Neotropical Juncaginaceae

Anna Haigh

Royal Botanic Gardens, Kew, UK. 

Description

Aquatic herbs, emergent, grass-like, underground rhizomes and erect stems usually present. Leaves alternate, basal, simple, sessile; tubular sheath present, adnate proximally to blade; ligule present at apex of sheath (a few millimeters long); blades linear, terete to dorsiventrally flattened. Inflorescences terminal on elongate scapes, spikes, solitary pistillate flowers present in Lilaea Bonpl. (in addition to spikes), these axillary. Flowers actinomorphic or zygomorphic, bisexual or sometimes unisexual in Liliaea (plants polygamous); perianth absent, or tepals 1, or 6 in 1-2 series, distinct; androecium of 1, 4, or 6 stamens, sometimes absent, the anthers sessile or subsessile; gynoecium weakly connate in Triglochin L., the ovaries superior, the carpels 3 or 6 (fertile) in Triglochin, or 1 in Lilaea, 3 sterile carpels alternating with fertile carpels when only 3 fertile carpels present (in Triglochin), the styles absent in Triglochin and present in Lilaea; placentation basal, the ovules 1 per carpel. Fruits schizocarps, the 3 or 6 fertile carpels eventually separating into 1-seeded nutlets, the nutlets 3-winged in Lilaea. Seeds solitary; embryo straight.

N.B. Lilaea has up to four types of flowers on one plant. These include perfect flowers with tepals present and the style 0.5-2 mm long or without tepals and the style 0.2-30 cm long. The latter type is solitary in the leaf axils. The remaining ones are in spikes.

Haynes 2004

Notes on delimitation

Distribution in the Neotropics

A subcosmopolitan family of 4 genera and c. 12 species.  Two genera comprising 4 species occur in the Neotropics, and one genus (Tetroncium Willd.) in southern South America.

  • Triglochin L.:  12 species, cosmopolitan, with about 4 species native to the coastal marshes of the Neotropics.
  • Lilaea:  monospecific (L. scilloides (Poiret) Hauman) native to temperate and tropical montane marshes, from Canada to Chile and Argentina.
  • Tetroncium Willd.:  monospecific (T. magellanicum Willd.) occurs outside the Neotropics, but in Tierra del Fuego, Patagonia, and the Falkland Islands.

Distinguishing characters (always present)

  • Aquatic herbs, emergent, grasslike.
  • Leaves basal, linear; sheath present.
  • Fruits schizocarps or nutlets.

Other important characters

  • Flowers with perianth absent, or tepals 1, or 6 in 1 or 2 series.
  • Inflorescences on scapes, terminal spikes or of solitary axillary flowers.

Useful tips for generic identification

Key to genera of Neotropical Juncaginaceae

1. Flowers both distally in scapose, spikelike racemes, these perfect, pistillate and staminate, and basally on the scape in leaf axils, these pistillate and 1-carpellate … Lilaea
1. All flowers distally in spikelike racemes; carpels 3, 4 or 6 … 2

2. Flowers 3-merousTriglochin
2. Flowers 2-merous; southern S. America …Tetroncium

Status

Native

General notes

  • The Juncaginaceae occupy a variety of habitats. Lilaea can be found in high mountain meadows of the Andes. Triglochin usually occurs in marshes that are brackish or have high concentrations of marl.
  • Plants are often extremely abundant in soils so heavily laden with marl or salts that the soil surface is white, especially on high plateaus.

Important literature

Haynes, R.R., 2004. Juncaginaceae. Pp. 452-453. 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.

Haynes, R.R., Les, D.H. & Holm-Nielsen L.B., 1998. Juncaginaceae. In: K. Kubitzki (ed.), The families and genera of vascular plants 4: 260-263.

How to cite

Haigh, A. (2009). Neotropical Juncaginaceae. 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/Juncaginaceae.htm.