Neotropical Oxalidaceae

Description

Shrubs or herbs with bulb-like tubers, bulbs or fleshy rhizomes. Leaves alternate and spiraled, sometimes forming a basal rosette, usually trifoliolate (sometimes unifoliolate), pinnately or palmately compound, sometimes unifoliolate or reduced and replaced by phyllodes; venation palmate or pinnate, stipules usually lacking. Inflorescences axillary, cymose (sometimes forming an umbel or capitulum), the pedicels articulated. Flowers perfect, hypogynous, radial, pentamerous, sometimes showing trimorphic heterostyly; sepals 5, distinct; petals 5, distinct or very slightly connate, usually convolute, basally clawed, often brightly coloured; stamens 10, basally connate, outer filaments shorter than inner, basis sometimes nectar-producing (or nectar produced in antepetalous glands); anthers longitudinally dehiscent; pollen tricolpate or tricolporate; ovary superior, with 5 free or connate carpels, each locule with (1)2-several ovules, placentation axile; styles 5, distinct; stigmas capitate or punctate, sometimes bilobed. Fruit a loculicidal capsule, often lobed or angled; seeds with a mucilaginous testa, which elastically turns inside out ejecting seeds.

Notes on delimitation

• This family has traditionally been placed close to the Geraniaceae in the order Geraniales. The current placement of the Oxalidaceae is together with the Connaraceae, Cunoniaceae, Elaeocarpaceae and a few smaller families in the order Oxalidales (APG III, 2009). See also 'General notes' below.

Distribution in the Neotropics

• Biophytum DC. - pantropical genus with about 30 neotropical species, in rain forests or disturbed areas from sea level to about 2,000 m alt.
• Oxalis L. - cosmopolitan genus with about 500 spp., approximately 185 of which are found in the Neotropics.

Distinguishing characters (always present)

• Compound (or unifoliolate) leaves.
• Determinate inflorescences.
• Perfect, radial, hypogenous flowers.
• Ten stamens with two different lengths.
• Fruits loculicidal capsules.

Number of genera

• Two native genera (Biophytum and Oxalis) and one inroduced (Averrhoa L.).

Notable genera and distinguishing features

• Biophytum species have imparipinnate leaves clustered at the branch apices, and the terminal leaflet is reduced to a bristle-like mucro.
• Oxalis usually has trifoliolate leaves, either pinnate or palmately arranged.  

Status

• Averrhoa L. has two cultivated species in the Neotropics: A. bilimbi L. and A. carambola L.
• Biophytum DC. has about 30 native and one cultivated species (B. sensitivum) in the Neotropics.
• Oxalis L. has about 185 native species in the Neotropics.
• Oxalis corniculata L. and O. pes-caprae L. are naturalized, and O. tetraphylla (L.) DC. is cultivated.

General notes

• The Tropical Andean genus Hypseocharis L., formerly assigned to Oxalidaceae, has been currently placed in the Geraniaceae.
• Morphological features that support Hypseocharis as part of the Geraniaceae, instead of Oxalidaceae, include the antesepalous position of necariferous glands, presence of 15 stamens in two whorls, adnation of sepal, petal and stamen traces (Devi, 1991), the single style (Judd et al., 2002) and the pollen morphology (Erdtman, 1952).

Important literature

Aymard, G. & Berry, P.E. 2003. Three New Species of Biophytum (Oxalidaceae) from the Venezuelan Guayana. Novon 13 (2): 174-179.

Burger, W. 1991. Flora Costaricensis: Oxalidaceae. Fieldiana, Bot. 28, p. 2-16.

Devi, D.R. 1991. Floral anatomy of Hypseocharis (Oxalidaceae) with a discussion on its systematic position. Pl. Syst. Evol. 177: 161-164.

Erdtman, G. 1952. Pollen morphology and plant taxonomy - angiosperms. Almqvist & Wiksell, Stockholm.

Fiaschi, P. & Conceição, A.A. 2005. Oxalidaceae. In: M.G.L. Wanderley, G.J. Shepherd, T.S. Melhem & A.M. Giulietti (eds) Flora Fanerogâmica do Estado de São Paulo. São Paulo, vol. 4, p. 301-315.

Heibl, C. 2005. Studies on the systematics, evolution, and biogeography of Oxalis sections Caesiae, Carnosae, and Giganteae, endemic to the Atacama Desert of northern Chile. Master thesis. Ludwig-Maximilians-Universität, München.

Judd, W.S., Campbell, C.S., Kellogg, E.A., Stevens, P.F. & Donoghue, M.J. 2002. Plant Systematics: a phylogenetic approach. Sinauer Associates, Sunderland.

Knuth, R. 1930. Oxalidaceae. In: A.G. Engler (ed.) Das Pflanzenreich. Wilheem Englelmann. Leipzig, vol. 6, pt. 130, p. 1-481.

Lourteig, A. 1980. Flora of Panama: Oxalidaceae. Ann. Missouri Bot. Gard. 67: 823-850.

Lourteig, A. 1983. Oxalidáceas. In: R. Reitz (ed.) Flora Ilustrada Catarinense. Herbário Barbosa Rodrigues, Itajaí.

Lourteig, A. 1994. Oxalis L. subgénero Thamnoxys (Endl.) Reiche emend. Lourteig. Bradea 7 (1): 1-197.

Lourteig, A. Oxalis L. subgéneros Monoxalis (Small) Lourt., Oxalis y Trifidus Lourt. Bradea 7 (2): 1-629.

Progel, A. 1877. Oxalidaceae. In: C.F.P. Martius & A.G. Eichler (eds) Flora brasiliensis. Typographia regia, Monarhii, vol. 12, pt. 2, p. 473-519.

How to cite

Fiaschi, P. (2010). Neotropical Oxalidaceae. 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/Oxalidaceae.htm.