My concept of subsp. setosa is embodied primarily in those viscid multifoliolate Setosae in which these characters coincide: a triple pubescence of plain setae, glandular setulae and villi, but no prickles; thin-textured veinless or dorsally faintly costate leaflets spaced to 1-2.5 mm apart along rachis; an externally glabrous pappiform calyx; corolla lobes charged dorsally with a few subsessile or short-stalked glands intermixed with plain setulae; and a relatively thin-walled, piano-compressed pod of which the villosulous and thinly setose valves break irregularly or incompletely into articles wider than long. On this general theme occurs considerable variation in mutual proportions of the three types of trichome, and a number of populations do not answer perfectly to all the ideal morphological conditions. Further, the floral bracts vary from about two- thirds as long to fully as long as the expanded bisexual corollas, the capitulum consequently varying prior to anthesis from conelike to moriform.
Around the nucleus of exactly or nearly typical subsp. setosa, which is most common and most clearly differentiated in southern Goiás and Distrito Federal, are clustered several forms in one way or another departing from the idealized formula of the subspecies. In north-central São Paulo the pod, elsewhere sessile or almost so, becomes markedly stipitate, and interpinnal spicules are lacking from the leaf-stalk. This form was known to Bentham, but referred to the related
M. melanocarpa, always distinguished by an externally silky-setose calyx; it is described below as var. pseudomelas. Locally in western Minas Gerais the calyx is reduced, quite or nearly, to the tube, as in subsp. paludosa, and both plain and gland-tipped setae disappear simultaneously from stem and leaf-stalk; this corresponds to var. nitens Benth. An anomalous form that retains the pappiform calyx of subsp. setosa but has lost all glandular pubescence below the pod is here described from central Minas Gerais as var. rupigena.