**Oxalis corniculata (Oxalidaceae)**

**Creeping Wood-Sorrel**

**Description**. Perennial, from a slender taproot; stems 5-50 cm long,
prostrate to procumbent, rooting at the nodes, glabrous to puberulent,
the hairs appressed to spreading. Leaves stipulate, in clusters at the
nodes, erect, compound, petiolate, with 3 leaflets, leaflets 5-20 mm
long, often purplish, usually obcordate, folding lengthwise at night.
Flowers 1-7, in umbellate clusters, radial, bisexual, sepals 5,
distinct, petals 5, 4-8 mm long, somewhat united at the base, yellow,
stamens 10, in two sets, five long and 5 short; ovary superior, with 5
locules, 5 style branches; fruit a capsule, dehiscing longitudinally;
seeds reddish brown, reticulate to ridged. In California, flowering from
May to November. (Gleason and Cronquist 1991, McGregor 1986, Munz 1959,
Valentine 1968, Welsh et al. 1987)

Synonym = *Oxalis repens* Thunb.

**Note:** *Oxalis corniculata* sometimes has been confused in California
with the native *Oxalis* *albicans*, which has green leaves, petals 8-12
mm long, and which lacks stoloniferous stems. Elsewhere it has been
confused with *O. stricta* L. (Eiten 1963). Apparently var. *repens*
(Thunb.) Zucc., a native of southern Africa, represents the race that
has become established elsewhere as a weed in the world, including
Europe. (Arnold and de Wet 1993, Valentine 1968)

**Geographic distribution**. Generally believed to be a native of
Eurasia, creeping wood sorrel (as both var. *corniculata* and var.
*repens*) is widespread in North America, South America, Africa,
Australia, Asia and New Zealand (Arnold and de Wet 1993, Chapman 1991,
Holm et al. 1977, Gleason and Cronquist 1991, Ornduff 1993, Watson 1989,
Webb et al. 1988, Valentine 1968, Welsh 1987).

It ws first reported from near San Francisco by Bolander (1870) and
southern California (Brewer et al. 1876), but also had been collected
during the 1840s (Howell 1937). By the late 19th century it had become
widely established in southern California (Hilgard 1890, Robbins 1940).
It has been reported from Santa Cruz and Santa Rosa islands (Junak et al
1997), and is widespread throughout much of California west of the
Sierra Nevada (Anonymous 1998, Ornduff 1993).

**Reproductive and vegetative biology**. Natural populations of *Oxalis*
*corniculata*, unlike most other members of the genus, is heterostylous
(with 3 floral forms) but self-compatible and strongly self-pollinating
(Lovett Doust et al. 1981, Ornduff 1972). However, greenhouse
populations and presumably other naturalized populations may be
homomorphic, self-compatible, and largely self-pollinating (Lovett Doust
et al. 1985, Shibaike et al. 1996). Shibaike et al. (1996) found
considerable variation among local naturalized populations in Japan for
morph ratios and levels of self-pollination.

It flowers throughout the year in warm temperate or tropical climates.
At fruting maturity, capsules dehisce explosively, so that seeds are
dispersed several cm from the source (Robertson 1975). Seeds have no
dormancy and may germinate within 2 weeks after dispersal, but the level
of germination is dependent primarily on soil temperature (Holt 1987).
Seeds produced during winter months generally germinate at 15° to 25° C,
whereas seeds produced during the summer months germinate at 10° to 30°
C. Warcup (1980) reported that heat treatments also stimulated
germination. Seeds retained under dry conditions at room temperature
retained high levels of viability and germinability for over 1 year
(Holt 1987).

**Ecological distribution.** Creeping wood-sorrel has been reported from
disturbed open sites, roadsides, gardens, lawns, greenhouses, cultivated
fields, and waste areas (Gleason and Cronquist 1991, Lourteig 1979,
McGregor 1986, Munz 1959, Valentine 1968, Welsh et al. 1987).

**Weed status.** *Oxalis corniculata* is considered one of the most
serious and noxious weeds in agricultural or horticultural practice, at
least at a global level (not listed by Holm et al. 1977), nor is it
considered a noxious weed by the State Dept. of Food and Agriculture
(Anonymous 1996). It is listed (presumably under the name *O. stricta*)
for the United States by Lorenzi and Jeffery (1987). In most temperate
climates, *Oxalis corniculata* is primarily considered a lawn, garden,
greenhouse, and container-plant weed rather than one infesting
cultivated fields and natural plant communities (Lovett Doust et al.
1985, Lorenzi and Jeffery 1987, Lourteig 1979).

**Microbial pathogens**. Creeping wood-sorrel has been reported to be a
host of the rust, *Puccinia bakshii* (De 1997).

**Insect pathogens.** Creeping wood-sorrel has been reported as an
alternate host of nematodes (Holm et al. 1977).

**Herbicide control**. Several herbicides have been used in the control
of creeping wood-sorrel, including aciflouren, atrazine, chloramben,
chlorimuron, dicamba, 2,4-D, imazaquin, oxyflourfen, and trichlopyr
(Colvin and Rice 1987, Elmore 1984, Holt and Chism 1988, Lorenzi and
Jeffery 1987, Moore et al. 1989). Moore et al. (1989) reported complete
control of seed germination using imazaquin and oxyflourfen with
container plants.

**Literature Cited**

Anonymous. 1996. Exotic pest plants of greatest ecological concern in
California as of August 1996. California Exotic Pest Plant Council. 8
pp.

