The new genus and species Mahechadendron puntecascarillo are described based on specimens first collected in the ‘60s but only recently found with flowers and fruits. It grows in the moist forests of the Middle Magdalena River in Colombia. The highly durable wood of this forest tree species is still used intensively for construction. Morphological and rbcL sequence data place this genus in the Vochysiaceae, most likely closely related to Callisthene. Mahechadendron shows inflorescences in compound dichasia, compact, only developed laterally, traits not previously recorded in this family. Mahechadendron puntecascarillo exhibits the tiniest flowers known in the Vochysiaceae, with the fourth sepal basally sacciform, and copious villous-lanose indumentum in the internal portions of the fourth sepal, petal, filament, and ovary; the flowers also have the single petal non-clawed, a feature not very common in Vochysiaceae. In addition, the capsular fruit has a thick and persistent central column, and the exocarp is fused to the endocarp even at maturity, with seeds unilaterally winged. Moreover, this species bears mirror-image flowers, indicating enantiostyly, a sexual polymorphism already known in some Vochysiaceae. The conservation status suggested for the new species is Endangered (EN). A key to the genera of Vochysiaceae is provided.