Electronic Flora of South Australia Genus Fact Sheet

Genus GELIDIUM Lamouroux 1813: 128, nom. cons.

Phylum Rhodophyta – Class Florideophyceae – Order Gelidiales – Family Gelidiaceae

Thallus 0.2–30 cm long, usually much branched, with a discoid or hapteroid holdfast and often with prostrate stolons attached by rhizoidal clumps, bearing erect branches; firm and cartilaginous. Structure uniaxial with a more or less conspicuous apical cell, differentiating into a medulla of numerous, similar, longitudinal filaments and often hyphae, sometimes forming a reticulum, and a compact cortex 2–5 cells thick of small, ovoid cells (inner cells becoming radially elongate) each with several small rhodoplasts; rhizines usually abundant in the outer medulla and inner cortex, between the elongate inner cortical cells.

Reproduction: Carpogonia sessile on inner cortical cells or intercalary, arising near branch apices, accompanied by short filaments of small nutritive cells; carposporophyte developing on both sides of the central placental layer of cells and thus within a bilocular chamber, forming terminal carposporangia, with the pericarp developing a small ostiole on each side of the swollen cystocarp. Spermatangia formed in surface patches near ends of ramuli, from spermatangial initials replacing or cut off from outer cortical cells.

Tetrasporangia formed in sori near the ends of ramuli or small branchlets (sometimes stichidioid), cut off laterally from cortical cells and when mature lying in the inner cortex or outer medulla, usually decussately cruciately divided (often irregularly so).

Life history triphasic with isomorphic tetrasporophytes and gametophytes, the latter usually dioecious; sexual plants rare or unknown in some species.

Type species: G. corneum (Hudson) Lamouroux 1813: 129, typ. cons. [= Gelidium sesquipedale (Clemente) Thuret in Bornet & Thuret 1876: 61].

Taxonomic notes: A genus of numerous species, widely distributed in temperate oceans. Gelidium and Pterocladia are basically separated on cystocarp structure, on the number of ostioles, and on the position of the placenta (Santelices 1991). Rodriguez & Santelices (1988) have suggested that two vegetative characters are useful: species of Gelidium have slightly protruding apical cells in acute apices whereas the broad apices of Pterocladia have the apical cell slightly sunken in a shallow apical notch. In Gelidium the cortical cells in surface view are rounded and irregular in arrangement near the base of axes, whereas in Pterocladia they are slightly elongate and more or less in lines. The situation of the apical cell is probably correlated with the degree of flattening of the branch just below the apex. These vegetative differences are not considered significant by Norris (1992a).

References:

BORNET, E. & THURET, G. (1876). Notes algologiques. Fasc. 1. (Masson: Paris.)

LAMOUROUX, J.V.F. (1813). Essai sur les genres de la famille des thalassiophytes non articulées. Ann. Mus. Hist. Nat., Paris 20, 21–47, 115–139, 267–293, Plates 7–13 (1–7).

NORRIS, R.E. (1992a). A proposed phylogenetic scheme for the Gélidiales. In Abbott, I.A. (Ed.), Taxonomy of Economic Seaweeds. With reference to some Pacific and Western Atlantic species. Vol. III, pp. 151–171. (Calif. Sea Grant College Program: La Jolla, Calif.)

RODRIGUEZ, D. & SANTELICES, B. (1988). Separation of Gelidium and Pterocladia on vegetative characters. In Abbott, I.A. (Ed.), Taxonomy of economic seaweeds. With reference to some Pacific and Caribbean species. Vol. II, pp. 115–125. (Calif. Sea Grant College Program: La Jolla, Calif.)

SANTELICES, B. (1991). Variations in Cystocarp Structure in Pterocladia (Gélidiales: Rhodophyta). Pacific Sci. 45, 1–11.

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

Author: H.B.S. Womersley & M.D. Guiry

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 GELIDIUM

1. Thallus 5–30 cm high, erect, much branched, with axes 0.5–2.5 mm broad

2

1. Thallus 0.2–3 cm long, erect and turf-like or mat-like, sparingly to much branched, with axes or branches 100–500 (–1500) µm thick or broad

3

2. Branching irregular and distant (not pinnate); stichidia on all surfaces (or tending to two sides) of terete to slightly compressed branches, crowded

G. asperum

2. Branching regularly pinnate for 3–4 (–5) orders; stichidia largely marginal as terete to compressed ramuli

G. australe

3. Erect branches terete, 100–200 (–300) rim in diameter, slightly branched; tetrasporangial sori terminal or on short laterals near branch apices, compressed, occasionally becoming intercalary by further growth of the branch apices; outer cortical cells 4–8 (–10) µm across in surface view

G. crinale

3. Erect branches compressed to flat above, 200–1000 (–1500) rim broad, simple to subpinnately branched; outer cortical cells 3–5 rum across

G. pusillum


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