Systematic Significance of Leaf Epidermal Features in Holcoglossum (Orchidaceae)

Abstract

Determining the generic delimitations within Aeridinae has been a significant issue in the taxonomy of Orchidaceae, and Holcoglossum is a typical case. We investigated the phylogenetic utility of the morphological traits of leaf epidermis in the taxonomy of Holcoglossum s.l. by using light and scanning electron microscopy to analyze 38 samples representing 12 species of Holcoglossum, with five species from five closely related genera, such as Ascocentrum, Luisia, Papilionanthe, Rhynchostylis and Vanda. Our results indicated that Holcoglossum can be distinguished from the related genera based on cuticular wax characteristics, and the inclusion of Holcoglossum himalaicum in Holcoglossum 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.

Evolution of plastid genomes of Holcoglossum (Orchidaceae) with recent radiation

“…Biogeographic analyses and molecular phylogeny suggest that Holcoglossum dispersed from tropical regions to the HDM and then radiated there [23]. Previous results indicated that the pendent growing pattern [23] and laterocytic and polarcytic stomata are perhaps ecological adaptations to the strong winds and ample rains in the alpine region of the HDM [26]. Rapid changes in temperature and weather conditions are major challenges for the species living in temperate alpine regions in the HDM.…”

Leaf anatomical characters of four epiphytic orchids of Sempu Island, East Java, Indonesia: The importance in identification and ecological adaptation

“…Moreira et al (2013) showed the leaves of Epidendrum secundum growing in the luminous area had a relatively thick cuticle, indicating adaptation to the environment with intense solar radiation, with cuticle functions as a barrier to reduce transpiration because of the high intensity of sunlight. Fan et al (2014) demonstrated other anatomical characters showing structural adaptation in other orchids. They reported that Holcoglossum had structural adaptations to strong winds and ample rains in subalpine region of the Hengduans Mountains by having laterocytic and polarcytic stomata in their leaf epidermal layer.…”

“…This result indicates that D. subulatum had more adaptive ability to coastal habitats compared to other orchid species in Sempu Island. Other studies also showed that other orchids species have adaptive anatomical characters, such as Epidendrum secundum growing in luminous area had relatively thick cuticle (Moreira et al (2013); Holcoglossum growing in subalpine region of mountainous area possessed laterocytic and polarcytic stomata in their leaf epidermal layer showing structural adaptation to strong winds and ample rains (Fan et al 2014).…”

“…Anatomical features are important characters to support identification and classification in Orchidaceae (Pridgeon 1982;Aybeke et al 2010, Fan et al 2014. Pridgeon (1982) and Pridgeon and Norris (1979) showed diagnostic Anatomical characters have been shown to have the relationship with the ecological adaptation of orchids.…”

A New Species of Cleisostoma (Orchidaceae) from the Hon Ba Nature Reserve in Vietnam: A Multidisciplinary Assessment

“…Anatomical data may provide clues for phylogenetic relationships and taxonomic identifications because anatomy is usually less affected by environmental conditions than (macro)morphological characters. This promise has been fulfilled in several orchid groups (e.g., [ 13 – 17 ]), including the genus Holcoglossum from Aeridinae [ 18 ]. Possibly, anatomy may help to resolve taxonomic complexities in Cleisostoma , however, only little is known about anatomical variation in the tribe Vandeae.…”