Grade of Membership models reveal geographical and environmental correlates of floristic structure in a temperate biodiversity hotspot.

Identifying the contours and correlates of species turnover is central to understanding the nature of biogeographical regions. The Hengduan Mountains region of south-central China (HMR) is well known for its high diversity of plants, but its boundaries and internal floristic structure are poorly understood, especially in relation to geographical and environmental factors. With data on occurrences and elevational ranges of seed plants across the HMR and adjacent areas of the greater Qinghai-Tibet Plateau, we identified motifs (distinct species assemblages) by Grade of Membership models, and characterized relative contributions of geography, elevation, and climate to their spatial patterns. Motifs segregate primarily by latitude, elevation, and correlated environmental variables, most sharply across the tropical-temperate divide. Secondarily, they segregate by longitude and geographical features, and reveal a novel divide across the Jinsha River. A core set of motifs corresponds to previous delineations of the HMR. The HMR biodiversity hotspot is more a mosaic of floristic elements than a cohesive entity. Grade of Membership models effectively reveal the geographical contours of biotic structure, and are a valuable new tool for biogeographical analysis.

Perrottetiataronensis B.M.Barthol. & K.Armstr., sp. nov. (Dipentodontaceae), a new species from northwestern Yunnan Province, China and northern Kachin State, Myanmar and a re-examination of the Asian and Australasian taxa of Perrottetia.

Perrottetiataronensis from the Dulong Jiang valley in northwestern Yunnan Province, China and the Babulongtan mountain range in northern Kachin State, Myanmar is here described as a new species of the Dipentodontaceae. It is the third species of the genus to be recognized for China and the first to be reported for Myanmar. It is similar to P.alpestris s.s. but differs by characters of its leaf margins, inflorescences, and fruit. The three subspecies of P.alpestris recognized by Hou in "Flora Malesiana" are here recognized as three distinct species, i.e., P.alpestris, P.moluccana, and P.philippinensis on the basis of differences in diagnostic characters and distribution. The report in the "Flora of China" of the Taiwan species P.arisanensis from Yunnan is determined to be incorrect due to misidentification of two specimens at KUN.

A cytological study on Kelloggia (Rubiaceae), an intercontinental disjunct genus between eastern Asia and western North America.

A cytological study was carried out for the first time on four populations of the only two species of Kelloggia (Rubiaceae), which occur disjunctly in eastern Asia (K. chinensis Franch.) and western North America (K. galioides Torr.). The consistent mitotic prophase chromosome condensation pattern and interphase nuclei type were determined for both species. The chromosome base number of the genus is suggested to be x = 11. The karyotype of 2n = 22 = 2x = 16m + 6sm was examined for both species. The karyotypical asymmetry of 1A and 2A was found in K. chinensis and K. galioides, respectively. According to the predominant evolutionary direction of karyotype asymmetry in angiosperms, K. galioides (2A) seems slightly more evolved than K. chinensis (1A). Our finding is consistent with the hypothesis of the Old World origin of Kelloggia based on molecular study.

Monophyly of Kelloggia Torrey ex Benth. (Rubiaceae) and evolution of its intercontinental disjunction between western North America and eastern Asia.

Kelloggia Torrey ex Bentham (Rubiaceae) consists of two species disjunctly distributed in western North America (K. galioides Torrey) and the western part of eastern Asia (K. chinensis Franch.). The two species exhibit a high level of morphological divergence. To test its monophyly and to infer its biogeographic history, we estimated the phylogeny of Kelloggia and its relatives from sequences of three chloroplast DNA regions (rbcL gene, atpB-rbcL spacer, and rps16 intron). The monophyly of Kelloggia was strongly supported, and it forms a sister relationship with the tribe Rubieae. The divergence time between the two disjunct species of Kelloggia was estimated to be 5.42 ± 2.32 million years ago (mya) using the penalized likelihood method based on rbcL sequence data with fossil calibration. Our result does not support the Madrean-Tethyan hypothesis, which assumes an earlier divergence time of 20-25 mya. Ancestral area analysis, as well as dispersal-vicariance (DIVA) analysis, suggests the Asian origin of Kelloggia and the importance of Eurasia in the diversification of its close relatives in the Rubieae-Theligoneae-Paederieae group. The intercontinental disjunction in Kelloggia is suggested to have evolved via long-distance dispersal from Asia into western North America.