1. Polygala L. (milkwort)

Plants annual or perennial herbs (shrubs elsewhere). Stems unbranched or branched, in our species glabrous or inconspicuously hairy. Leaves alternate or less commonly opposite or whorled (sometimes appearing leafless or nearly so at flowering in P. incarnata), sessile or very short-petiolate, the lowermost leaves sometimes reduced and scalelike. Stipules absent. Leaf blades simple, unlobed, variously shaped, the margins entire or minutely toothed, glabrous (variously hairy elsewhere). Inflorescences terminal, often spikelike racemes, the flowers usually short-stalked, subtended by small, inconspicuous, membranous to scalelike bracts. Flowers hypogynous, perfect. Calyces zygomorphic, of 5 sepals, these free, the upper sepal and the lower pair small and green or whitish green, the lateral pair (referred to as wings) larger and petaloid. Corollas zygomorphic, of 3 petals, these usually fused into a U-shaped tube open along 1 side, the upper (appearing lateral) 2 lobes similar, the lower (appearing central) lobe (referred to as a keel) boat-shaped, often fringed or crested on the outer surface (or mainly at the tip), greenish white to white, pink, or pinkish purple (other colors elsewhere). Stamens 8 (6 elsewhere), the filaments fused into a tube just inside the keel that is split longitudinally along the upper side, also fused to the corolla tube, the anthers attached at their bases, usually yellow, the pollen usually shed by apical pores or short slits. Pistil 1 per flower, of 2 fused carpels. Ovary superior, 2-locular, often flattened, the placentation axile (appearing more or less apical). Style 1, often curved toward the tip, usually unequally 2-lobed near the tip, the upper lobe bearing a more or less capitate stigma, the other lobe sterile, with a fringe of hairs. Ovule 1 per locule. Fruits capsules, variously shaped, dehiscing longitudinally. Seeds oblong-obovoid to obovoid, the surface dark brown to black, moderately to densely pubescent with loosely appressed to more or less spreading, fine, straight hairs, also with a white or yellowish aril at the attachment point. About 325 species, nearly worldwide.

The estimate of number of species in Polygala cited above is based on the traditional broad circumscription of the genus. However, molecular data have suggested that the genus is actually an artificial assemblage of several groups more closely related to other genera than to Polygala in the strict sense (Persson, 2001). Abbott (2011) has recently advocated for the recognition of four segregate genera in the New World, based on preliminary molecular data and morphological analysis. In Abbott’s restricted sense, Polygala worldwide contains only about 200 species. However, all of the Missouri species remain within Polygala, even in the strict sense.

Some species of Polygala are cultivated as ornamentals. The Missouri species tend not to produce cleistogamous flowers, but elsewhere a number of species produce cleistogamous flowers, including some that produce them on subterranean branches.