Neotropical Polygonaceae

Efigênia de Melo and Flávio França

Universidade Estadual de Feira de Santana (UEFS), Brazil.  

Description

Herbs, shrubs, lianas (stem or tendril climbers) or trees; without latex or exudate. Stipules usually present, connate to form a leaf sheath (ochrea), rarely absent (subfam. Eriogoneoideae), leaf sheath tubular, membranaceous or scarious, deciduous or persistent, with bilobed or fringed margins. Leaves simple, alternate (rarely opposite), usually spirally arranged; petiolate or subsessile, petioles often flattened; extrafloral nectaries sometimes present at petiole base; leaf-blades entire, pinnately veined; basally auriculate, cordate, hastate, sagittate, rounded to cuneate, margins entire, sometimes crenate. Flowers usually hermaphrodite, small, if unisexual then plants monoecious, polygamo-monoecious or dioecious; inflorescence cymose, terminal, or in axillary racemes, corymbs, spikes and heads, sometimes in axillary fascicles; involucral bracts sometimes present, developed and showy, regular, 2-5-merous, cyclic to partially acyclic; hypanthium, when present, free, hypogynous disk or nectaries present between the androecial members; calyx and corolla distinct, or both sepal-like or petal-like, 2-6, free or joined, 1-2-whorled or spiralled, persistent in fruit and often accrescent; stamens (2-)6(-9) to many (Symmeria Benth.), free or adnate to the perianth (usually more or less perigynous), free or connate; gynoecium (2-)3 carpelled, syncarpous, styles 2-3, free to partially jointed, apical, stigmas 2-3, ovary superior, unilocular, uniovulate, placentation basal, orthotropous. Fruit dry, indehiscent usually a trigonous or flattened nut or achene-like, sometimes enclosed by a fleshy hypanthium or perianth, 1 seeded. Seeds with ruminate (Coccoloba P. Browne) or not-ruminate endosperm, oily, starchy, cotyledons 2, embryo straight to curved.

 

Notes on delimitation

  • Traditionally the Polygonaceae were placed within the Caryophyllales on the basis of the unilocular ovary and single, basal ovule. However, recent studies have revealed that the family lacks the P-type sieve-tube plastids, anatropous ovules, betalain pigments and perisperm characters that characterise the order Caryophyllales. Recent studies by the APG II (2003) still include the Polygonaceae within the Caryophyllales.

Distribution in the Neotropics

  • The Polygonaceae are cosmopolitan, with most genera and species occurring in northern temperate regions. 31 genera are found in the western hemisphere. 16 of these genera are restricted to western North America, with 3 disjunct to Chile and Argentina.

Of the 13 tropical and subtropical American genera:

  • Ruprechtia C.A.Mey., Triplaris Loefl., and Coccoloba P.Browne are fairly widespread in the Neotropics;
  • Neomillspaughia S.F.Blake, Podopterus Kunth, Gymnopodium Rolfe and Antigonon Endl. are restricted to Central America.
  • The monotypic Leptogonum Benth. is endemic to Hispaniola.
  • Symmeria Benth. is amphiatlantic.
  • Muehlenbeckia Meisn. is amphipacific.
  • Polygonum L., Rumex L., and Persicaria L. are cosmopolitan.

Distinguishing characters (always present)

  • Stems often with conspicuous swollen nodes.
  • Stipules present.
  • Ochreas are present in the Polygonoideae, absent in the Eriogonoideae (this subfamily is not represented in the Neotropics).

Other important characters

  • Flowers small, often unisexual (Coccoloba), sometimes with attractive bracts (Antigonon). Fruits with accrescent calyx (Triplaris).

Key differences from similar families

  • Polygonaceae are characterised by the presence of the ochrea (absent from subfam. Eriogonoideae), and have leaves spirally alternate, swollen nodes and involucred inflorescence. Vegetatively they can be confused with Piperaceae (swollen nodes, leaves with irregular base) but they have a deciduous terminal stipule and very small flowers densely arranged in spikes.

