thallus deeply incised; forming several narrow (1-3 cm wide) ribbon-like blades

U. fasciata

9b. Thallus ovate to irregulary shaped; entire or variously incised

10

10a. Thallus stiff especially near base; basal margins with minute teeth; blade ca. 75 µm thick near apex

U. rigida

10b. Thallus up to a few cm tall; rosette-like; blade 35-40 µm thick near apex

U. uncialis

 

References genus Ulva :

Barton, E.S. 1893. A provisional list of the marine algae of the Cape of Good Hope. Journal of Botany, London, 31: 53-56, 81-84, 110-114, 138-144, 171-177, 202-210.

Bolton. J. J. & H. Stegenga (1987). The marine algae of Hluleka (Transkei) and the warm temperate/sub-tropical transition on the east coast of southern Africa. Helgoländer Meeresuntersuchungen 41: 165-183.

Burrows, E.M. (1991). Seaweeds of the British Isles. Volume 2. Chlorophyta. pp. [i]-xi, [1]-238, 60 figs, 9 pls. London: Natural History Museum Publications.

Hayden, H.S., Blomster, J., Maggs, C.A., Silva, P.C., Stanhope, M.J. & Waaland, J.R. (2003). Linnaeus was right all along: Ulva and Enteromorpha are not distinct genera. European Journal of Phycology 38: 277-294

 

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.