Towards resolving the evolutionary history of Caucasian pears (Pyrus, Rosaceae)—Phylogenetic relationships, divergence times and leaf trait evolution

Abstract

With approximately 25 endemic species, the genus Pyrus (pears) is highly diverse in the Caucasus ecoregion. The majority of Caucasian pears inhabit xerophytic open woodlands or similar habitats, to which they display morphological adaptations, such as narrow leaves. The other species, both Caucasian and non-Caucasian taxa, mainly inhabit mesophytic forests and display broad leaves. Using a representative taxon sampling of Pyrus from the Caucasus, Europe and Asia, we reconstruct phylogenetic relationships in the genus based on multiple plastid regions. We also estimate the divergence times of major clades in Pyrus, reconstruct the evolution of leaf shapes, and discuss the emergence of xeromorphic leaf traits. Our results confirm the monophyly of Pyrus and the existence of two major clades: (a) an E Asian clade with a crown group age of 15.7 (24.02-8.37 95% HPD) My, and (b) a W Eurasian clade that comprises species from Europe, SW Asia and the Caucasus and that displays a slightly younger crown group of 12.38 (19.02-6.41 95% HPD) My. The existing infrageneric classification of Pyrus was found partially incongruent with the inferred phylogenetic trees. Several currently accepted species were not recovered as monophyletic, indicating that current species limits require re-evaluation. Ancestral character state reconstructions revealed several independent transitions from broad-to narrow-shaped leaves in Pyrus, probably via intermediateshaped leaves.

Taxonomic and biogeographic notes on the genus Pyrus L. (Rosaceae): a new record and a new synonym, with data on seed morphology

“…Pyrus taxa are divided into Occidental and Oriental pears in accordance with geographical distribution [Bailey, 1917] and this was also confirmed by later phylogenetic studies [Korotkova et al, 2018]. Occidental taxa are distributed in Europe, North Africa, Turkey, Iran, Central Asia and Afghanistan, while oriental pears are widespread in East Asia.…”

Sex and Rosaceae apomicts

“…Others (e.g., Grevtzova, 1978) have similarly associated the production of unreduced female gametophytes with hybridization. Recent phylogenetic analyses of Pyrus (Zheng & al., 2014;Korotkova & al., 2017;Wu & al., 2018) refer to variation in ploidy level, and especially hybridization, as underlying the complexity of species-level taxonomy in this genus. Zheng & al.…”

Wild Pears of Armenia

“…They are distributed in temperate Eurasia, reaching the Atlas Mountains in North Africa as well as Japan and South China. The centers of diversity for Pyrus are in the mountainous regions of East Asia, the Mediterranean, and South-West Asia, including the Caucasus (Korotkova et al 2018).…”