CLEOMACEAE (Cleome Family)

Contributed by David J. Bogler

Plants annual (perennial herbs, shrubs, or trees elsewhere). Leaves alternate, palmately compound or simple. Stipules absent or present, sometimes thornlike. Inflorescences terminal racemes (flowers solitary in the leaf axils elsewhere), the flowers subtended by bracts. Flowers perfect or imperfect, actinomorphic to slightly zygomorphic, hypogynous. Calyx usually with 4 sepals, distinct or fused toward the base. Corolla with 4 to numerous separate petals, these ovate to spatulate, equal or often unequal, usually tapered to a stalklike base. Nectar-producing glands present between the corolla and stamens. Stamens 6 to numerous, usually exserted and showy, equal or unequal but not arranged in clusters of 4 and 2, the filaments slender, the anthers attached at or above the base, dehiscing by longitudinal slits. Pistil usually borne on a short to long, stalklike extension of the receptacle (gynophore) above the calyx, cylindrical, of 2 fused carpels, 1-locular, the placentation parietal. Style 1, often very short and inconspicuous, the stigma capitate or a somewhat concave disk, often shallowly 2-lobed. Fruits capsules, dehiscent by 2 valves, a persistent replum (the thin, placental band of tissue visible as a longitudinal line or nerve around the fruit) often present. Seeds numerous, more or less circular in outline, usually somewhat flattened, appearing folded or curled, with a broadly angled furrow or depression running partway through each face and usually with a small notch where it meets the margin. About 8 genera, 275 species, nearly worldwide.

Until recently, most botanists treated the Cleomaceae as a subfamily of the Capparaceae. Both groups have long been regarded as close relatives of the Brassicaceae, but the phylogenetic relationships between the groups were not well understood. Beginning in the early 1990s, several studies using different sources of data produced similar results, that the largely herbaceous Brassicaceae and Cleomaceae are sister groups and that this assemblage shared a common ancestor with the Capparaceae in the strict sense (Rodman et al., 1993; Judd et al., 1994; Hall et al., 2002). Subsequent authors have wrestled with whether to classify the entire group as one heterogeneous family (Brassicaceae) or to recognize two or three separate families (Hall et al., 2002). What has become apparent is that if Cleome and its relatives are to be combined with some other family, then they must become a subfamily of the Brassicaceae, not the Capparaceae.

Morphologically and phytochemically, the Brassicaceae in the restricted sense are a relatively easily recognized group distinguished by the presence of mustard oils, specialized capsular fruits with valves separating from persistent placenta tissues (replum) often divided by a false septum, six stamens positioned in groups of four and two (tetradynamous), and a folded embryo (Judd et al., 1994). Capparaceae and Cleomaceae have some of these features as well, but they have six or more nontetradynamous stamens. Capparaceae in the strict sense are usually trees or shrubs and have fruits that are berries or capsules lacking a replum. The mostly herbaceous Cleomaceae have capsules with a replum but lacking a false septum. The present treatment deviates from that of Cronquist (1981, 1991) in recognizing the Cleomaceae as a distinct family. This seems the most pragmatic solution to the problem, one that is phylogenetically sound while preserving two morphologically distinct groups in the Missouri flora. The true Capparaceae, comprising about 25 genera and 440 species, are not represented in the Missouri flora, other than by the edible pickled flower buds of the Mediterranean Capparis spinosa L. (capers) included by gourmet chefs in some tasty dishes.