Aspects of comparative vegetative morphology as an aid to Actinidia taxonomy.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This study explores the practical value of comparative morphology as an aid to Actinidia taxonomy, using vegetative characters derived from spring and summer shoots of 20-30 taxa, selected from the “NZ D.S.I.R. Actinidia germplasm collection” at Auckland and Te Puke during 1988-1989. Data are collected from field-based observations and from samples processed for light and electron microscopy; these are supplemented with observations derived from herbarium specimens collected in China. The taxonomic potential of characters is further tested using multivariate and other statistical methods. Actinidia are morphologically variable vines which, nevertheless, express genetically-determined form in: their manner of climbing, the types and growth characteristics of shoots and in the ontogenetic expression of shoot form. There is however a strong “opportunistic component” in the realisation of plant form. Some more conservative characters include leaf venation pattern, trichome morphology, arrangement of sclerenchyma fibres and the complement of ergastic crystals associated with vascular bundles of the leaf. Microscopic examination of abaxial foliar trichomes, currently used to demarcate sections of the genus, reveal branched hair types in Maculatae and Strigosae, which are supposed to be absent (Dunn 1911, Liang 1984) from these sections of the genus. Re-examination of these groups and the characters delimiting them is recommended. Comparative morphological studies of Actinidia in the germplasm collection show that many of the characters of winter-dormant shoots are genotypic in nature. Vines of Leiocarpae and Stellatae may be identified below the species level by their bud-form characteristics. Discriminant analysis shows the value of bud height and ostiole size in separating major taxonomic and geographic groups. Detailed analysis of bud characters is justified as poor or uneven budbreak currently limits the productivity of commercial cultivars. Taxonomists need to be more aware of the spatial and temporal potential afforded by vegetative morphological characters in this genus. The discovery of “water-excreting glands” (= hydathodes) in all Actinidia seen, culminating in a combination of “water spending” characters in A. deliciosa, has important implications for water-relations in these plants. Hydathodes in A. deliciosa are well supplied by craspedodromous venation and the ultimate tracheids terminate in a spatially diffuse but metabolically active environment, in the apices of these glands. The fate and functioning of hydathodes in Actillidia needs further research. The results from this exploratory study are intended to contribute to the programme of genetic and taxonomic studies of Actinidia; currently being undertaken by D.S.I.R. Fruit and Trees, Auckland.