From The Plant Encyclopedia
Cleome is a genus of flowering plants in the family Cleomaceae. Previously it had been placed in family Capparaceae, until DNA studies found the Cleomaceae genera to be more closely related to Brassicaceae than Capparaceae. The APG II system<ref name=apg>Stevens, P. F. (2001 onwards) Angiosperm Phylogeny Website: Brassicales.</ref> allows for Cleome and the other members of Cleomaceae to be included in Brassicaceae.
The genus sensu stricto includes about 170 species of herbaceous annual or perennial plants and shrubs.<ref name=huxley>Huxley, A., ed. (1992). New RHS Dictionary of Gardening 1: 652-653. Macmillan ISBN 1-56159-001-0.</ref> The genus has a subcosmopolitan distribution throughout the tropical and warm temperate regions of the world.<ref name=huxley/> However a recent DNA study failed to separate Cleome, Podandrogyne and Polanisia from each other, so some taxonomists have abandoned the last two of these genera, treating them as part of Cleome sensu lato; in this case Cleome contains about 275 species, the vast majority of the Cleomaceae.
As a genus it contains species which show a developmental progression from C3 photosynthesis to C4 photosynthesis. This combined with its being a Brassicaceae (and therefore closely related to the model plant species Arabidopsis thaliana) make it an ideal genus in which to study how C4 photosynthesis occurs and how it evolved. Morphological differences that demonstrate the transition from C3 to C4 include C3 species having more veins and larger bundle sheath cells. There are also proteins present in species such as Cleome gynandra which are needed for C4 photosynthesis.<ref>Marshall, D.M., Muhaidat, R., Brown, N.J., Liu, Z., Stanley, S., Griffiths, H.G., Sage, R.F., Hibberd, J.M. (2007) Cleome, a genus closely related to Arabidopsis, contains species spanning a developmental progression from C3 to C4 photosynthesis. Plant Journal, 51: 886-896 </ref>
Sources:<ref name=grin2>Germplasm Resources Information Network: Cleome list</ref><ref name=huxley/><ref name=fleur>Flora Europaea: Cleome list</ref><ref name=usda>USDA Plants Profile: Cleome list</ref><ref name=efloras>Efloras: Cleome search results</ref>
Cultivation and uses
Cleome hassleriana (spider flower) is a commonly cultivated garden plant, which can become invasive if attention is not paid to removing it before it can shed its seeds.