Buddleja davidii and Buddleja yunnanensis: Exploring features associated with commonness and rarity in Buddleja

Buddleja davidii is a widespread shrub in Asia while B. yunnanensis is a narrowly endemic species limited to Yunnan Province, China. To explore whether floral volatiles, morphological characters of flower and seed and breeding system are correlated with their distributions, we measured length and width of corolla, trichome density at corolla throat, level of stigma/anthers relationship, seed size and weight. The results indicated that these characteristics were significantly different between the two species (P < 0.01). Bagging experiments revealed that B. davidii is a self-incompatible plant while B. yunnanensis is self-compatible. Thick trichome density at the corolla throat may reduce out-crossing in B. yunnanensis. Autogamy plays an important role in fruit production of this species while B. davidii requires pollinators for fruiting. Scents were collected using dynamic headspace adsorption method and identified with coupled gas chromatography and mass spectrometry. In total, 27 floral scent compounds were identified. The volatile composition in the two species was very different. We attempted to determine if these features, associated with commonness and with rarity found in these two taxa, could also help to explain the distribution pattern of other species of the genus Buddleja.