Monophyly or Paraphyly– The Taxonomy of Holcoglossum (Aeridinae: Orchidaceae)

Abstract

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. Holcoglossum is used herein as a case to illustrate this problem. Although Holcoglossum 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 Aerides-Vanda group. Based on the analyses of molecular and morphological evidence, our results suggest that the clade comprising Holcoglossum s.s., Ascolabium, Penkimia and Ascocentrum himalaicum is strongly supported as a monophyly, and that the three taxa are nested within different subclades of Holcoglossum s.s. Thus, it is reasonable to recognize a monophyletic circumscription of Holcoglossum, which is also well supported by some vegetative and floral characters. The Holcoglossum s.l. would facilitate a better understanding of pollinator-driven floral divergence and vegetative stasis than a paraphyletic and narrowly defined genus.

A molecular phylogeny of Aeridinae (Orchidaceae: Epidendroideae) inferred from multiple nuclear and chloroplast regions

“…Recent 62 phylogenetic analyses that relied on nucleotide sequences have 63 addressed relationships in the group. With the exception of several 64 studies focusing on some individual groups, such as the Vanda alliance (e.g., Kocyan et al, 2008;Gardiner et al, 2013;66 Xiang et al, 2012;Zhang et al, 2013) and Phalaenopsis (e.g., 67 Padolina et al, 2006;Tsai et al, 2010;Yukawa et al, 2005), the phy-68 logeny of Aeridinae was reconstructed by Topik et al (2005) and 69 Topik et al (2012) based on the analyses of two DNA regions (ITS 70 and matK) in 75 taxa belonging to 62 genera and 82 taxa belonging 71 to 66 genera, respectively. Both studies suggested that the mono-72 phyly of Aeridinae was tentatively supported.…”

“…Wood (1990) lyses may lead to incorrect topologies (Meimberg et al, 2006). Of all of the taxa in Aeridinae, this group has recently received 327 the most attention (Christenson, 1987;Gardiner, 2012;Gardiner 328 et al, 2013;Liu et al, 2011;Xiang et al, 2012;Zhang et al, Seidenfaden, 1992). In fact, the greatest difference between the 393 two genera is that Trichoglottis has short inflorescences and the lat-394 ter has long inflorescences.…”

“…However, it shares slender and cylindrical 368 leaves with Papilionanthe and Paraphalaenopsis. In some cases, the 369 floral traits do not mirror phylogeny, which is attributed to pollina-370 tor-mediated evolution (e.g.,Kocyan et al, 2008;Xiang et al, 2012).Flat leaves, larger viscid discs than stipes and moderately large 373 flowers are the traits shared by the members of the Aerides clade. Through additional sampling, our analyses propose close relation-375 ships among Aerides, Arachnis, Esmeralda and Renanthera, which is 376 not in agreement with the close relationships between Aerides and Christensonia + Turdelia obtained in the study conducted by Topik 378 et al (2005).…”

Potential pollinator of Vanda falcata (Orchidaceae): Theretra (Lepidoptera: Sphingidae) hawkmoths are visitors of long spurred orchid

“…Most of Holcoglossum and Papilionanthe have whitish flowers and relatively long spurs (ca. 1-1.5 cm; Topik et al, 2005;Kocyan et al, 2008;Xiang et al, 2012), which may be pre-adaptations to pollination by moths.…”

Systematic Significance of Leaf Epidermal Features in Holcoglossum (Orchidaceae)

“…Christenson [10] divided Holcoglossum into two sections based on the flower number per inflorescence and plant form. Jin [12] proposed an infrageneric system based on floral characteristics, such as the callus, spur and stipe; this system has been supported by the results of recent molecular phylogenetic studies [13], [20]. However, four species in Jin's system, H. omeiense X. H. Jin & S. C. Chen, H. lingulatum (Averyanov) Averyanov, H. wangii Christenson and H. kimballianum (Rchb.…”