Rapateaceae and Bromeliaceae are closely related families of commelinid monocots, each with a center of diversity in South America, and each with one species in West Africa. In Rapateaceae, monotypic Maschalocephalus is endemic to a sandstone area that abutted the South American Guayana Shield before the Atlantic rifted. In Bromeliaceae, Pitcairnia feliciana occurs on Bioko, and is large genus ranging throughout Central and South America. Phylogenies based on ndhF sequence variation identify both families as monophyletic, and are consistent with clock-like rates of sequence evolution. The divergence of Maschalocephalus from its closest South American relatives implies that it is the product of long-distance dispersal roughly 6 Mya, not ancient continental drift; only its sandstone habitat is vicariant. Rapateads arose first at low elevations in the Guayana Shield; the earliest divergent genera are widespread along riverine corridors there and in the Brazilian Shield and Amazonia. Speciation at small spatial scales accelerated roughly 24 Mya, with the invasion of high-elevation, insular habitats atop tepuis. In Bromeliaceae, Pitcairnia feliciana diverges little from its congeners and also appears to be the product of recent, long-distance dispersal. Brocchinia/Ayensua, and then Lindmania are sister to all other bromeliads, indicating that the Guayana Shield was also the cradle of the bromeliads; the earliest divergent Brocchinia is also native to low elevations there. Tillandsioideae diverged after Lindmania, then another clade of tepui genera (Navia/Brewcaria/Sequencia), and then a xeric clade (Abromeitiella/Deuterocohnia/Dyckia/Enchorlirium) sister to Pepinia/Pitcairnia and allied to Fosterella. Finally, Andean Puya is sister to Bromelioideae, mostly of the Brazilian Shield. Thus, both families appear to have arisen at low elevations within the Guayana Shield, and then undergone long-distance dispersal relatively recently to West Africa. The available data suggest that a parallel history may also characterize Mayacaceae, another commelinid family sister to Xyridaceae/Eriocaulaceae and closely allied to Rapateaceae and the Cyperales.

Key words: biogeography, commelinid monocots, Guayana Shield, Long-distance dispersal, vicariance