ANCIENT VICARIANCE OR RECENT LONG-DISTANCE DISPERSAL? INFERENCES ABOUT PHYLOGENY AND SOUTH AMERICAN–AFRICAN DISJUNCTIONS IN RAPATEACEAE AND BROMELIACEAE BASED ON ndhF SEQUENCE DATA

Rapateaceae and Bromeliaceae each have a center of diversity in South America and a single species native to a sandstone area in west Africa that abutted the Guayana Shield in northern South America before the Atlantic rifted. They thus provide ideal material for examining the potential role of vicariance versus long-distance dispersal in creating amphiatlantic disjunctions. Analyses based on ndhF sequence variation indicate that Rapateaceae and Bromeliaceae are each monophyletic and underwent crown radiation around 41 and 23 Ma, respectively. Both exhibit clocklike sequence evolution, with bromeliads evolving roughly one-third more slowly than rapateads. Among rapateads, the divergence of west African Maschalocephalus dinklagei from its closest South American relatives implies that Maschalocephalus resulted via long-distance dispersal 7 Ma, 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, to a lesser extent, in Amazonia and the Brazilian Shield. Speciation at small spatial scales accelerated 15 Ma with the invasion of high-elevation, insular habitats atop tepuis. Among bromeliads, Pitcairnia feliciana diverges little from its congeners and appears to be the product of long-distance dispersal ca. 12 Ma. Brocchinia/Ayensua and then Lindmania are sister to all other bromeliads, indicating that the Guayana Shield was also the cradle of the bromeliads. Three lineages form an unresolved trichotomy representing all other bromeliads: (1) Tillandsioideae, (2) Hechtia, and (3) a large clade including remaining genera of Pitcairnioideae and all Bromelioideae. The last includes a clade of pitcairnioid genera endemic to the Guayana and Brazilian Shields; a xeric group (Abromeitiella/Deuterocohnia/Dyckia/Encholirium/Fosterella) from southern South America and the southern Andes, sister to Pitcairnia; and Andean Puya, sister to Bromelioideae, with many of the latter native to the Brazilian Shield. Both Rapateaceae and Bromeliaceae appear to have arisen at low elevations in the Guayana Shield, experienced accelerated speciation after invading dissected mountainous terrain, and undergone long-distance dispersal to west Africa recently. Bromeliad acquisition of key adaptations to drought (e.g., CAM photosynthesis, tank habit, tillandsioid leaf trichomes) 17 Ma appears to have coincided with and help cause the centripetal invasion of drier, more seasonal regions beyond the Guayana Shield, resulting in a wider familial range and dominance of the epiphytic adaptive zone. Geology, past and present climate, and proximity to South America help account for both families occurring in nearly the same area of Africa. We present a new classification for Rapateaceae, including a new tribe Stegolepideae, a new subfamily Monotremoideae, and revisions to tribe Saxofridericieae and subfamily Rapateoideae.