Flowering phenology of Nouelia insignis

Nouelia insignis Franch (Asteraceae) is a short, narrow endemic
and endangered tree, growing with a natural population in the dry and hot
valley of the Jinsha River in the southwest area of China. In this work,
flowering phenology (time and duration), floral biology, visit frequency
and behavior of pollinators, and pollination characteristics were studied
based on investigation in the field and analysis in the laboratory with
the help of a stereomicroscope, and the relationship between seed setting
rate and reproductive traits, as well as the relationship between
flowering time and rainfall before flowering was tested using the method
of general linear regression model. The results showed that natural
population of N. insignis exhibited high flowering synchrony with
relatively stable flowering duration, and the flowering time fluctuated
greatly depending on the rainfall 5 months before flowering. The
pollination of N. insignis required pollinators, and insect activities
played a very important role in the pollination process. However, lack of
the pollinators was not a limitation for reproductive fitness in N.
insignis, although the number of pollinators was small and the frequency
of visits was low. In addition, no pollen limitation was found during
pollination. The average seed setting rate of N. insignis in the natural
condition was only 1.52%–3.73%, and it was generally affected by changes
in flowering phenology between years, and had a higher seed set in early
flowering year. The annual variation of seed set might be related to the
annual variations of stamen and pistil functions, such as changes of
pollen viability and stigma receptivity, which were closely related to
flowering time. The results of this study are of value for further
conservation actions on natural population of this threatened endemic
plant.