Abstract
The North American endemic genus Penstemon (Mitchell) has a recent geologic origin of ca. 3.6 million years ago (MYA) during the Pliocene/Pleistocene transition and has undergone a rapid adaptive evolutionary radiation with ca. 285 species of perennial forbs and sub-shrubs. Penstemon is divided into six subgenera occupying all North American habitats including the Arctic tundra, Central American tropical forests, alpine meadows, arid deserts, and temperate grasslands. Due to the rapid rate of diversification and speciation, previous phylogenetic studies using individual and concatenated chloroplast sequences have failed to resolve many polytomic clades. We investigated the efficacy of utilizing the plastid genomes (plastomes) of 29 species in the Lamiales order, including five newly sequenced Penstemon plastomes, for analyzing phylogenetic relationships and resolving problematic clades. We compared whole-plastome based phylogenies to phylogenies based on individual gene sequences (matK, ndhF, psaA, psbA, rbcL, rpoC2, and rps2) and concatenated sequences. We also We found that our whole-plastome based phylogeny had higher nodal support than all other phylogenies, which suggests that it provides greater accuracy in describing the hierarchal relationships among taxa as compared to other methods. We found that the genus Penstemon forms a monophyletic clade sister to, but separate from, the Old World taxa of the Plantaginaceae family included in our study. Our whole-plastome based phylogeny also supports the rearrangement of the Scrophulariaceae family and improves resolution of major clades and genera of the Lamiales.
Highlights
The genus of Penstemon (Mitchell) is a large group of ca. 285 species of flowering plants endemic to North America [1,2,3]
The NOVOPlasty output log identified between 12,238,056 (P. palmeri) and 2,414,370 (P. rostriflorus) reads that aligned to the reference plastome sequence, assembled between 1,141,338 (P. palmeri) and 643,118 (P. rostriflorus), at an average organelle coverage of between 62,837 (P. personatus) and 16,203 (P. cyaneus) (Table 2)
The long single copy (LSC) lengths ranged from 84,217 bp (P. personatus) to 83,795 bp (P. palmeri)
Summary
The genus of Penstemon (Mitchell) is a large group of ca. 285 species of flowering plants endemic to North America [1,2,3]. The genus of Penstemon (Mitchell) is a large group of ca. 3.6 million years ago (MYA) [3]. Phylogenetic resolution and complete plastome sequences of Penstemon hypothesize the origin for Penstemon around the Pliocene/Pleistocene transition ca. This genus has extraordinary genetic and phenotypic diversity as evidenced by the array of ecosystems it inhabits and number of published taxa [4]. The rapid and recent diversification and speciation in Penstemon is associated with dramatic differences in diploid genome size ranging from 462 megabase pairs (Mbp) in P. dissectus to 922 Mbp in P. nitidus [5]. The rate of speciation, span in genome sizes, and relatively low mutation rate in plastome coding regions creates a unique challenge for systematists attempting to fully resolve phylogenetic relationships in Penstemon
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