Neotropical Alismataceae

Emerson Ricardo Pansarin

Universidade de São Paulo, FFCLRP, SP, Brazil. 

Description

Perennial, rarely annual aquatic, laticiferous herbs. Roots fibrous, sometimes adventitious. Stem short, sometimes corm -like rhizomes or pseudostolons present. Leaves basal, alternate, spiral or in two ranks, sessile or petiolate, simple, sheathing at base, emergent or more rarely submerged or sometimes with floating blade; petiole terete to triangular between whorls; blade with pellucid marking in some species of Echinodorus Rich. & Engelm. ex A.Gray and Helanthium (Benth. & Hook.f.) Engelm. ex J.G.Sm.. Inflorescence scapose, usually raceme-like or panicle-like cymes with numerous whorls along a complex system of branches, sometimes umbellate through reduction to one whorl or sometimes reduced to a solitary flower. Flowers hermaphrodite or unisexual (then plants monecious or dioecious), actinomorphic, hypogynous, 3-merous, with perianth differentiated into sepals and petals; sepals 3, free, persistent, sometimes coriaceous and with longitudinal ribs (Echinodorus and Helanthium); petals 3, free, delicate, usually white, rarely pink, sometimes with a yellow or purple spot at the base; stamens 6 to numerous, filaments distinct, anthers extrorse, rimose; gynoecium apocarpous, with 3 to many carpels distributed along a convex receptacle, carpels generally 1-ovulate and with basal placentation, stigma apical or with a lateral or gynobasic persistent style. Fruit an achene or more rarely a follicle, sometimes with longitudinal ribs (Echinodorus and Helanthium). Seeds U-shaped, with or without glands, endosperm absent.

Notes on delimitation

  • Some authors, based on morphological and molecular analysis, include both genera Limnocharis Bonpl. and Hydrocleys Rich. (Limnocharitaceae) within Alismataceae sensu lato, but this is not a consensus.
  • According to Lehtonen and Myllys (2008), only Limnocharis is nested within Alismataceae .
  • Furthermore, in the most treatments Limnocharitaceae and Alismataceae have been considered as distinct families because Alismataceae sensu stricto form a monophyletic group.

Distribution in the Neotropics

  • Alismataceae includes 12 genera and about 80 species distributed among tropical and subtropical regions of both hemispheres.
  • Three genera occur in the Neotropics: Sagittaria Rupp. ex L., Echinodorus and Helanthium (a genus segregated from Echinodorus).
  • The center of diversity of Echinodorus is the Neotropical region. All species of this genus occur in the Neotropics.
  • Helianthium is a genus endemic to the Neotropics, occurring mainly in South America.
  • Sagittaria is a genus distributed predominantly in the western hemisphere, with about 12 species occurring in the Neotropics. Some North American species are cultivated as pond ornamental plants.

Distinguishing characters (always present)

Alismataceae are distinguishable on the basis of the presence of:

  • Laticifers.
  • The stomata with parallel division.
  • The pollen grains commonly 2-porate to polyporate.
  • The embryo strongly curved.

Other important characters

Key differences from similar families

Alismataceae can be distinguished from Limnocharitaceae on the basis of:

  • Their white or pink flowers (vs. yellow flowers in Limnocharitaceae).
  • Generally one ovule per carpel (vs. many ovules per carpel).
  • Basal placentation (vs. laminar placentation).
  • Presence of achenes (vs. follicles).

Useful tips for generic identification

Key to genera of Neotropical Alismataceae

1. Rhizomatous herbs. Inflorescence a raceme-like or panicle-like cyme or a panicle-like cyme with several whorls … 2
1. Pseudostoloniferous herbs. Inflorescence umbelliform with up to three whorls. Flowers hermaphrodite with 6 or more rarely 9 stamens and 10-20 carpels. Achenes with 3-4 longitudinal ribs … Helanthium

2. Flowers hermaphrodite or pistillate (gynodioecious species), with numerous stamens, versatile anthers, and more than 20 carpels. Achenes ribbed, not wingedEchinodorus
2. Flowers unisexual (monoecious plants), sepals without longitudinal ribs, with numerous stamens, basifixed anthers, and more than 20 carpels. Achenes not ribbed, wingedSagittaria

Status

  • All three genera occurring in the Neotropics are native.

General notes

  • Some native species includes aquarium and pond ornamental plants.
  • Some species of Sagittaria have an edible rhizomatous stem.
  • Leaves of Echinodorus grandiflorus are used in popular medicine.
  • Pollen collecting bees pollinate many species of Echinodorus. Sagittaria and some species of Echinodorus present floral nectaries. The floral nectar is secreted from the base of petals, stamens or carpels.

Important literature

Fassett, N.C. 1955.  Echinodorus in the American tropics. Rhodora 57: 133-156, 174-188, 202-212.

Haynes, R.R. & Holm-Nielsen, L.B. 1985.  A generic treatment of Alismatidae in the Neotropics with special reference to Brazil. Acta Amazônica, Suppl. 15: 153-193.

Haynes, R.R. & Holm-Nielsen, L.B. 1986.  191. Alismataceae. In: G. Harling & L. Andersson (eds.) Flora of Ecuador 26: 1-24.

Haynes, R.R. & Holm-Nielsen, L.B. 1994.  The Alismataceae. Flora Neotropica Monogr. 64: 1-112.

Haynes, R.R. & Holm-Nielsen, L.B. 1995.  Alismataceae. In: P.E. Berry, B.K. Holst & K. Yatskievych (eds.). Flora of Venezuelan Guayana. 2: 377-383.

Lehtonen, S. 2006.  Phylogenetics of Echinodorus (Alismataceae) based on morphological data. Botanical Journal of the Linnean Society 150: 291-305.

Lehtonen, S. & Myllys, L. 2008.  Cladistic analysis of Echinodorus (Alismataceae): simultaneous analysis of molecular and morphological data. Cladistics 24: 218-239.

Lot, H.A. & Novelo, R.A. 1994.  Alismataceae. In: G. Davidse, M. Souza S. & A.O. Chater (eds.) Flora Mesoamericana  6: 3-8. México, D. F.: Universidad Nacional Autonoma de México.

Pansarin, E.R. & Amaral, M.C.E., 2005.  Alismataceae. In: M.G.L. Wanderley, G.J. Shepherd, A.M. Giulietti & T.S. Melhem (eds.) Flora Fanerogâmica do Estado de São Paulo. Rima, São Paulo, pp. 1-10.

Pansarin, E.R. 2008.  Reproductive biology of Echinodorus longipetalus (Alismataceae): sexual morphs, breeding system and pollinators Aquatic Botany 89: 404-408.

Rataj, K. 1978.  Alismataceae of Brazil. Acta Amazônica, Supl. 8: 1-53.

Rogers, G.K. 1983.  The genera of Alismataceae in the Southeastern United States. Journal of Arnold Arboretum 64: 383-420.

Seubert, M. 1847.  Alismataceae. In: C.F.P. Martius & A.G. Eichler (eds.) Flora Brasiliensis. 3(1): 101-112, tabs. 12-16. Typographia Regia, Monachii.

How to cite

Pansarin, E.R. (2009). Neotropical Alismataceae. 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/Alismataceae.htm.