Rheophytes of the middle Caquetá River, Colombian Amazonia

We studied the rheophytic vascular flora of the middle Caquetá River basin in the Colombian Amazon, by sampling along the margins and islands of its two largest rapids, Angostura and Araracuara, along the rapids of the black-water Yarí river, its second largest tributary, and along a swift black-water creek flowing from a small Tepui into the latter. We identified and quantified rheophytes in 12 plots and col-lected other rheophytic species spotted outside the plots. We found 28 species of rheophytes, belonging to 20 families, mostly herbs and subshrubs. The rheophytic flora of the white-water Río Caquetá only shared three species, with that of the Yarí River; instead, the Yarí River shared no rheophytic species with its tributary creek, despite being just a few meters away. The family Podostemaceae dominates the extreme rheophytic belt, where the current hits the strongest. The most diverse families were Myrtaceae, and Xyridaceae (three species each); Acanthaceae (two species) is the most diverse family in the middle level, whereas Myrtaceae (three species) predominates in the upper rheophytic belt of small trees, and makes up a transition between the truly rheophytic and the riparian floras. The most abun-dant and frequent species was Pfaffia iresinoides (Amaranthaceae). Eight species are endemic to this area, and no species is shared with the other Neotropical areas where rheophytes have been surveyed.