Electronic Flora of South Australia Genus Fact Sheet
Phylum Magnoliophyta – Subphylum Seagrasses – Class Liliopsida – Subclass Alismatidae – Order Potamogetonales – Family Potamogetonaceae
Annual or perennial, submerged rhizomatous herbs. Rhizomes monopodial. Roots 1–2 per node, unbranched; root-hairs abundant. Stems very short or absent, or up to 2.5 m long and flexuous with branches in one plane. Leaves alternate (except the 2 immediately below the inflorescence which are sub-opposite); sheath open, edges overlapping, eligulate, auriculate; blade narrow-linear to filiform, more or less concavo-convex in cross section with a large air canal either side of an inconspicuous median vein. Prophylls commencing each branch, always inserted between the branch and the main axis. Squamules paired, laterally opposed in each leaf axil. Tannin cells present in most tissues, particularly conspicuous in the epidermis as dark-brown elongate cells. Inflorescence a spike of (1–) 2 flowers on opposite faces of the axis, enclosed at first in the inflated sheathing leaf bases; peduncle short, stout, erect, or elongating greatly before anthesis to a fine thread raising the flowers to the water surface, and becoming tightly spirally coiled retracting the developing fruits after pollination. Flowers bisexual; perianth absent; stamens 2; anthers each with 2 bilocular pollen sacs, longitudinally dehiscent; pollen grains elongate-reniform with a reticulate exine; pollination hydrophilous (either below or on the water surface). Carpels (2–) 4–12 (–26), free, sessile or subsessile at first, often becoming stalked in the fruit; ovary ovoid, 1-celled; stigma sessile, thick, peltate. Fruit an achene, not floating, sessile or with a distinct stalk (podogyne) which remains attached to the fruit and falls with it. Exocarp spongy, disintegrating; endocarp bony, beaked, persistent, with a triangular depression either side of the base of the beak. Turions (starch-filled perennating organs) produced terminally on the rhizomes, or at the junction of the leaf sheath and rhizome, are present in 2 species.
Type species: Ruppia maritima Linnaeus.
Taxonomic notes: Two to ten species in temperate and subtropical regions throughout the world, in both ephemeral and permanent water bodies. Two species occur in marine habitats in southern Australia. In some localities Ruppia spp. are known as "Widgeon grass".
Ruppia is tolerant of a wide range of salinity, occurring in fresh, brackish, marine and sometimes in hypersaline situations to ten times the salinity of seawater (Brock 1982a). Some morphological variations appear to be associated with fluctuations in the environment (Brock 1981, 1982a, 1982b).
In Ruppia, pollination may occur either below, or on, the water surface. After detailed studies Setchell (1946) concluded that the genus (as known then) contained two species distinguished on the inflorescence position at pollination, and the associated peduncle length, viz. R. maritima Linnaeus with a short peduncle, permanently submerged inflorescence and pollination below water, and R. spiralis Linnaeus ex Dumortier [= R. cirrohosa (Petagna) Grande] with an elongate flexuous peduncle, elevating the inflorescence on to the water surface for pollination. Verhoeven (1979, p. 253) demonstrated that the submerged pollination in R. maritima takes place at the air-water interface of a gaseous bubble liberated from the air canals of the plant itself. The cosmopolitan R. maritima, although not common in Australia, has been recognized by Jacobs & Brock (1982) from all mainland States in permanent inland waters (i.e. salt lakes, mound springs and artesian bores) and also from estuaries in subtropical and tropical regions of Australia. There are no marine collections of this species from southern Australia but it has been found in Sydney Harbour, e.g. Parramatta, N.S.W. (Betche, Nov. 1881; NSW, 2437).
* R. polycarpa (Fig. 15A–C), first described from New Zealand (Mason 1967), is common in southern Australia in fresh to brackish water and also in salinities up to 66‰ (see Brock 1982a, p. 221), occurring in coastal lakes, lagoons and estuaries. R. polycarpa has filiform leaves less than 0.5 mm broad with obtuse or acute apices, flowers with (4–) 6–8 (–16) carpels, and fruits 2–3 mm long on slender straight podogynes mostly 1–2 cm long. Turions are frequently produced.
Selected Specimen: Peel Inlet, W. Aust., in freshwater 30 m from sea (Carstairs, 12.ix.1982; ADU, A53396).
R. polycarpa may be difficult to distinguish from R. tuberosa unless fruits are present. It has not been found in normal marine situations.
BROCK, M.A. (1981). The ecology of halophytes in the south-east of South Australia. Hydrobiologia 81, 23–32.
BROCK, M.A. (1982a). Biology of the salinity tolerant genus Ruppia L. in saline lakes in South Australia. 1. Morphological variation within and between species and ecophysiology. Aquat. Bot. 13, 219–248.
JACOBS, S.W.L. & BROCK, M.A. (1982). A revision of the genus Ruppia (Potamogetonaceae) in Australia. Aquat. Bot. 14, 325–337.
LINNAEUS, C. (1753). Species Plantarum. Vols 1, 2. (Laurenti Salvii: Stockholm.)
MASON, R. (1967). The species of Ruppia in New Zealand. N.Z. .1. Bot. 5, 519–531.
SETCHELL, W.A. (1946). The genus Ruppia L. Proc. Calif Acad. Sci. ser. 4. 25, 269–478.
VERHOEVEN, J.T.A. (1979). The ecology of Ruppia-dominated communities in western Europe. I. Distribution of Ruppia representatives in relaton to their autecology. Aquat. Bot. 6, 197–268.
The Marine Benthic Flora of Southern Australia Part I complete list of references.
Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
©Board of the Botanic Gardens and State Herbarium, Government of South Australia
KEY TO SPECIES OF RUPPIA
2. Mature fruiting carpel sessile or subsessile; podogyne absent or, if present, always much shorter than the carpel; carpels (6–)
2. Mature fruiting carpel with a well-developed podogyne; podogyne straight, slender, mostly
State Herbarium of South Australia