East Asian origin and Northern Hemisphere diversification in the Brachythecium novae‐angliae‐complex (Bryophyta)

Abstract

AbstractCool climate biomes in the Northern Hemisphere have evolved relatively recently. Temperature decline between the late Eocene and the Pliocene contributed to the evolution of many plant groups in modern cool climate biomes, such as mosses belonging to the Brachythecium novae‐angliae‐complex. The Brachythecium novae‐angliae‐complex comprises three species that have a disjunct distribution in temperate and boreal regions in the Northern Hemisphere. The core species in the complex have only recently been transferred from Bryhnia to Brachythecium and the delimitation of the complex and of species within it still remains uncertain. We reconstructed the evolutionary history of the group using molecular data and estimated the timing of the diversifications in the tree. In addition, we examined the morphology and compared morphological diversification with genetic diversity. The Brachythecium novae‐angliae‐complex diversified in East Asia in the middle Miocene, 9.1 Ma (HPD 95% 3.9–14.8 Myr). Bryhnia trichomitria and B. graminicolor were revealed not to be close relatives of the complex and are therefore transferred to Brachythecium and Koponeniella gen. nov., respectively. Both morphology and molecular data supported the position of Asian Brachythecium noesicum as sister to the Brachythecium novae‐angliae crown clade that includes two species, B. hultenii and B. novae‐angliae. The crown clade diverged at the end of the Miocene, 6.4 Ma (HPD 95% 2.4–11.6 Myr) and its taxa have a disjunct distribution in cool temperate and boreal areas in the Beringia region (B. novae‐angliae subsp. hultenii), and eastern North America and northwestern Europe (B. novae‐angliae subsp. novae‐angliae). In the crown clade the majority of populations belong to one common haplotype present in all three disjunct parts of the distribution area. Despite low variation in DNA sequence data, morphology allows the distinction between B. novae‐angliae subsp. hultenii and B. novae‐angliae subsp. novae‐angliae. Because of weak morphological and genetic differentiation, European Bryhnia scabrida is treated here as a synonym of Brachythecium novae‐angliae subsp. novae‐angliae. Glacial survival during the Quaternary and climatic oscillations during the late Tertiary and Quaternary in East Asia may have resulted in diversification of the complex and enabled adaptation to cool temperate and boreal climates.