Calibration, verification and stepwise analysis for numerical phenetics: Olinia (Oliniaceae) as an example

Calibration and verification techniques are discussed in the context of numerical phenetic analysis. Calibration is introduced to evaluate the character set, decide on the type of phenetic algorithm to be used, and determine the level at which to recognize taxonomic entities. Clusters are verified by analyzing sub-samples of specimens. This determines whether the groups obtained are dependent on the variation represented by particular specimens or on variation between taxa to which the specimens belong. A stepwise procedure was used to improve resolution on the ordination axes and thus to visualize differences between phenetically similar taxa. The application of these techniques in Olinia Thunb. supports the recognition of six clearly defined clusters which correspond to O. emarginata Burtt Davy, O. micrantha Decne, O. ventosa (L.) Cufod., O. capensis (Jacq.) Klotzsch, O. radiata Hofmeyr & Phill. and O. vanguerioides Bak. The analyses further revealed one highly variable group, referred to as the O. rochetiana complex, which includes O. aequipetala (Del.) Cufod, O. usambarensis Gilg, O. volkensii Engl., O. macrophylla Gilg, O. ruandensis Gilg, O. discolor Mildbraed and O. huillensis Welw. ex A.R. Fernandes.