Oxalis corniculata L.

Etymology Genus
Sour, because of the presence of oxalis acid
Species Small horns, likely in reference to the upward pointing fruits
Synonyms -
Common Names Yellow Wood Sorrel, Sleeping Beauty, Creeping Wood Sorrel
Status Exotic: Naturalised
Form Herbaceous creeper
Native Distribution Obscure

Diagnostic: Oxalis corniculata trifoliate leaves that are each heart-shaped. Another similar-looking and very common trifoliate weed of managed turf is Desmodium triflorum. However, the latter only have a slight notch at the tip of the leaflet and each leaflet is arranged 90° from each other at the midrib (O. corniculata's leaflets are aligned almost at 120°).

Interesting Facts: This creeper is a very common weed on manicured grassland. The fruit resembles a small Lady's Finger but its dispersal is facilitated by explosive mechanism. After the inner fruit walls dried out, a light touch to it can cause the fruit to split and release its reddish-brown seeds. Foo (2002) suggested that the seeds may be dispersed further by adhering to animals through its rough coating.

The Yellow Wood Sorrel's obscure origin is likely to be due to its wide-spread naturalisation (GRIN, 1995).

Oxalis corniculata
The form of the Yellow Wood Sorrel, showing its heart-shaped trifoliate leaves and the flower.
 
Oxalis corniculata   Oxalis corniculata
The yellow flowers are very small relative to the leaves
Fruit before (left) and after splitting (right). Note the reddish seeds left over.    

References

GRIN (1995) Taxon: Oxalis corniculata L. Germplasm Resources Information Network. United States Department of Agriculture. http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?26196. Accessed on 10-Dec-2012.

Foo TS. (2002) A Guide to the Wildflowers of Singapore. Singapore Science Centre, Singapore. 160 pp.

 
Posted on 9-Dec-2012 / Last Updated on 11-Jan-2015
Family: Oxalidaceae