Trees, shrubs, erect or trailing subshrubs or herbs with perennating underground structures, or woody to herbaceous (but perennial) vines climbing by twining stems; hairs unicellular, usually 2-armed and medifixed or submedifixed, basifixed or stellate in a few genera.
Stipules usually present beside or on the petiole or axillary to it, distinct or variously connate, minute to more than 14 cm long, absent in some genera or species.
Leaves mostly opposite and decussate, sometimes whorled, subopposite, or alternate, often bearing large multicellular glands on the petiole or lamina (usually the abaxial surface or margin) or both; lamina simple, mostly entire (rarely lobed), the margin never truly toothed but sometimes pseudodentate or ciliate at the location of marginal glands or stout bristle-like hairs.
Inflorescences terminal or axillary, very diverse, most often racemose or paniculate but with the flowers often borne ultimately in umbels or corymbs of 4 or more; floriferous pedicel mostly well developed, terminating proximally in a joint.
Flowers small (about 6 mm in diameter) to fairly large (about 4 cm in diameter), mostly bisexual (a few genera dioecious or functionally dioecious), subtly to strongly bilaterally symmetrical or, in some genera, radially symmetrical, hypogynous except perigynous in Barnebya, mostly all alike and chasmogamous but a few genera with showy chasmogamous flowers and tiny reduced cleistogamous flowers borne ± simultaneously. Sepals 5, persistent, mostly imbricated in bud, distinct or partially connate at base or adnate to the receptacle, the great majority of New World taxa bearing (1) 2 large multicellular abaxial glands on all 5 sepals or on the lateral 4, most Old World taxa with the calyx glands much reduced in number and size or absent. Petals 5, distinct, mostly clawed, alternating with the sepals, imbricated with the posterior innermost and 1 of the anterior-lateral pair outermost, most often yellow, pink, or white, sometimes other colors but very rarely blue, the posterior ("flag") petal often different from the lateral 4. Androecium mostly of 10 stamens in a single whorl, fewer in some genera, up to 15 in Lasiocarpus, borne on the receptacle between perianth and gynoecium, the filaments always present, short to long, alike or heteromorphic, distinct or partially connate, the anthers alike or heteromorphic, 4-locular, mostly longitudinally dehiscent along the inner edge of each locule, a few genera with apical or subapical pores or very short slits. Gynoecium superior, usually comprising 3 distinct to connate carpels, mostly 1 anterior on the plane of symmetry and 2 posterior on each side of the plane of symmetry, the carpels only 2 in several genera and very rarely 4, mostly all fertile, each fertile locule containing 1 pendent anatropous ovule, the styles mostly as many as carpels and distinct, connate or reduced in number in a few genera.
Fruits fleshy or dry; fleshy fruits mostly an indehiscent drupe or berry, yellow, red, blue, or black, of a size to suggest dispersal by birds; dry fruits indehiscent in a few genera, but in most splitting apart into mericarps (mostly up to 3); dry fruits or mericarps of some genera nutlets without any obvious adaptation for dispersal, those of some genera or species containing aerenchyma or other tissues that facilitate dispersal by water, but most bearing wings or setae and dispersed by wind. Seeds 1 per locule or mericarp, never released (i.e., dehiscence never loculicidal, or at least not sufficiently so to allow the seed to escape), without endosperm.
Chromosome Numbers. In Malpighiaceae the lowest number known is n=6, and that may well be the ancestral number, because it occurs in three genera of the Galphimia clade (Galphimia, Lophanthera, and Verrucularia), near the base of the phylogenetic tree (see Davis et al., 2002 [pdf]). Most numbers in the family are n=10 or 12 or multiples of those numbers, or numbers that are presumably aneuploid derivatives of those numbers, e.g., n=8 in Ectopopterys, n=9 in Cordobia, and n=17 in Camarea (W. R. Anderson, 1993a [pdf]).