An evolutionary investigation of the New Zealand inuleae (compositae): Stem anatomy and flowering phenology

Abstract

Evidence for systematic relationships and evolutionary processes in the New Zealand Inuleae (Compositae) is examined, by investigating the stem anatomy and flowering phenology of selected, representative species. The stem anatomy of 51 species of Inuleae from New Zealand and Tasmania is described using transverse sections of the primary stem near the apex, mature primary stem, and mature secondary stem. Results from the stem anatomy provide a number of features which are available for systematic interpretation, including the occurrence of anomalous secondary growth in three species of Raoulia, the presence of resin canals in Haastia, and the occurrence of a Casparian strip. The groupings suggested by phenetic and cladistic analyses of the stem data support affinities that have already been identified in the literature, but also suggest new groupings which should be investigated. The flowering phenology of 16 species which occur in the Cass District are described at the association, population, individual, capitulum, and floret levels. Patterns are discussed with reference to observations on floral visitors, breeding systems and habitat. It is suggested that a highly staggered flowering pattern observed in the species growing on the riverbed may have resulted from selection imposed by the occurrence and timing of floods and pollinator competition via interspecific pollen transfer. Hypotheses as to the functional significance of the phenology patterns are presented, including adaptations to avoid geitonogamy and interference between male and female functions, adaptations to specific pollinators, and opportunistic life styles. It is hypothesised that the short life span of trinucleate pollen creates a hereto unrecognised phylogenetic constraint on the evolution of the Compositae capitulum.