Numerical Taxonomy of the Hoya parasitica (Asclepiadaceae) complex in Thailand

Abstract

Hoya parasitica sensu lato is a climbing epiphyte of the family Asclepiadaceae. At present, the taxonomic status of this species in Thailand is still indeterminate due to the great variation in size, shape and color of the leaves and flowers. Therefore, this plant is referred to as the H. parasitica complex. A previous study on morphological and anatomical variations of the complex showed that nine forms (Form I-IX), based on leaf shape, form of leaf base, leaf venation, leaf indumentum, shape of sepal, and shape of coronal scale, could be recognized. In this present study, two techniques of numerical taxonomy were used to investigate the taxonomic status of these forms in the Hoya parasitica complex in Thailand. To facilitate this latter investigation, 534 specimens (OTUs) of the nine morphological forms collected from their natural habitats throughout Thailand, were analysed using cluster and canonical discriminant analyses. A total of 35 quantitative and 14 qualitative characters were employed. In cluster analysis using only quantitative characters, the complex could be separated into three groups; i.e. Form I, Form II, and Form III-IX at average taxonomic distance 1.80. The same result was obtained when both quantitative and qualitative characters were used. Likewise, canonical discriminant analysis suggested the occurrence of three groups within the complex. The important characters used for separating these three groups are sepal length, corpusculum width, and leaf width. As a result of our findings, it is proposed here that the H. parasitica complex in Thailand should be treated as 3 species; i.e. H. rigida Kerr (Form I), Hoya sp. nov. (Form II) and H. parasitica (Roxb.) Wall. ex Wight ( Form III-IX).