Disentangling the Tillandsia capillaris complex: phylogenetic relationships and taxon boundaries in Andean populations

Abstract

We studied the genetic diversity and structure of the Tillandsia capillaris complex, a morphologically diverse group of highly specialized epiphytes, across the distribution range in arid mountain regions of central Peru,Chile, Bolivia and central Argentina. To elucidate the phylogenetic relationships in the complex and to explore the taxon boundaries among populations, we used three plastid markers (rpoB-trnC-petN, trnK-matK-trnK, ycf1,c. 8100 bp in total) and one single-copy nuclear gene (PHYC, c. 1200 bp) for 69 populations and 96 individuals ofthe T. capillaris complex plus 16 outgroup taxa. Bayesian inference of plastid DNA data indicates the existence of two evolutionary core lineages, which can be recognized as two distinct species: T. capillaris and T. virescens(as proposed previously on the basis of morphological characters). Tillandsia capillaris is a monophyletic and homogeneous group, widely distributed and less genetically variable, whereas T. virescens (including T. kuehhasii) is genetically more divergent with most of the forms growing at high elevation in arid areas, except for the small clade including T. virescens s.s.(= T. cordobensis), which grows in lower, more humid habitats. The nuclear analysis resulted in a polytomy with some individuals showing incongruent positions between plastid and nuclear topologies. The high haplotype diversity, consisting of 63 plastid DNA haplotypes in 69 populations, was resolved as two core lineages occurring from north to south, allowing us to establish a preliminary view of the genetic variation overlapping between the two taxa. The results suggest that the genetic differentiation into two main clades is consistent with morphological variation in this Andean complex.