Flowering phenology of co-occurring Asteraceae: a matter of climate, ecological interactions, plant attributes or of evolutionary relationships among species?

We analyzed the flowering phenodynamics of 43 Asteraceae species co-occurring in natural populations of Chaco Serrano forests in central Argentina. We explored the potential influence of factors such as photoperiod and climate (variations in temperature, rainfall, and frost), animal-plant interactions (richness of floral visitors, frequency of visits), some plant attributes (plant growth form, seed dispersal mechanism), and evolutionary relationships among species on flowering phenodynamics. Cluster Analysis (CA) and Principal Component Analysis (PCA) were the multivariate statistical methods used to analyze emerging patterns associated with these co-occurring species. Null-model analyses were used to evaluate whether flowering times are aggregated, segregated, or random. Results showed that flowering phenology was significantly correlated with the seasonal variation in temperature, photoperiod, rainfall, and frost. The multivariate statistical methods separated all the species in three groups: 1) species with short flowering time, large plant floral display, high frequency of visits by a large number of species of floral visitors, anemochorous fruits, and shrubby growth form, with a tendency to a segregated flowering pattern; 2) species with long flowering time, small plant floral display, low frequency of visits by few insect species, anemochorous fruits, and herbaceous growth form; and 3) species with long flowering time, small plant floral display, intermediate values for frequency of visits and number of species of floral visitors, seed dispersal mechanisms other than anemochory, and herbaceous growth form. In addition, all but one species belonging to early-branching tribes (tribes phylogenetically close to the root of the Asteraceae tree) were grouped together and clustered in the same region of the two-dimensional PCA ordination. All species belonging to the late-branching tribes (Asteroideae subfamily tribes) included in group 1 were separated from the other Asteroideae species in the PCA. In conclusion, it seems that climatic factors restrict the phenological period of most species, and that plant attributes and taxonomic membership are strongly related to flowering phenodynamics in this group of Asteraceae studied.