Taxonomic revision of the Hoya parasitica complex in Thailand

Abstract

Hoya parasitica sensu lato is a climbing epiphyte, belonged to the family Asclepiadaceae. At present, taxonomic status of this species in Thailand is still dubious due to its great variations in size, shape and color of leaf and flower. In order to investigate this doubtful taxon, 534 specimens were collected from their natural habitats throughout Thailand. Based on qualitative morphological and anatomical characters, the H. parasitica complex can be divided into 9 forms (form I-IX). They can be distinguished mainly based on leaf shape, leaf base, venation pattern, leaf indumentum, and shapes of sepal, corona and corpusculum. Multivariate morphometric analyses of 35 quantitative morphological characters revealed the separation of 534 specimens (OTUs) into 3 groups, i.e. form I, form II, and forms III-I X. The important characters used for separating these three groups are sepal length, corpusculum width, and leaf width. The PCR-RFLP technique was subsequently used to detect diversity of chloroplast DNA in H. parasitica complex. Accounting for 20% of the total chloroplast genome, nine different cpDNA regions were amplified with the universal primer pairs. The amplified products of each primer pair were then digested by fourteen restriction enzymes. Nine combinations (C1C1-MspI, CD-AseI, TC-TaqI, K2QhHinf I, K2Q-TaqI, VL-TaqI, VL-Rsa I, K1K2-EcoRI, and K1K2-AseI) showed polymorphic patterns being distributed over 12 haplotypes. The result of PCR-RFLP technique showed a closely relationship among the members of H. parasitica complex and there is a low potential utility of this technique in characterization of the recognized nine forms of the complex. In all, it is proposed there that the H. parasitica complex in Thailand should be treated as 3 species; i.e. H. rigida Kerr (form I), H. sp. (form II) and H. parasitica (Roxb.) Wall. Ex Wight which included 2 forma according to coronal scale shape (ovate-elliptic and ovate-lanceolate).