Format: ORAL

Maurane Bourgouin1,2, Robert F. C. Naczi3, Simon Pesant1,2, tienne Lveill-Bourret1,2

1. Centre sur la biodiversité, University of Montreal, Montreal, Québec, Canada 2. Marie-Victorin Herbarium, University of Montreal, Montreal, Québec, Canada 3. New York Botanical Garden, New York, USA

The unusual ecological conditions provided by freshwater estuaries, namely, high rate of sedimentation of nutrient rich minerals, twice-daily tides, waves, and ice-scouring, have induced the evolution of a highly specialized flora containing several endemics. The origin of this flora appears to be recent, dating at most to the last deglaciation 10,000-12,000 years ago, which is probably the cause of relatively minor morphological differentiation of most of the endemic taxa. Unfortunately, freshwater estuaries also are heavily urbanized and industrialized, contributing to habitat degradation and loss. Endemic Bidens taxa are an important component of the freshwater estuaries of Northeastern America and offer a great insight into understanding the recent evolution of the North American estuarine flora. Many of these endemics are hypothesized to have originated from hybridization and polyploidization (allopolyploidy). Unfortunately, taxonomic uncertainties of many of the Bidens taxa of Northeastern America are hampering conservation action. For instance, unclear morphological limits between species frequently result in misidentifications, which can lead to over- or under-estimation of the frequency of threatened taxa. We conducted a morphometric analysis to test species delineation, explore the relevance of new traits for identification, and test hybridization hypotheses. Most of the dissimilarity between species is correlated to flower and fruit traits, while vegetative characters show great lability that is largely uncorrelated with taxonomic boundaries except for species with composed leaf. We have obtain clear delineation between B. eatonii and B. infirma and between B. tripartita and B. comosa, species for which taxonomic status until this day were still uncertain. Even though more sampling is needed to better assess the full range of phenotypic variation of each species, the recognition of B. infirma, an endemic of the St-Lawrence estuary, Canada, would have a great impact on conservation action.