The Cleomaceae are a small family of flowering plants in the order Brassicales, comprising about 220 species in two genera, Cleome and Cleomella.[2] These genera were previously included in the family Capparaceae, but were raised to a distinct family when DNA evidence suggested the genera included in it are more closely related to the Brassicaceae than they are to the Capparaceae. The APG II system allows for Cleomaceae to be included in Brassicaceae.[3] Cleomaceae includes C3, C3–C4, and C4 photosynthesis species.[4]
In 1994, a group of scientists including Walter Stephen Judd suggested to merge the Capparaceae (which at that time included the Cleomaceae) with the Brassicaceae. Early DNA-analysis showed that the Capparaceae - as defined at that moment - were paraphyletic, and others suggested to assign the genera closest to the Brassicaceae to the Cleomaceae.[5] The Cleomaceae and Brassicaceae diverged approximately 41 million years ago.[6] All three families have consistently been placed in one order (variably called Capparales or Brassicales).[5] The APG II system merged Cleomaceae and Brassicaceae. Other classifications have continued to recognise the Capparaceae, but with a more restricted circumscription, either including Cleome and its relatives in the Brassicaceae or recognizing them in the segregate family Cleomaceae. The APG III system has recently adopted this last solution, but this may change as a consensus arises on this point. Current insights in the relationships of the Brassicaceae, based on a 2012 DNA-analysis, are summarized in the following tree.[7]
Two genera are currently accepted, Cleome with 199 species, and Cleomella with 22 species. Plants of the World Online considers Oxystylis, Peritoma, and Wislizenia synonyms of Cleomella.[2]
Cleomaceae are mostly annual, sometimes perennial herbaceous plants, seldom shrubs or small trees, and some are lianas. Most of them have glands, a character setting them apart from the related Capparaceae, and contain resins, and may have an aromatic or foetid smell. The alternately set leaves, have stalks and never form a sheath around the stem. The leaves are always palmately compound, mostly with three to seven leaflets, rarely with just one leaflet. At the base of the leafstalk sit scaly, leafy or spiny stipules, a difference with its sister group Brassicaceae that consistently lack stipules, although a pair of glands can sometimes be present at the base of the leaf stalk. Hairs and papillae may be present.[8]