**Oxalis pes-caprae L. (Oxalidaceae)**

**Bermuda Buttercup**

**Description**. Perennial, somewhat succulent; stems 10-20 cm long,
erect but subterranean, fleshy, producing white to light brown bulbs
near the base and above the roots. Leaves in a basal rosette, compound,
petiolate, with 3 leaflets, leaflets 10-30 mm mm long, green, often
spotted, usually obcordate, folding lengthwise at night. Flowers 3-20,
bisexual, radial, in an umbel, the peduncle 10-30 cm long. Sepals 5,
distinct, lanceolate to oblong, petals 5, 15-25 mm long, somewhat united
at the base, yellow, stamens 10, in two sets, five long and 5 short, the
filaments pilose; ovary superior, with 5 locules, 5 style branches. In
California flowering from February to May, but not producing seeds
(plants in California apparently sterile). (Munz 1959, Ornduff 1993,
Valentine 1968, Webb et al 1988).

Synonym= *Oxalis cernua* Thunberg.

**Geographic** **distribution**. A native of southern Africa, Bermuda
buttercup has become naturalized in Great Britain, Mediterranean Europe,
California, Chile, Australia, and New Zealand. (Chapman 1991, Galil
1968, Michael 1964, Munz 1959, Ornuduff 1987, Valentine 1968, Webb et al
1988).

Bermuda buttercup was first reported (as *O. cernua*) in the early 20th
century as a weed in orchards (Robbins 1940). It has been reported from
Santa Cruz Island (Junak et al. 1997) and occurs throughout most
California coastal counties (Anonymous 1998, Ornduff 1993).

**Reproductive and vegetative biology**. *Oxalis pes-caprae* is
heterostylous and self-incompatible (Ornduff 1974, 1987). Populations in
South Africa are tristylous (composed of three different floral forms
with style and stamen lengths corresponding to 3 different levels).
Sexual populations are either diploid or tetraploid, but a sterile,
pentaploid race is believed derived from diploid X tetraploid hybrids.
Although sexual plants can be weedy, the sterile pentaploid is
apparently the only race that has become widespread outside of South
Africa (Michael 1964, 1965, Ornduff 1987), spreading entirely by
bulblets formed at the base of the succulent stem (Galil 1968, Peirce
1973, Putz 1994).

Seeds of the diploid and tetraploid forms require a light stimulus for
germination, which is enhanced by warm, moist conditions and require
light (Marshall 1987, Peirce 1973). The primary mode of reproduction,
however, are bulbs produced by subterranean stems.

In the presence of spring rains, bulbs of the sterile pentaploid produce
roots and young shoots within 4 to 6 weeks (Lane 1984). Each bulb
develops two different subterranean stem systems, one vertical, the
other horizontal (Galil 1968). The vertical stem gives rise to the
aerial shoot system and may also produce axillary buds that develop into
bulbs. The horizontal stem grows laterally by means of contractile
roots. At maturity the horizontal stem becomes a storage organ (water,
nutrients) and develops a terminal bulb immediately above the roots.
Both kinds of stems can develop adventitious roots (Galil 1968),
especially if damaged or cut by disturbance (e.g., plowing, digging).
Mature plants may produce up to 20 bulblets, most of which are dispersed
from the parent plant at the end growing season (Galil 1964, 1968, Putz
1994). Bulbs are sensitive to freezing, but can persist for more than 3
years in a vegetative condition if kept dry (Marshall 1987). Cultivation
and redistribution of soils are the most prevalent means of bulb
dispersal (Galil 1968, Paspatis 1985), but birds and and mole rats (in
South Africa) also disperse the bulbs (Galil 1967, Young 1958).

Bermuda buttercup has been found to be toxic to livestock (Rekhis 1994).

**Ecological distribution.** Bermuda buttercup occurs in cultivated and
fallow fields, irrigation ditches, along roadsides, and open sites
(Galil 1968, Hildreth and Agamalian 1985, Munz 1959, Ornduff 1993).

**Weed status.** *Oxalis pes-caprae* is not considered a serious weed 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 not listed
for the United States in Lorenzi and Jeffery (1987).

