Data from: Morphological, molecular, and ecological divergence in Pinus douglasiana and P. maximinoi

Pinus douglasiana and P. maximinoi (Pinus subsection Ponderosae) are
closely-related New World pines with vague taxonomic boundaries where
their natural ranges overlap in western Mexico. They are distinguished
from each other by the width of their leaves and thickness of their cone
scale apophyses. They are also sometimes confused with two other close
relatives, Pinus pseudostrobus and P. yecorensis. We integrated
morphological, molecular, and ecological data to clarify the taxonomic
limits among these four species. Following previous studies, we evaluated
16 quantitative leaf and seed cone characters. Pinus douglasiana, P.
maximinoi, and P. pseudostrobus formed non-discrete groups in multivariate
space. The absence of leaf hypodermal intrusions, a persistent peduncle,
and the shape of the seed cone are useful for differentiating P.
pseudostrobus and P. yecorensis from P. douglasiana or P. maximinoi, and
the latter two can usually be distinguished by needle width or cone scale
apophysis thickness. Most individuals identified as P. douglasiana, and P.
maximinoi shared haplotypes for a plastid ycf1 fragment that is relatively
variable for the genus, while P. yecorensis has a closely related,
exclusive haplotype. A distinct haplogroup included all individuals of P.
pseudostrobus and the remaining individuals of P. douglasiana and P.
maximinoi. Leaf width and cone scale thickness of P. douglasiana and P.
maximinoi are correlated with elevation. According to potential
distribution models, P. yecorensis is distributed in drier areas than P.
douglasiana or P. maximinoi, while P. pseudostrobus occurs in more
temperate areas, commonly at higher elevations. Pinus douglasiana and P.
maximinoi can be considered as incipient species undergoing divergent
evolution characterized by incomplete morphological, molecular, and
ecological divergence.