Shrubs 0.3–2 (–3) m tall, occasionally described as small trees. Leaves decussate; petiole eglandular; lamina eglandular or bearing 1–5 small cylindrical glands on margin on each side of proximal half; stipules lacking or interpetiolar (borne on stem beside petioles), very small, distinct, triangular. Inflorescence with the flowers borne singly or in umbels of 2–4 in axils of full-sized leaves; bracts and bracteoles eglandular, persistent, the bracteoles borne at or below apex of a well-developed peduncle. Flowers bilaterally symmetrical in all whorls, bisexual. Sepals leaving petals exposed in enlarging bud, the lateral 4 bearing large paired abaxial glands and the anterior eglandular; petals mostly described as lilac, blue, or purple, sometimes as dark rose, sometimes with white or yellowish tints, glabrous, entire, erose, or dentate, abaxially smooth or carinate on claw, the posterior petal somewhat different in size, shape, and stance from the lateral 4; receptacle glabrous on both sides of filaments; stamens 10, all fertile, glabrous, the filaments slightly connate at base, shortest opposite posterior petal; anthers subequal or larger opposite posterior-lateral petals, the connective not exceeding locules at apex; gynoecium 2- or 3-carpellate, the carpels (when 3) 1 anterior and 2 posterior, all fertile, connate their whole length in ovary; styles as many as carpels, distinct, the anterior style shorter than the posterior 2; stigmas internal or nearly terminal. Fruit dry, breaking apart at maturity into 2 or 3 samaras separating from a high pyramidal torus; samara orbicular with the lateral wing well developed, membranous with a prominent reticulum of arching anastomoses, continuous at base, the dorsal wing very small or absent or large and resembling one side of the lateral wing; fruit subtended by a fleshy 3-lobed disc or the disc rudimentary or lacking; carpophore absent. Chromosome number unknown.
Two species of Mexico, where both species grow in open deciduous woods, thorn-scrub, or desert scrub on rocky or sandy limestone slopes. [map]
Within the Malpighia clade, Calcicola is intermediate, both phylogenetically and morphologically, between Mascagnia and Malpighia. The petals of Calcicola and many species of Mascagnia are lilac, blue, or purple, which are unusual colors in this family. In Calcicola and Mascagnia the dry fruits are dehiscent, and in Calcicola and most species of Mascagnia the samaras are orbicular with the wings membranous with reticulate venation, quite different from the fleshy indehiscent fruits of Malpighia. On the other hand, in both Calcicola and Malpighia the plants are shrubs that never climb, and in Calcicola and many species of Malpighia the flowers are borne singly or in umbels of 2–4 in the axils of full-sized leaves; in Mascagnia the plants are twining vines and the inflorescence is usually an elongated pseudoraceme. Calcicola differs from both Mascagnia and Malpighia in its leaf glands, which, if present, are cylindrical and located on the lamina margin; in Mascagnia and Malpighia the glands are flat and borne in the abaxial surface between the midrib and the margin, sometimes lying very near the margin.
Photo: C. parvifolia (samaras)