Data from: Does the Platanthera dilatata (Orchidaceae) complex contain cryptic species or continuously variable populations?

Floral phenotypic traits are expected to reflect evolutionary changes and
are used as a reliable basis for species delimitation. However, when
traits overlap among populations of newly emerging species, this confounds
identification of evolutionarily distinct lineages and reduces taxonomic
stability. In this study, we quantified variation in ten floral traits and
plastid DNA sequences across 26 populations of Platanthera dilatata
(Orchidaceae) in North America to determine geographic structure among
populations and to evaluate support for three varieties recognized in the
current taxonomy. k-means clustering analysis, in the absence of a priori
designation of groups, indicated two morphologically distinct groups. Spur
length was the most distinctive character between groups. The group
containing larger flowers with longer spurs corresponds to the var.
leucostachys and most samples in this group are from western North
America. The vars. albiflora and dilatata could not be distinguished
within the second group, which exhibited flowers with short to
intermediate spurs and include samples from eastern and western North
America. Morphological variation in P. dilatata may reflect
pollinator-mediated selection, particularly in spur length, which is known
to vary in association with pollinators across Platanthera. Significant
genetic divergence was observed between the two groups (F ST = 0.15; P ≤
0.001), but we did not find corresponding phylogenetic structure, which
may reflect recent divergence and retention of ancestral polymorphisms.
Based on these results, we suggest preserving the current intraspecific
taxonomy until further studies determine the origin of floral variation
and the extent of gene flow between morphologically divergent populations.