Bidens pilosa Complex (Asteraceae) in North and Central America

Abstract

Field observations, chromosome counts, flavonoid chemistry, breeding system data, hybridization experiments, and a quantitative analysis of twelve morphological features combine to show that the North and Central American populations of B. pilosa sensu Sherff actually include three distinct species: B. odorata (n = 12), B. alba (n = 24), and B. pilosa (n = 36). All these taxa are square-stemmed, white-rayed or discoid annuals with linear, obcompressed-quadrangulate achenes, but each species can be distinguished morphologically by differences in ray length and width, in outer phyllary length, width and shape and chemically by differences in the chalcones accumulated in their leaves. New combinations are proposed and two varieties, B. odorata var. oaxacensis and B. odorata var. chilpancingensis, are described as new. Descriptions, distribution maps, synonymies, and a key to all taxa are provided.