Rudolphia Medik., Malvenfam. 111–112. 1787.—Type: R. edulis Medik., nom. superfl. [M. urens L.].
Shrubs or trees up to 10 (–24) m tall; stipules interpetiolar, mostly distinct, connate in interpetiolar pairs in a few species; leaves decussate; petiole eglandular; lamina usually bearing 2–4 (–10) glands impressed in abaxial surface. Inflorescence axillary, an unbranched pseudoraceme congested in most species into a dense corymb or umbel, in some species with only 1-2 flowers; bracts and bracteoles eglandular; pedicels pedunculate. Flowers bilaterally symmetrical in calyx, corolla, and androecium; sepals mostly bearing 6 large glands on 3, or also 1–4 (often smaller) glands on the other 1–2 sepals; petals pink, lavender, or white, glabrous or nearly so; stamens 10, all bearing fertile anthers, the anthers subequal or the 2 opposite the posterior-lateral petals larger; gynoecium with the carpels 3, completely connate in the ovary in most species; styles 3, stout, cylindrical, the apex with a large internal or subterminal stigma and dorsally rounded, truncate, or hooked. Fruit fleshy, mostly indehiscent, drupes or berries, usually red at maturity, with 3 pyrenes united in the center or distinct at maturity but then usually retained in a common exocarp (separating in a few species), the hard wall of each pyrene showing rudimentary dorsal and lateral wings and sometimes rudimentary intermediate winglets or dissected outgrowths (see discussion of M. leticiana below). Chromosome number: n = 10 (M. glabra) (W. R. Anderson, 1993a).
At least 50 species, and possibly as many as 100 (see note below under References).
Malpighia is one of three genera in the Malpighiaceae that produce cherry-sized fleshy fruits attractive to birds; the other two are Bunchosia and Byrsonima. The three are easily distinguished on the basis of morphology, and many years ago W. Anderson (1978a, pdf) asserted that Malpighia was derived from a wing-fruited mascagnioid and did not share a recent common ancestor with either Bunchosia or Byrsonima. The most recent phylogeny of the family (Davis & Anderson, 2010 [pdf]) shows that Malpighia is in a clade with the New World genera Calcicola and Mascagnia, both dispersed by lateral-winged samaras, and a number of Old World genera, all dispersed by lateral-winged samaras, except the very derived Malagasy genus Rhynchophora.
Aside from the fleshy fruits, Malpighia is notable for the non-vining habit, the interpetiolar stipules, the glands in the abaxial surface of the leaves, the unbranched axillary inflorescences, and the pink, lavender, or white petals.
The mysterious species Malpighia leticiana, known only from its type, deserves special comment. Its immature fruit bore coriaceous, probably succulent lateral wings, which originally led to its being described in Mascagnia. The latest phylogeny (Davis & Anderson, 2010 [pdf]) shows it to be embedded among the Mexican species of Malpighia, for which reason it was reassigned to Malpighia. Its fruit presumably represents some kind of reversal to an ancestral condition; further comment is not possible until it is better known. See the discussion of this species and of the problem of distinguishing Malpighia from Mascagnia in Anderson & Davis (2005b).
About half the species of Malpighia grow in Mexico and Central America, and the other half in the West Indies. The only species in South America are in the northwest and are also in Central America and Mexico, suggesting that they may represent northern species that migrated southward. The Mexican endemic Calcicola is sister to Malpighia (Davis & Anderson, 2010 [pdf]), which suggests that Malpighia may have originated in Mexico.
References: Vivaldi (1979) in his Ph.D. thesis on Malpighia recognized 38 species, including a number of subspecies. Owing to his untimely death, his work was never published, except for three new Jamaican species (1982) and three new subspecific taxa (1984 [pdf]).—Meyer (2000) published a revision of Malpighia in which he recognized 130 species, including ca. 50 new species mostly from the West Indies. Many of his species were based on slight differences between populations, and it remains to be seen how many of them will gain long-term acceptance by other botanists. [Meyer's book lacks an index; an unpublished index compiled by W. R. Anderson is available here: pdf]. González G. (2015) added a new species from Cuba.—The generic description given above was based on published (2007c [pdf]) and unpublished work of W. R. Anderson.
Etymology: The name Malpighia honors the Italian anatomist Marcello Malpighi (1628–1694), one of the first to use the compound microscope to study the fine structure of animals and plants. Plumier in his book Nova Plantarum Americanarum Genera (1703) chose the name to commemorate Malpighi, and Linnaeus followed Plumier when he published his Genera plantarum in 1737.
Uses: Malpighia emarginata is widely cultivated for its fleshy fruits, which are rich in vitamin C; common names for it include acerola, Barbados cherry, and cereza. It has long been known as M. punicifolia, but the type of that name is a specimen of M. glabra. There continues to be great confusion in horticultural circles over the application of these names, with many using M. glabra and M. emarginata as if they were interchangeable and calling the cultivated acerola M. glabra. Both species are available in the horticultural trade in the United States as ornamental shrubs, and because they are similar and difficult to distinguish the plants offered for sale are often misidentified. They can be distinguished by the following key:
|1.||Leaves usually short- to long-acuminate at apex, occasionally acute, evenly spaced, successive pairs separated by well-developed internodes.|
M. glabra L.
|1.||Leaves usually rounded or obtuse at apex and often emarginate or apiculate, some pairs crowded in dense shoots with very short internodes, others separated by much longer internodes.|
M. emarginata DC.
Some other species of Malpighia are grown as dooryard plants for their edible fruits, but the extent of that use is difficult to document; M. mexicana is one of those. Malpighia coccigera is cultivated worldwide in warm climates and in greenhouses as a miniature ornamental shrub; its common name is "dwarf holly."