Oxalidaceae R.Br.

Oxalidaceae, A. W. Exell. Flora Zambesiaca 2:1. 1963

Morphology General Habit

Annual or perennial herbs, rarely trees or shrubs or shrublets

Morphology Leaves

Leaves alternate, exstipulate (but sometimes with stipule-like expansions at the base of the petiole), digitately or pinnately 1-? -foliolate

Morphology Reproductive morphology Flowers

Flowers in axillary cymes or in pseudumbels or solitary, actinomorphic or nearly so, bisexual, 5-merous, often heterostylous, sometimes cleistogamous and reduced

Morphology Reproductive morphology Flowers Calyx

Sepals 5, free, imbricate (rarely valvate)

Morphology Reproductive morphology Flowers Corolla

Petals 5, contorted or imbricate, free or slightly connate at the base

Morphology Reproductive morphology Flowers Androecium

Stamens 10 (15), 2 (3)-seriate; anthers versatile, 2-thecous; filaments ± connate at the base

Morphology Reproductive morphology Flowers Gynoecium

Ovary superior, 5-locular; loculi 1-?-ovulate, with axile placentation; styles 5 (rarely 1), free; stigmas capitate, entire

Morphology Reproductive morphology Fruits

Fruit a loculicidally dehiscent capsule (rarely baccate)

Morphology Reproductive morphology Seeds

Endosperm fleshy or absent

Fiaschi, P. (2010). Neotropical Oxalidaceae.

Morphology

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.

Distribution

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.

Diagnostic

Notable genera and distinguishing features

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

Distinguishing characters (always present)

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

General Description

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.
• Oxaliscorniculata 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).

Number of genera

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

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.

Literature

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.

Oxalidaceae, Hutchinson and Dalziel. Flora of West Tropical Africa 1:1. 1954

Morphology General Habit

Herbaceous or suffrutescent, rarely arborescent

Morphology Leaves

Leaves alternate, digitately or pinnately compound, sometimes simple by suppression of the leaflets; leaflets spirally coiled when young, usually closing at night; stipules absent

Morphology Reproductive morphology Flowers

Flowers hermaphrodite, actinomorphic, sometimes of two kinds, some perfect and others minute and apetalous, solitary or subumbellate, rarely racemose or cymose

Morphology Reproductive morphology Flowers Calyx

Calyx 5-fid or 5-partite, imbricate

Morphology Reproductive morphology Flowers Corolla

Petals 5, shortly clawed, free or shortly connate at the base, contorted

Morphology Reproductive morphology Flowers Androecium

Stamens 10, hypogynous, connate at the base, sometimes 5 of them without anthers; anthers 2-celled, opening lengthwise

Morphology Reproductive morphology Flowers Gynoecium

Ovary 5-celled, superior; styles 5, free, persistent; stigmas capitate or shortly divided; ovules 1 or more, axile

Morphology Reproductive morphology Fruits

Fruit mostly a capsule

Morphology Reproductive morphology Seeds

Seeds often with an elastic epidermis; endosperm fleshy, copious; embryo straight