**Microbial pathogens**. No literature was found that reported microbial
pathogens of *Oxalis pes-caprae*.

**Insect pathogens**. The noctuid moth, *Klugeana philoxalis*,
selectively feeds on bermuda buttercup and has been recommended as a
biocontrol in South Africa (Kluge and Claasens 1990).

**Herbicide** **control**. Hildreth and Agamalian (1985) recommended the
use of oxyflourflen in California artichoke fields. The most effective
long-term treatment was found to be associated with initial appearnace
of shoots from single bulbs. Other herbicide treatments, including 2,4-D
and glyphosate, have been evaluated but their use was inneffective at
levels considered to be safe for cultivated grapes and other perennial
crops (Marshall 1987, Michael 1965, Paspatis 1985).

**Other control methods**. Bermuda buttercup is a host to broomrape
(*Orobanche* sp.), which selectively infests herbaceous plants in Greek
vineyards (Paspatis 1985).

**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.

Chapman, A. 1991. Australian plant name index. K-P. Australian
Government Publishing Service, Canberra. pp. 1711-2495.

Galil, J. 1967. On the dispersal of the bulbs of *Oxalis cernua* Thung.
by mole-rats (*Spalax ehrenbergi* Nehrin). Journal of Ecology 55:
787-792.

Galil, J. 1968. Vegetative dispersal in *Oxalis cernua*. American
Journal of Botany 55: 68- 73.

Hildreth, R. and H. Agamalian. 1985. Control of buttercup oxalis in
artichokes with oxyfluorfen. Proceedings, Western Society of Weed
Science. 38: 187-195.

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.

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.

Kluge, R. and M. Claasens. 1990. *Klugeana philoxalis* Geertsema
(Noctuidae: Cuculliinae), the first potential biological control agent
for the weed *Oxalis pes-caprae* L. Journal of the Entomological Society
of Southern Africa. 53: 191-198.

Lane, D. 1984. Factors affecting the development of of populations of
*Oxalis pes-caprae* L. Weed Research 24: 219-225.

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

Marshall, G. 1987. A review of the biology and control of selected weed
species in the genus *Oxalis*: *O. stricta* L., *O. latifolia* H.B.K.
and *O. pes-caprae* L. Crop Protection. 6: 355-364.

Michael, P. 1964. The identity and origin of varieties of *Oxalis
pes-caprae* L. naturalized in Australia. Transactions, Royal Society of
South Australia. 88: 167-173.

Michael, P. 1965. Studies on *Oxalis pes-caprae* L. in Australia. The
control of the pentaploid variety. Weed Research 5: 133-140.

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

Ornduff, R. 1974. Heterostyly in South African plants: a conspectus.
Journal of South African Botany. 1: 1-355.

Ornduff, R. 1987. Reproductive systems and chromosome races of *Oxalis
pes-caprae* L. and their bearing on the genesis of a noxious weed.
Annals of the Missouri Botanical Garden. 74: 79-84.

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.

Paspatis, E. 1985. Chemical, cultural and biological control of *Oxalis*
*pes-caprae* in vineyards in Greece. pp. 27-29. In R. Cavalloro and D.
Robinson. (eds). Weed control on vine and soft fruits. Dublin, Ireland.

Peirce, J. 1973. Soursob (*Oxalis pes-caprae* L.) in Western Australia
its life history, distribution, morphological variation and weed
potential. Western Australia, Dept. of Agriculture. Technical Bulletin
20. 9 pp.

Putz, N. 1994. Vegetative spreading of *Oxalis pes-caprae*
(Oxalidaceae). Plant Systematics and Evolution. 191: 57-67.

Rekhis, J. 1994. The poisonous plant *Oxalis cernua*. Veterinary and
Human Toxicology. 36: 23.

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

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.

Webb, C., W. Sykes, and P. Garnock-Jones. 1988. Flora of New Zealand.
Volume 4. Naturalized pteridophytes, gymnosperms, dicotyledons.
Department of Scientific and Industrial Research, Christchurch. 1365 pp.