Cymodoceaceae Vines
  • Stud. Text-book Bot. 2: 553 (1895) nom. cons.


This taxon is accepted by eMonocot

General Description

Marine plants, perennial, dioecious, glabrous; rhizome creeping; vessel elements absent. Leaves distichous or spiral; leaf-sheath amplexicaul, with 2 apical auricles, ligulate; blade linear with several parallel nerves, in between which tannin dots and dashes are visible. Flowers terminal and solitary on a short branch, or in cymose inflorescences, sessile or stalked, small, water-pollinated; tepals absent. Staminate flowers consisting of 2 anthers, these 4-locular, partially connate, dehiscing by extrorse slits; pollen thread-like, without exine. Pistillate flowers of 2 free ovaries; ovule 1, pendulous. Fruit an indehiscent nutlet; seed 1; endosperm absent.

Notes: Obermayer in F.S.A. (1966) follows Hutchinson and treats this as part of the Zannichelliaceae; den Hartog in Sea-grasses of the World (1970) follows Ascherson and treats this as a subfamily {i}Cymodoceoideae{/i} of the Potamogetonaceae. Current consensus is on separate family status.

Perennial marine herbs with creeping, monopodially or sympodially branched rhizomes. Roots often branched, with few to many root hairs. Leaves alternate, distichously arranged, with distinct blade, sheathing base and a ligule between sheath and blade; sheath after being shed leaving an open or closed circular scar on stem; blade linear, flat or terete; tannin cells numerous; stomata absent. Squamules present in each leaf axil. Inflorescence cyrnose or flowers solitary. Flowers dioecious, naked, enclosed by leaflike bracts; male flowers subsessile or pedicellate, with 2 tetrasporangiate stamens; female flowers of 2 free ovaries, each with a long stylulus which is unbranched or divided into 2-3 filiform stigmatic stylodia; carpels I-ovulate; usually only 1 carpel developing into fruit. Fruit indehiscent; seeds germinating on parent plant in Amphibolis and Thalassodendron.

Afamily of5 genera and 16 species ofseagrasses, largely in tropical and subtropical waters of the Indo-West Pacific and Caribbean, but extending into warm-temperate Australia and the Mediterranean.

Ecology

The family is wholly marine and generally subtidal, in water from 0.5 to 40 m deep; some species (including C. serrulata and T. ciliatum) extend into the intertidal. The plants often form extensive meadows of single or mixed species on sandy or muddy substrates. T. pachyrhizum usually grows on rocks, and S. isoetifolium is normally found among other species, and does not form meadows.

Vast meadows, mainly of Amphibolis, occur at Shark Bay, W Australia, where stabilisation of sediments by seagrasses, and production of calcareous skeletal material from epiphytes and infauna has produced striking changes in submarine geology, and the effective isolation from the open ocean of large areas of water (Walker 1985). The plants are of great importance to nutrient cycling and detrital food webs in nearshore environments. There is also direct grazing, notably by turtles and dugongs (Phillips and McRoy 1981; Larkum et al. 1989).

Distribution

Members of the family are largely tropical and subtropical, apart from Amphibolis and Thalassodendron pachyrhizum from warm-temperate, southern and SW Australia respectively, and Cymodocea nodosa from the Mediterranean. There is a rich centre for the family in the Indo-West Pacific including Australia (all five genera), and a secondary centre in the Caribbean (two genera). Most species have a wide distribution, but T. pachyrhizum and C. angustata are restricted to certain areas of W Australia.

Uses

The significance of the group is substantial, especially in areas where large meadows occur. It lies in the stabilisation of sediments, in nutrient cycling, in supporting grazing dugong and turtles, and, probably most significant ofall, in the support of food webs through the production of organic detritus. These food webs presumably underlay the important fisheries of regions where seagrasses dominate submarine plant biomass.

  Bibliography

  • 1 Henk Beentje (2002) Cymodoceaceae. Flora of Tropical East Africa
  • 2 Vines(1895). Stud. Text-book Bot.
  • 3 Kuo, J. & McComb, A.J. Cymodoceaceae. Flowering Plants. Monocotyledons: Alismatanae and Commelinanae (except Gramineae) 133-140 (1998).
  • 4 Vines, S.H. Original publication of Cymodoceaceae. (1895).

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Flora of Tropical East Africa (FTEA)
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