Neotropical Cymodoceaceae

Anna Haigh 

Royal Botanic Gardens, Kew, UK. 


Habit: Herbs, marine aquatics, submerged, perennial; rhizomes present, creeping. Leaves alternate (distichous), simple, with open basal sheath and small ligule, numerous axillary intravaginal squamules present; stomata and trichomes absent. Inflorescences borne at end of short erect shoots, usually of solitary flowers, rarely in cymes. Flowers unisexual (plants dioecious); perianth absent. Staminate flowers: sessile or stalked; androecium with 2 stamens, the stamens fused back to back with apical prolongation. Pistillate flowers: gynoecium apocarpous, the ovaries superior, the carpels 2, the styles long, slender, often branched, the stigmas inconspicuous in Halodule Endl. or of two stigmatic stout stylodia in Syringodium Kütz.; placentation apical, the ovules 1 per carpel. Fruits indehiscent, small; endocarp stony.

Notes on delimitation

  • The Cymodoceaceae are placed in the Alismatales in the APGIII classification system.
  • They were previously placed in the Najadales by Dahlgren et al (1985) and also by Cronquist (1981).

Distribution in the Neotropics

A sub cosmopolitan family of 5 genera and c.16 species.  Two genera comprising 5 species occur in the Neotropics.

  • Halodule (4 species in Neotropics).
  • Syringodium (1 species in Neotropics).

Distinguishing characters (always present)

Number of genera

See above

Useful tips for generic identification

Key to genera of Neotropical Cymodoceaceae

1. Leaf blade distinctly terete; many flowers in conspicuous cymose inflorescences … Syringodium
1. Leaf blade linear, flat; inflorescence 1-flowered or 2 flowers resembling a single flowerHalodule


  • Native.

General notes

  • Commonly known as sea-grasses or manatee grasses.
  • Cymodoceaceae occur in shallow, coastal, tropical or subtropical waters.
  • They can form extensive submarine meadows in shallow, clear waters with minimal wave action.
  • Some are important in the stabilization of shallow marine sediments, nutrient recycling, and as food sources for grazing marine animals.

Important literature

Cronquist, A. 1981. An Integrated System of Classification of Flowering Plants. Columbia University Press, New York.

Dahlgren, R. M. T., Clifford, H. T., & Yeo, P. F. 1985. The Families of the Monocotyledons. Springer, Berlin.

Hartog, C. Den, 1970. The sea-grasses of the world. Verhandl. Kon. Ned. Akad. Wetensch. Nat. 59(1): 1-275.

Kuo, J. & McComb, A.J. 1998. Cymodoceaceae. In: K. Kubitzki (ed.), The families and genera of vascular plants 4: 133-140. Springer Verlag, London.

Stevenson, D.W., 2004. Cymodoceaceae. Pp. 433-434. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds.). Flowering Plants of the Neotropics. New York Botanical Garden, Princeton University Press, Princeton.

How to cite

Haigh, A. (2009). Neotropical Cymodoceaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics.