Chin J Plan Ecolo ›› 2015, Vol. 39 ›› Issue (7): 753-761.DOI: 10.17521/cjpe.2015.0072

• Orginal Article • Previous Articles     Next Articles

Floral morphology and pollination mechanism of Salvia liguliloba, a narrow endemic species with degraded lever-like stamens

HUANG Yan-Bo1, WEI Yu-Kun1,*(), WANG Qi1, XIAO Yue-E1, YE Xi-Yang2   

  1. 1Shanghai Chenshan Botanical Garden, Shanghai Chenshan Plant Science Research Center, Chinese Academy of Sciences, Shanghai 201602, China
    2Zhejiang A&F University, Hangzhou 311300, China
  • Online:2015-07-01 Published:2015-07-22
  • Contact: Yu-Kun WEI
  • About author:

    # Co-first authors

Abstract: Aims Diverse stamen structures and interactions with pollinators make Salvia the model plants for studying evolutionary changes in plant pollination mechanisms. The dorsal pollination mechanism of lever-like stamens has been extensively investigated as a classic example for precise interactions between plants of Salvia genus and their pollinators. However, there are many atypical lever-like structures and pollination mechanisms among Salvia species. For example, Salvia liguliloba has floral organ structures and a pollination mechanism characterized by degenerated lever-like stamens. The aim of this work was to understand the selection pressure and ecological significance of Salvia plants that have the atypical staminal level mechanism. Methods In this study, we described the morphological features of S. liguliloba, a plant species endemic to the Tianmu Mountains, and investigated its pollination ecology in detail. Various components of the flower of S. liguliloba were measured, which included the corolla, corolla tube, corolla entrance, filament, connective and pistil. Flower-visiting insects, pollinators, and the pollination process were observed and recorded by a digital video camera. Furthermore, we focused on comparing the floral organ structures and the pollination characteristics of S. liguliloba with those of S. digitaloides, which has a short-lever stamen. The relative frequency of insects, visiting time per flower, activity rate and visitation rate were measured and compared with the data from our previous study of S. digitaloides, for which the flower structure and pollination features were well concluded. Important findings Salvia liguliloba has smaller corolla length, tube width, and shorter filament and pistil than S. digitaloides (p < 0.05). The only effective pollinator was Bombus trifasciatus, and its average relative visiting frequency and the visiting time per flower were (0.959 ± 0.065) and (1.54 ± 0.60) s. The degenerated lower arm and limited moving space in the upper arm of the stamen restrict the pollinating insects from pushing the stamens in a lever-like motion. Thus, bumblebees completed pollination with the aid of their heads. Compared with the structure of the lever-like stamen and the pollination mechanism of S. digitaloides, the structural features of the floral organs of S. liguliloba make it adapt to a more specific pollinator with shorter visiting time and higher activity rate. The results suggested that the species with degraded lever-like stamens might be different from other typical Salvia species in their evolution direction and reproductive strategy.

Key words: adaptive evolution, forehead pollination, short-lever stamen, Salvia liguliloba, Bombus trifasciatus