| Holcoglossum is a genus of some 11 species distributed mainly in China with a few species extending to Vietnam, Thailand, Laos, and Myanmar. It is one of the problematic genera in Orchidaceae and very difficult to make a clear circumscription of Holcoglossum and its related genera. The aim of the present study is to recircumscnbe the genus, make a taxonomic revision and discuss systematics and the speciation of some species, based on both herbarium, experimental and field work.1. Morphology of Holcoglossum and some its related generaMost of the characters available in Holcoglossum and some its related genera are carefully studied both in the field and in herbaria. It seems that rostellum, column and type of pollinia are important for the circumscription of Holcoglossum and its related genera. Our study also shows that the shape of the callus, stipe and the margin of midlobe are important for the infrageneric division in Holcoglossum, while the shapes of midlobe, sidelobes, and spur are key characters to specific classification of this genus. However, the number of calli on a midlobe and of flowers on an inflorescence, as well as the length of stem are variable greatly within a species and of little significance in specific classification.2. Cytology of HolcoglossumEight species of Holcoglossum were investigated cytologically. The chromosome numbers of six species are reported for the first time. All species are 2n=38. Polyploids and aneuploids are notdiscovered in Holcoglossum. Each chromosome is less than 2 μm in length at metaphase.3. Pollination biology of Holcoglossum rupestreThe pollination system of Holcoglossum rupestre was studied in northwestern Yunnan. The species was observed to be self-compatible but pollinator-dependent and offers nectar as a reward for visitors. The beetle, Hybovalgus bioculatus Kolbe seems to be the only pollinator among all visitors observed. The insects carried the pollinia on two different positions, either the buttock or the foreleg, and pollinated the flowers by two different mechanisms. The visiting behavior of the pollinator was irregular. The analysis suggested that H. rupestre and its pollinator might be in an unstable pollination relationship. Its fruit set is low in nature. This appears to be attributed to the low visiting frequency of pollinator and the effective mechanism to prevent self-pollination. The pollination mechanisms of the genus Holcoglossum are also discussed.4. Molecular systematics of HolcoglossumThe trnL-F sequences of chloroplast genome of nine species of Holcoglossum and two species of Vanda were sequenced, and the sequences of 14 species of Vandeae, together with sequences of two American species of the subfamily Epidendroideae used as outgroups, were downloaded from Genebank. The sequenced results show that there are about 340 bp deletions in trnL-F of H. lingulatum. Parsimony analysis shows that Holcoglossum is a natural group including H. subulifolium and H. amesianum. Four Chinese species, H. sinicum, H. rupestre, H. jlavescens, and H. weixiense, are closely related, grouping into a very natural section of Holcoglossum.5. Systematics of HolcoglossumBased on herbarium and field observations, together with cytological and molecular studies, we recircumscribe the genus Holcoglossum. The genus is characterized by having the short stem,semiterete or slightly strap-shaped fleshy leaves channelled adaxially, well spaced flowers on the rachis, falcate lateral sepals, clawed petals, 3-lobed lip with purple or yellow stripes on adaxial surface of the erect sidelobes, ornamented midlobe, winged column, bifid rostellum, and two porate pollinia. As a result eleven species are recognized: H. subulifolium, H. amesianum, H. kimballianum, H. lingulatum, H. omeiense, H. quasipinfolium, H. sinicum, H. rupestre, H. flavescens, H. wangii, and H. weixiense. H. saprophyticum andH. tangii are reduced to synonyms of H. kimballianum and H. lingulatum respectively.A new infrageneric system of Holcoglossum based on our studies of morphology, phytog...
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