Anonymous. 1998. California county flora database version 2, Santa
Barbara Botanic Garden and USDA National Plants Data Center, Santa
Barbara and New Orleans. URL = plants.usda.gov

Arnold, T. and B. de Wet. 1993. Memoir 62. Plants of southern Africa:
names and distribution. National Botanical Institute, Pretoria. 825 pp.

Bolander, H. 1870. A catalog of plants growing in the vicinity of San
Francisco. A. Roman and Co., San Francisco, California. 43 pp.

Brewer, W., S. Watson, and A. Gray. 1876. Geological Survey of
California. Volume 1. John Wilson, University Press, Cambridge,
Massachusetts. 622 pp.

Colvin, S. and R. Rice. 1987. Selective post-emergence control of
*Oxalis corniculata* in *Cymbidium hybrida*. Journal of Environmental
Horticulture. 5: 141-142.

De, A. 1997. A new species of *Puccinia* from India. Mycotaxon. 62:
337-340.

Eiten, G. 1963. Taxonomny and regional variation of *Oxalis* section
*Corniculatae*. I. Introduction, keys and synopsis of the species.
American Midland Naturalist. 69: 257-309.

Elmore, C. 1984. Control of *Oxalis corniculata,* creeping woodsorrel,
in cool season grass turf. Proceedings, Western Society of Weed Science.
37: 158-159.

Gleason, H. and A. Cronquist. 1991. Manual of the vascular plants of
northeastern United States and Adjacent Canada. 2nd edition. New York
Botanic Garden, Bronx. 910 pp.

Hilgard, E. 1890. The weeds of California. California Agricultural
Experiment Station Report. pp. 238-252.

Holm, L., D. Plucknett, J. Pancho, and J. Herberger. 1977. The world's
worst weeds: distribution and ecology. University Press of Hawaii,
Honolulu. 609 pp.

Holt, J. 1987. Factors affecting germination in greenhouse-produced
seeds of *Oxalis corniculata*, a perennial weed. American Journal of
Botany. 74: 429-436.

Holt, J. and J. Chism. 1988. Herbicidal activity of NAA
(1-naphthaleneacetic acid) on creeping woodsorrel (*Oxalis corniculata*)
in ornamentals. Weed Science. 36: 227-233.

Howell, J. 1937. A Russian collection of California plants. Leaflets of
Western Botany 2: 17-20.

Junak, S., S. Chaney, R. Philbrick, and R. Clark. 1997. A checklist of
vascular plants of Channel Islands National Park. Southwest Parks and
Monuments Association, Tucson, AZ. 43 pp.

Lorenzi, H. and L. Jeffery. 1987. Weeds of the United States and their
control. Van Nostrand Company, New York. 355 pp.

Lourteig, A. 1979. Oxalidaceae - extraaustroamericanae. II. *Oxalis*,
section *Corniculatae*. Phytologia 42: 57-199.

Lovett Doust, L. J. Lovett Doust, and P. Cavers. 1981. Fewrtility
relationships in closely related taxa of *Oxalis*, section
*Corniculatae*. Canadian Journal of Botany 59: 2603- 2609.

Lovett Doust, L., A. MacKinnon, and J. Lovett Doust. 1985. Biology of
Canadian weeds. 71. *Oxalis stricta* L., *Oxalis corniculata* L.,
*Oxalis dillenii* Jacq. ssp. *dillenii* and *Oxalis dillenii* Jacq. ssp.
*filipes* (Small) Eiten. Canadian Journal of Plant Science. 65: 691-
709.

McGregor, R. 1986. Oxalidaceae. pp. 578-579. In Great Plains Flora
Association. Flora of the Great Plains. University of Kansas, Lawrence.
1392 pp.

Moore, B., R. Larson, and W. Skroch. 1989. Herbicide treatment of
container-grown \'Gloria\' azaleas and \'Merritt Supreme\' hydrangeas.
Journal of the American Society for Horticultural Science. 114: 73-77.

Munz, P. 1959. A flora of California. University of California Press,
Berkeley. 1681 pp.

Ornduff, R. 1972. The breakdown of trimorphic compatibility in *Oxalis*,
section *Corniculatae*. Evolution 26: 52-65.

Ornduff, R. 1993. Oxalidaceae. pp. 808-809. In Hickman, J. (ed.). The
Jepson manual: Vascular plants of California. University of California
Press, Berkeley. 1400 pp.

Robbins, W. 1940. Alien plants growing without cultivation in
California. Agricultural Experiment Station. Bulletin 637. University of
California, Berkeley. 128 pp.

Robertson, K. 1975. The Oxalidaceae in the southeastern United States.
Journal Arnold Arboretum 56: 223-239.

Shibaike, H., Y. Ishiguri, and S. Kawano. 1996. Population
differentiation in floral and life history traits of *Oxalis
corniculata* L. (Oxalidaceae) with style length polymorphism. Journal of
Plant Research. 109: 315-325.

Watson, M. 1989. Nomenclatural aspects of *Oxalis* section Corniculatae
in Europe. Botanical Journal of the Linnean Society. 101: 347-362.

Valentine, D. 1968. Oxalidaceae. pp. 192-193. In In Tutin et al. 1968.
Flora Europaea. Volume 2. Rosaceae to Umbelliferae. Camrbidge University
Press, Cambridge. 455 pp.

Warcup, J. 1980. Effect of heat treatment of forest soil on germination
of buried seed. Australian Journal of Botany. 28: 567-572.

Welsh, S., N. Atwood, S. Goodrich, and L. Higgins (eds.). 1987. A Utah
flora. Great Basin Naturalist Memoirs. No. 9: 1-894.