Electronic Flora of South Australia Genus Fact Sheet

Genus SARCOTHALIA Kützing 1849: 739

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Gigartinaceae

Thallus much branched pinnately to subdichotomously, in some species foliose, 2–100 cm high, branches compressed, somewhat mucilaginous and drying cartilaginous. Structure multiaxial, with a compact cortex of anticlinal, subdichotomous filaments of small cells, larger inwardly, and a medulla of anastomosing filaments orientated at random or with the central ones more or less longitudinal and interlinked.

Reproduction: Sexual thalli monoecious or dioecious. Carpogonial branches 3-celled, borne on inner cortical (supporting) cells of lesser branches or in surface papillae. Procarpic, with the supporting cell acting as auxiliary cell following fertilization, producing numerous gonimoblast initials which develop mainly thallus inwardly, with the cells cutting off laterally small clusters of carposporangia; enveloping tissue present, sometimes with transverse absorbing gonimoblast filaments. Cystocarps swollen, appearing stalked in lesser branches or in papillae on foliose thalli. Spermatangia in inconspicuous sori, cut off from outer cortical cells.

Tetrasporangial sori maculate, lying deep in the medulla, developing tetrasporangia in short chains of 2–4 cells from clusters of inward growing medullary filaments, cruciately divided. Tetraspores released by gelatinous extrusion through a central pore in the wall.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Type species: S. burmannii (C. Agardh) Kützing 1849: 739 [= S. stiriata (Turner) Leister in Hommersand et al. 1993: 112].

Taxonomic notes: Sarcothalia is restricted to the cold temperate oceans of the Southern Hemisphere (Australia, New Zealand and South Africa) and has only recently been resurrected as a genus within the Gigartinaceae (Hommersand et al. 1993). It is characterised by emergent cystocarps, whether in papillae on foliose species or in lesser branches in branched species, and by the location of the tetrasporangial sorus deep within the medulla with the tetrasporangia derived from clusters of inward growing medullary filaments.

Hommersand et al. (1993) in circumscribing Sarcothalia identified the distinctive nature of tetrasporangial development. Tetrasporangia typically occur in small, maculate sori within the mid medulla, with the tetrasporangia developing as chains of 2–4 cells cut off from a small cluster of inward growing secondary filaments, the cells of which link progressively with adjacent (mainly inwards) medullary cells. In contrast to species of Gigartina, the tetrasporangial sorus is not liberated as a unit on maturity, with the tetraspores generally being released by gelatinous extrusion through a central pore in the wall. Erosional surfaces are generally absent.

Hommersand et al. (1993) further characterised carposporophyte development in Sarcothalia, emphasising the compact nature of the enveloping tissue, and the enlarged cells of the inner gonimoblast filaments which may become linked by secondary pit-connections at maturity. These gonimoblast filaments displace the envelope which forms a distinct boundary penetrated only by tubular gonimoblast cells. Carposporophyte development is essentially similar in southern Australian species of Sarcothalia, with S. insidiosa and S. crassifolia agreeing very well with the generic description. However, S. radula appears distinctive in possessing a diffuse enveloping tissue without transverse gonimoblast filaments.

References:

HOMMERSAND, M.H., GUIRY, M.D., FREDERICQ, S. & LEISTER, G.L. (1993). New perspectives in the taxonomy of the Gigartinaceae (Gigartinales, Rhodophyta). Hydrobiologia 260/261 (Proc. Intn. Seaweed Symp. 14), 105–120.

KÜTZING, F.T. (1849). Species Algarum. (Leipzig.)

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

Author: K.S. Edyvane & H.B.S. Womersley

Publication: Womersley, H.B.S. (14 January, 1994)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIA, Bangiophyceae and Florideophyceae (to Gigartinales)
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIA 1994, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

KEY TO SPECIES OF SARCOTHALIA

1. Fronds foliose, broadly lanceolate to irregularly ovate, usually branched only from a short stipe; cystocarps in simple or branched papillae scattered over the surface and margins

S. radula

1. Thallus non-foliose, pinnately or irregularly branched; branches basally constricted; cystocarps subterminal or marginal in branchlets, involucrate or not

2

2. Thallus entangled, clumped or pulvinate, 2–6 (–10) cm high and 2–10 cm across, with some erect branches, alternately pinnate, axes 2–4 (–5) mm broad, often arched, tapering to slender apices; apices forming haptera attaching to the substratum

S. insidiosa

2. Thallus erect, 8–30 cm high, branches strongly compressed, alternately pinnate, axes (3–) 5–15 mm broad, 1–1.5 mm thick, tapering to pinnules 4–12 mm long and 1–2 mm broad

S. crassifolia


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