Numerical taxonomy of Hoya section Hoya (Apocynaceae) from the Philippines

Abstract

The variations in leaf morphometric traits of the species under the section Hoya from the Philippines namely: (1) H. carnosa (2) H. celata, and (3) H. pubicalyx were examined. Thirty (30) mature leaf samples were randomly selected from different plant individuals for each of the Hoya species considered in this study. The collected leaf samples were immediately pressed and sun dried.  A total of twenty (20) leaf morphometric characters were selected for this study, out of this number, ten (10) were quantitative characters, while the remaining ten (10) were qualitative characters. The leaf morphometric characters were selected based on the established leaf architecture characters and terminologies defined by Hickey and the manual of leaf architecture with modifications. Measurements were manually done using a dial caliper and a protractor for angle measurements. The obtained data from the leaf morphometric characters were subjected to univariate and multivariate data analyses using PAST (Paleontological Statistical Software version 3.11) software. Results showed variations and similarities in terms of the leaf morphometric traits of the species under the section Hoya. However, considerable variations among the three Hoya species in terms of the examined leaf morphometric traits were revealed by the data analyses. Based on the results of these study, the three species, H. carnosa, H. celata and H. pubicalyx could be distinguished into three different species. This study proved the applicability of multivariate analysis as a tool and the usefulness of leaf characters in numerical taxonomic studies. The approach was able to detect variations in leaf morphometric traits and can be employed to further examine the relationships among various Hoya species and other controversial species as well.

Keywords: Hoya; variations; leaf morphometric traits; numerical taxonomy