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Electronic Flora of South Australia Species Fact Sheet

Ulva rigida C. Agardh 1823: 410.

Phylum Chlorophyta – Order Ulvales – Family Ulvaceae

Selected citations: Bliding 1968: 546, figs 6–9. Koeman & van den Hoek 1981: 37, figs 78–107. Papenfuss 1960: 305, fig. 4.

Thallus (Fig. 44D) grass-green, lighter above, usually epilithic, sometimes epiphytic (e.g. on Posidonia), 10–30 (–40) cm high and across, usually with a single frond from the holdfast, plane to irregularly divided or lacerate above, often perforate; intact margin in some places with slight to prominent microscopic, multicellular spines (Fig, 45G), occasionally almost entire, surface smooth. Cells in surface view in rows in both directions, more irregular below, isodiametric to slightly elongate, (8–) 12–18 (–25) µm across in both upper and lower parts, with 1–2 pyrenoids (Fig. 451, J). Thallus 35–55 µm thick in upper parts with cells in transection rounded to avoid (Fig. 45H) and 12–18 µm high; 80–100 thick in mid parts with cells L/B 2–3, 25–35 (–40) µm high, and usually tapering from their base (centrally in thallus) to their outer end (Fig. 451); thallus just above rhizoidal region 100–200 µm thick, 120–200 µm thick near the base with cells L/B 2.5–4 (–5) and 40–50 µm long, and tapering outwardly, and with a central mass of dense rhizoids.

Reproduction: Reproduction (Bliding 1968, p. 550) isomorphic with the sporophyte producing quadriflagellate zoo(meio)spores and the gametophytes unisexual with biflagellate anisogametes.

Type from Cadiz, Spain; in LD (Herb. Agardh, 14294).

Selected specimens: Hardwicke Bay, York Pen., S. Aust., in lower eulittoral pools (Womersley, 9.xi.1980; ADU, A51844). Port Stanvac, S. Aust., eulittoral pool on ramp (Engler & Clarke, 21.x.1980; ADU, A51816). Rosetta Bay, Victor Harbor, S. Aust., uppermost sublittoral (Womersley, 19.vii.1980; ADU, A51253-"Marine Algae of southern Australia" No. 216). Yilki, Victor Harbor, S. Aust., near-shore pool area (Womersley, 26.x.1980; ADU A51821).

Distribution map based
on current data relating to
specimens held in the
State Herbarium of SA

Distribution: Widely distributed in temperate (especially warm) seas.

In southern Australia, from Hardwicke Bay, Yorke Pen., S. Aust. to Swan Bay, Vic. (probably more widely distributed), usually in sheltered to moderate wave action habitats.

Taxonomic notes: U. rigida is characterised by the irregularly divided thallus without elongate ruffled branches, a margin with microscopic spines where it is intact (often near the base, sometimes above, and usually only evident on parts of the thallus), cells in the upper thallus rather rounded in transection and those in older parts elongate and tapering from the centre to the outside in transection.

Specimens with the above characteristics agree well with Bliding's concept of U. rigida, and this is one of the more easily recognized species of Ulva on the cell features. However, the description and illustration of the type specimen by Papenfuss (1960, p. 305, fig. 4) do not show the elongate, outwardly tapering cells of older parts of the thallus and further checking of the type specimen is needed to establish whether these features are present or not.


AGARDH, C.A. (1823). Species Algarum, Vol. 1. (Lund.)

BLIDING, C. (1968). A critical survey of European taxa in Ulvales, II. Ulva, Ulvaria. Monostroma, Kornmannia. Bot. Notiser 121, 535–629.

KOEMAN, R.P.T. & VAN DEN HOEK, C. (1981). The taxonomy of Ulva (Chlorophyceae) in the Netherlands. Br. phycol. J. 16, 9–53.

PAPENFUSS, G.F. (1960). On the genera of the Ulvales and the status of the order. J. Linn. Soc. Bot. 56, 303–318, Plates 1–6.

The Marine Benthic Flora of Southern Australia Part I complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
Part I
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

Illustrations in Womersley Part I, 1984: FIGS 44D, 45 G–J.

Figure 44 image

Figure 44   enlarge

Fig. 44. A. Ulva lactuca (ADU, A42338). B. Ulva australis, on Amphibolis (ADU, A51817). C. Ulva australis (ADU, A51819). D. Ulva rigida (ADU, A51821).

Figure 45 image

Figure 45   enlarge

Fig. 45. A–C. Ulva lactuca (ADU, A52029). A. Surface and cross section views of young thallus. B. Ditto, of mid thallus. C. Ditto, rhizoidal region near base. D–F. Ulva australis (ADU, A51819). D. Surface and cross section views of young thallus. E. Ditto, of mid thallus. F. Cross section view of rhizoidal region near base. G–J. Ulva rigida (ADU, A51816). G. Thallus margin with spines. H. Cross section view of young thallus. I. Surface and cross section views of mid thallus. J. Surface view of rhizoidal region near base.

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