Number of genera

  • Antigonon (6 species).
  • Coccoloba (120 species).
  • Gymnopodium (3 species).
  • Leptogonum (one species endemic to Hispaniola).
  • Muehlenbeckia (9 species).
  • Neomillspaughia (2 species).
  • Persicaria (c. 5 species).
  • Podopterus (3 species).
  • Polygonum (c. 30 species).
  • Rumex (c. 15 species).
  • Ruprechtia (37 species).
  • Symmeria (1 species).
  • Triplaris (18 species).

Useful tips for generic identification

See below.

Notable genera and distinguishing features

  • Coccoloba - erect or climbing woody plants, unisexual flowers and pedunculate fleshy fruits.
  • Ruprechtia - trees to shrubs, three-winged fruits, female partial inflorescences 2-3-flowered, male flowers pedicellate, twigs often solid.
  • Triplaris - shrubs to trees, three-winged fruits, female partial inflorescences 1-flowered, male flowers sessile, often associated with ants that live in its hollow branches.
  • Polygonum - erect herbs with flowers in spikes, closely allied to Persicaria.
  • Antigonon - climbing plants with showy bracts protecting inflorescences.

 

Status

  • While Coccoloba, Ruprechtia and Triplaris are endemic to the Neotropics, Rumex, Polygonum and Antigonon have weedy status, with species of knot-weed (Polygonum) being particularly invasive in Europe.
  • Antigonon leptopus Hook. & Arn. originates from Mexico but is cultivated worldwide because of its showy flowers. Buckwheat, used in Japan for making pasta (soba, Fagopyrum esculentum Moench) is an increasingly popular, gluten-free alternative to wheat.

 

Important literature

APG II, 2003. An update of the Angiosperm Phylogeny group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141(4): 399-436.

BRANDBYGE, J. 1986. A revision of the genus Triplaris (Polygonaceae). Nord. Journ. Bot. 6(5).

BRANDBYGE, J. 1989. Polygonaceae. Flora of Ecuador. 38:39.

BUCHINGER, M. & SANCHEZ, E. 1959. Sinopsis preliminar de las especies argentinas del genero Coccoloba. Bol. Soc. Arg. Botanica, v.7, n.3/4, p.251-255.

BURGER, W. 1983. Polygonaceae. In: Burger. Flora Costaricensis. Fieldiana Botany. Field Museum of Natural History, n.s. 13, p.99-138.

CIALDELLA, A. M. 1989. Revisión de las espécies argentinas de Polygonum s.l. (Polygonaceae). Darwiniana 29(1-4):179-246.

CIALDELLA, A.M. 2001. Polygonaceae. In Spichiger & Ramella. Flora del Paraguay v. 33: 1-106.

HOWARD, R. A. 1960. Polygonaceae. In: Woodson (ed.). Flora of Panama. Annals of the Missouri Botanical Garden, 47: 340-357.

HOWARD, R. A. 1961. Studies in the Genus Coccoloba, X. New species and a summary of distribution in South America. Journ. Arn. Arb. 42(1): 87-95.

HOWARD, R. A. 1992. Collected notes on Coccoloba L. (Polygonaceae). Brittonia 44: 356-367.

MARTÍNEZ, R. V. 1997. Polygonaceae. In: Lleras & Taylor. Flórula de las reservas biologicas de Iquitos. Peru. Missouri Botanical Garden. Press. p.587-592.

MELO, E. 1996. Levantamento das espécies de Coccoloba (Polygonaceae) da restinga do estado da Bahia, Brasil. Sitientibus 15:49-59.

MELO, E. 1998. Levantamento da família Polygonaceae no estado da Bahia, Brasil: espécies do semi-árido. Rodriguesia 50(76/77):19-37.

MELO, E. 2000. Polygonaceae da Cadeia do Espinhaço, Brasil. Acta Bot. Bras. 14(3):273-300.

MELO, E. & F. FRANÇA. 2006. A familia Polygonaceae no semi-árido brasileiro. In A.M. Giulietti et al. (eds) Diversidade e Caracterização das fanerógamas do semi-árido brasileiro. In A. Giulietti  & L. Queiroz Instituto do Milênio do Semi-Árido, v. 1, p. 437-488.

PENDRY, C.A. 2004. Monograph of Ruprechtia (Polygonaceae). Systematic Botany Monographs 67: 1 - 113.

How to cite

Melo, E. & França, F. (2009). Neotropical Polygonaceae. 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/Polygonaceae.htm.