Neotropical Elatinaceae

Victor W. Steinmann

Instituto de Ecología, A.C., Centro Regional del Bajío, Pátzcuaro, Mexico. 

Description

Shrubs or herbs (annual or perennial), often aquatic or semiaquatic, with resinous latex, glabrous or pubescent with uni- or multicellular, unbranched trichomes, these sometimes gland -tipped, stems often rooting at the nodes. Leaves opposite or whorled, submerged in some of the aquatic species, stipules present, interpetiolar, free, small, scarious, lamina simple, entire, serrate or crenulate, multicellular extrafloral glands often present along leaf margins, pinnately veined. Flowers solitary or in few-flowered axillary cymes, small, actinomorphic, hermaphroditic, disk absent, sepals 2-5(6), imbricate, free or connate in lower half, petals 2-5(6), imbricate, free, persistent, stamens opposite the sepals, of same number or twice as many as sepals, free, equal, anthers bithecal, dorisfixed, versatile, introrse, with longitudinal dehiscence, pollen tricolporate, ovary superior, 2-5(6)-locular, locules connate, each with numerous ovules, anatropous, placentation axillary or basal, styles same number as locules, short, free, apical, stigma capitate, papillose. Fruit capsular, with septicidal dehiscence. Seeds numerous, exarillate, without endosperm, embryo straight or curved, cotyledons short. X=6 or 9.

Notes on delimitation

  • Elatinaceae contains only two genera: Elatine L. and Bergia L. 
  • The family has historically been considered closely related to the Clusiaceae.  However, recent molecular phylogenetic studies suggest that it is sister to Malpighiaceae, in the order Malpighiales.

Distribution in the Neotropics

  • Elatine: Approximately seven aquatic species distributed sporadically throughout the Neotropics mostly in high-elevation, temperate, standing bodies of waters but rarely in tropical or subtropical habitats at lower elevations.
  • Bergia: Two aquatic to semiaquatic species with limited distribution in the Neotropics and a third species approaching the area: B. capensis L., a native to southern Africa, is occasionally naturalized in tropical wetlands in at least Cuba, Mexico, Peru and Ecuador; the little-known B. arenaroides Fenzl is endemic to Brazil; although not known from the Neotropics proper, B. texana Seub. ex Walp. approaches the region in subtropical northern Mexico, with extralimital records from the states of Sonora and Tamaulipas.

Distinguishing characters (always present)

Other important characters

  • Aquatic or semiaquatic herbs (at least in the Neotropical species).

Key differences from similar families

  • Elatine can be confused with various other aquatics having reduced, inconspicuous flowers, but is distinguished by the combination of opposite, stipulate leaves; flowers with 2 to 4 petals and sepals and a superior ovary; and septicidal capsules with numerous reticulate seeds.

Number of genera

  • Two: Bergia and Elatine.

Useful tips for generic identification

Key to genera of Neotropical Elatinaceae

1. Flowers with 5 (6) sepals and petals; sepals possessing a conspicuous mibrid, apex acute and often with a sharp tip ... Bergia
1. Flowers with 2-4 sepals and petals; sepals without a distinct midrib, apex obtuse... Elatine

Notable genera and distinguishing features

See above.

Status

  • Both genera are native to the Neotropics; Bergia has an additional naturalized species.

General notes

  • Some members of Elatine are cultivated in aquaria, and a few species of Bergia employed in traditional medicine.  Otherwise the family is of little economic importance.
  • The introduced Bergia capensis L. occurs in various low elevation wetland sites, including rice fields.  It is noteworthy in possessing dimorphic roots, with those of plants growing in water being chlorophyllous and free floating whereas those of terrestrial plants being white and sturdy.
  • The majority of the nearly 25 species of Bergia occur in the Old World, with the center of diversity in southern Africa.
  • Elatine is widely distributed throughout the world, with most of its 25 species occurring in the northern hemisphere.
  • Although the Neotropical species are strictly aquatic to semiaquatic herbs, some Old World species of Bergia are shrubs that occur in arid environments.

Important literature

Bacigalupa, N.M. 1970. Observaciones sobre el género Elatine en la Argentina. Darwiniana 16: 106-115.

Davis, C.C. & M.W. Chase. 2004. Elatinaceae are sister to Malpighiaceae; Peridiscaceae belong to Saxifragales. Amer. J. Bot. 91: 262-273.

Hunziker, A.T. 1970. Sobre una nueva hidrófita argentina: Elatine lorentziana nov. sp. Lorenzia 1: 5-10.

Lægaard, S. 2008. Elatine rotundifolia sp. nov. (Elatinaceae) from Ecuador. Nordic J. Bot. 26: 235-236.

Macbride, J.F. 1941. Elatinaceae, Flora of Peru. Field Mus. Nat. Hist., Bot. Ser. 13: 3-4.

Molau, U. 1983. Elatinaceae. In: G. Harling and L. Andersson (eds). Flora of Ecuador 20, pp. 17-23.  Department of Plant and Environmental Sciences, University of Gothenburg.

Niedenzu, F. 1925. Elatinaceae. In: A. Engler and K. Prantl (eds). Die Natürlichen Pflanzenfamilien (ed. 2) 21: 270-276.

Novelo R., A. & J.H. Wiersema. 2000. Tres nuevos registros para México de plantas acuáticas vasculares. Acta Bot. Mex. 51: 53-60.

Schmidt-Mumm, U. & H.Y. Bernal. 1995. A new species of Elatine (Elatinaceae) from the Colombian páramos in the northern Andes. Brittonia 47: 27-30.

Tucker, G.C. 1986. The genera of Elatinaceae in the southeastern United States. J. Arnold Arbor. 67: 471-483.

How to cite

Steinmann, V.W. (2009). Neotropical Elatinaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Elatinaceae.htm.