Anatomy and systematics of Dendroseris (sensu lato)

Abstract

Anatomical study of the genusDendroseris (Compositae: Cichorieae), endemic to the Juan Fernandez Islands, was undertaken to determine if segregate genera were valid. Other questions include the significance of pith bundles and of receptacular bristles, and whether the ancestors of these peculiar rosette trees and shrubs were woody or herbaceous. Anatomical evidence, when added to that from gross morphology, suggests that the segregation as distinct genera ofRea, Phoenicoseris, andHesperoseris is probably not justified, and that they are better treated as subgenera ofDendroseris. Differences in pollen morphology, floral trichomes, achene and leaf anatomy provide good species characteristics. These all appear, respectively, as variations on a basic plan, andDendroseris can be envisaged as derived from a common stock in the Juan Fernandez Islands. The genus is not particularly primitive within the family or tribe. The presence of additional bundles in the flowers ofD. litoralis may be interpreted as related to gigantism. The separate corolla lobes inD. gigantea probably do not represent a vestige of an actinomorphic condition. Pith bundles inDendroseris may have been present in ancestors; in any case, they seem likely to have increased in prominence with increase in stem diameter. Available evidence seems to favor the interpretation of growth forms inDendroseris as derived from an herbaceous ancestry.