Systematic Significance of Leaf Epidermal Features in <i>Holcoglossum</i> (Orchidaceae)

<div><p>Determining the generic delimitations within Aeridinae has been a significant issue in the taxonomy of Orchidaceae, and <i>Holcoglossum</i> is a typical case. We investigated the phylogenetic utility of the morphological traits of leaf epidermis in the taxonomy of <i>Holcoglossum s.l</i>. by using light and scanning electron microscopy to analyze 38 samples representing 12 species of <i>Holcoglossum</i>, with five species from five closely related genera, such as <i>Ascocentrum</i>, <i>Luisia</i>, <i>Papilionanthe</i>, <i>Rhynchostylis</i> and <i>Vanda</i>. Our results indicated that <i>Holcoglossum</i> can be distinguished from the related genera based on cuticular wax characteristics, and the inclusion of <i>Holcoglossum himalaicum</i> in <i>Holcoglossum</i> is supported by the epidermis characteristics found by LM and SEM. The percentage of the tetracytic, brachyparacytic, and laterocytic stomata types as well as the stomata index and certain combinations of special wax types support infrageneric clades and phylogenetic relationships that have been inferred from molecular data. Laterocytic and polarcytic stomata are perhaps ecological adaptations to the strong winds and ample rains in the alpine region of the Hengduanshan Mountains.</p>