Monophyly or Paraphyly– The Taxonomy of <em>Holcoglossum</em> (Aeridinae: Orchidaceae)

<div><p>Recently, there have been a lot of intense debates about the acceptance/rejection of paraphyletic groups in biological classification. On the one hand, evolutionary classification states that similarity and common descent are two criteria for biological classification and paraphyletic groups are natural units of biological classification. On the other hand, cladistic classification considers that common descent is the only criterion in biological classification and monophyly should be strictly adhered to. <em>Holcoglossum</em> is used herein as a case to illustrate this problem. Although <em>Holcoglossum</em> is a small orchid genus of less than 20 species, there is little consensus about its generic circumscription since it was established, which leads to confusion in taxonomic treatments in the <em>Aerides-Vanda</em> group. Based on the analyses of molecular and morphological evidence, our results suggest that the clade comprising <em>Holcoglossum</em> s.s., <em>Ascolabium</em>, <em>Penkimia</em> and <em>Ascocentrum himalaicum</em> is strongly supported as a monophyly, and that the three taxa are nested within different subclades of <em>Holcoglossum</em> s.s. Thus, it is reasonable to recognize a monophyletic circumscription of <em>Holcoglossum</em>, which is also well supported by some vegetative and floral characters. The <em>Holcoglossum</em> s.l. would facilitate a better understanding of pollinator-driven floral divergence and vegetative stasis than a paraphyletic and narrowly defined genus.</p>