COMPARATIVE MORPHOLOGY OF THE CAPITULUM OF ENCELIOPSIS (ASTERACEAE: HELIANTHEAE)

Features of the capitula of all four species of Enceliopsis were examined with light and scanning electron microscopy, measured, and subjected to univariate analysis. Differences were found in the complement, distribution, and density of trichomes, the size of the receptacle, ray ligule, and disk corolla tube, and the size and shape of the phyllaries, paleae, disk corolla throats, and achenes. Morphology of trichomes, phyllaries, and achenes, as well as other vegetative characteristics, show that E. nudicaulis, E. covillei and E. argophylla form a group separate from E. nutans. Features of the achene suggest affinity of the former group with Geraea, whereas features of the trichomes and achene of E. nutans support affinity with Encelia. Characters of the receptacle, paleae, ray and disk corollas, and achene clearly show that E. nudicaulis, E. covillei, and E. argophylla are distinct.