Shrubs; stipules intra- and epipetiolar, completely connate, persistent; petiole eglandular; lamina bearing glands in abaxial surface. Inflorescence terminal, usually unbranched but sometimes ternate, each axis a raceme of short 1–7-flowered cincinni; bracts and bracteoles persistent; lowest bracteole and alternate subsequent bracteoles bearing 1 large eccentric abaxial gland; pedicel straight in bud. Sepals leaving outermost petal exposed in enlarging bud, all biglandular or anterior eglandular; corolla bilaterally symmetrical; petals bright yellow, glabrous, the anterior 2 remaining cupped one inside the other; limb of outermost petal concave; lateral petals with the margin erose; posterior petal bearing several marginal glands near base of limb, distally eglandular; androecium glabrous, bilaterally symmetrical, the anterior 7 (–9) stamens ± alike, bearing horseshoe-shaped anthers with the outer locules confluent over the apex, the posterior (1–) 3 staminodes bearing tiny rudimentary anthers; anterior 3 filaments shorter than middle 4, the staminodes much shorter; connective small, neither swollen nor extended at apex; pollen radially symmetrical, 4 (–5)-colporate; receptacle glabrous on both sides of stamens; gynoecium appearing radially symmetrical; ovary with the 3 carpels completely connate, 2 ± anterior and 1 almost posterior, with 1 fertile locule, the other 2 locules (apparently 1 anterior and 1 posterior) completely absent; styles 3, slender and subulate with the stigmas very small and slightly internal. Fruit a dry, indehiscent nut, 7–10 mm long, 4–5 mm in diameter, rugose, asymmetrical, proximally gibbous and distally sulcate, with a proximal thick-walled chamber containing the single seed and a distal thin-walled chamber containing a green oleaginous mass. Chromosome number: n = 10 (W. R. Anderson, 1993a).
Two species in Brazil: M. bahiana, in open shrubby vegetation (caatinga) on sandy soils of lowland Bahia, and M. sergipana, in sandy coastal plains (restinga) of Sergipe. Although this genus is clearly closely related to Burdachia, it differs dramatically in its habitat, petal color, reduced androecium with horseshoe-shaped anthers, reduced gynoecium, and asymmetrical fruit. The two anterior petals remain cupped one inside the other in the open flower, which is unique in the family. Anderson suggested in the protologue that the peculiar fruit might be adapted for dispersal by small rodents. [map]
Drawing: M. bahiana