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Electronic Flora of South Australia Genus Fact Sheet
Phylum Magnoliophyta – Subphylum Seagrasses – Class Liliopsida – Subclass Alismatidae – Order Potamogetonales – Family Cymodoceaceae
Dioecious; perennials, rhizomatous, forming extensive meadows. Rhizomes much-branched, sympodial, lignified, with 1–2 roots at each node, producing numerous erect stems. Roots branched, lignified, wiry, often somewhat coiled. Stems lignified, wiry, marked by the annular scars of fallen leaves. Leaves alternate, distichous, borne in tufts at the ends of branches; sheath compressed, ligulate and auriculate, amplexicaul, leaving an annular scar on the stem when shed; blade flat linear, entire, shed with its sheath; veins inconspicuous, longitudinal veins 8–21, more or less parallel, joined irregularly by numerous oblique crossveins. Squamules present in the axil of each leaf. Tannin cells numerous. Flowers solitary and terminal on short lateral shoots, enclosed by normal (unmodified) vegetative leaves. Male flower subtended by a bract, subsessile at first, becoming pedicellate; 2 anthers, connate in their lower part, each with 2 pairs of microsporangia, dehiscing longitudinally, crowned by 2–3 appendages, anthers caducous at or immediately prior to dehiscence; pedicel elongating just prior to anthesis. Pollen grains filiform, individual grains up to 5 mm long, coiled into tight pollen masses. Pollination hydrophilous. Female flower consisting of 2 free carpels (usually one aborts) subtended by a circular bract which is initiated as a ring meristem but later becomes frayed (McConchie, Ducker & Knox 1982, p. 254) and may be very reduced in A. griffithii. Each carpel has a short style, and 3 (rarely more) stigmatic branches, and 4 (sometimes more) pericarpic lobes at the base of the ovary. The pericarpic lobes are fleshy at first, but a hard bony skeleton of more or less parallel bristles united at the base is revealed as the fleshy tissue disintegrates. These bristles form the 4–1obed "comb" which acts as a "grappling apparatus" (see Tepper 1882, p. 4) to anchor the young seedling to the substrate. Seedlings viviparous; almost immediately after fertilisation the seed germinates on the parent plant and develops into a leafy shoot which remains attached for about 7–12 months. The abscission layer forms immediately below the comb prior to the release of the seedling. The seedling is free floating until the grappling apparatus becomes caught in, and attached to, a substrate such as sand, an algal turf, a coralline alga or the fibrous leaf base of a Posidonia plant.
Type species: Amphibolis zosteraefolia C. Agardh = A. antarctica (Labillardière) Sonder & Ascherson ex Ascherson (Ducker, Foord & Knox 1977, p. 68).
Taxonomic notes: Two species, both endemic to southern Australia.
Black (1913, p. 3) was the first to accurately describe and illustrate the unique mode of reproduction and dispersal of Amphibolis. Recent studies by Ducker, Foord & Knox (1977), Ducker, Pettit & Knox (1978) and McConchie, Ducker & Knox (1982) have considerably enlarged our knowledge of the biology of the genus.
Huge mounds of drift often occur on beaches near Amphibolis meadows. These result both from branches torn off by storms and also from the vast quantities of lower leaves shed each winter. Sometimes marine balls are formed by wave action rolling fragments of Amphiholis stems into more or less spherical balls mostly up to about 7 cm in diameter. Amphibolis balls incorporate algal epiphytes, hydroids and other drift but are mostly composed of short lengths of Amphibolis stems (c.f. Posidonia balls (Pl. 16 figs 2,3) composed mainly of Posidonia fibres).
References:
AGARDH, C.A. (1823). Species Algarum, Vol. 1. (Lund.)
BLACK, J.M. (1913). The flowering and fruiting of Pectinella antarctica (Cymodocea antarctica). Trans. R. Soc. S. Aust. 37, 1–5, 1 Plate.
DUCKER, S.C., FOORD, N.J. & KNOX, R.B. (1977). Biology of Australian Seagrasses: the genus Amphibolis C. Agardh (Cymodoceaceae). Aust. J. Bot. 25, 67–95.
DUCKER, S.C., PETTIT, J.M. & KNOX, R.B. (1978). Biology of Australian Seagrasses: Pollen development and submarine pollination in Amphibolis antarctica and Thalassodendron ciliatum (Cymodoceaceae). Aust. J. Bot. 26, 265–285.
McCONCHIE, C.A., DUCKER, S.C. & KNOX, R.B. (1982). Biology of Australian Seagrasses: floral development and morphology in Amphibolis (Cymodoceaceae). Aust. J. Bot. 30, 251–264.
TEPPER, J.G.O. (1882). Some observations on the propagation of Cvmodocea antarctica Endl. Proc. R. Soc. S. Aust. 4, 1–4, 1 Plate.
The Marine Benthic Flora of Southern Australia Part I complete list of references.
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
KEY TO SPECIES OF AMPHIBOLIS
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1. Leaf blade flat, usually twisted about 180° in the upper half; apex truncate or lunate with 2 acute marginal teeth; blade L/B | A. antarctica |
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1. Leaf blade flat, not twisted, or only by | A. griffithii |
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