Hybridization and long‐distance colonization in oat‐like grasses of South and East Asia, including an amended circumscription of Helictotrichon and the description of the new genus Tzveleviochloa (Poaceae)

Abstract

AbstractThe phylogenetic relationships of 31 genera of the traditional grass tribe Aveneae, with focus on Southeast Asian species of Helictotrichon, were examined using DNA sequences of the plastid matK‐psbA region, nuclear ITS, the nuclear single‐copy gene topoisomerase 6 (Topo6) spanning two introns and morphology. A molecular phylogenetic analysis was performed for 121 species applying maximum parsimony and Bayesian methods. Additionally we surveyed 11 Southeast Asian taxa for structural spikelet characters including lemmas, lodicules and ovaries. The phylogenetic results of the three molecular markers revealed that several Southeast Asian species traditionally accommodated in Helictotrichon are misplaced in this genus except for H. abietetorum, H. hideoi and H. leianthum. The placement of H. polyneurum and H. sumatrense in the genus Helictotrichon requires further investigation as suggested by morphological and preliminary molecular data. Due to the occurrence of different sequence types of ITS and Topo6, both nuclear DNA markers suggested an allopolyploid origin for several Southeast Asian taxa. (1) In Helictotrichon parviflorum and H. potaninii two different sequence types of Topo6 occur, closely similar to those of Trisetum and Helictotrichon, respectively. Nuclear ITS data of both species point to affinities with Trisetum and related genera but not to Helictotrichon. Both species belong to a hitherto unknown genus that is morphologically distinct from Trisetum and Helictotrichon and is named Tzveleviochloa. (2) Two copy types (A and B) of Topo6 previously identified in African Trisetopsis, a genus encompassing predominantly sub‐Saharan species that traditionally had been ascribed to Helictotrichon, also occur in two Southeast Asian species, i.e., H. junghuhnii and H. virescens. In agreement with morphological data both species need to be transferred to Trisetopsis. This expands the hitherto known eastern edge of the range of Trisetopsis from the Arabian Peninsula to China. (3) Additionally, the Chinese H. altius has a copy type sequence of Topo6 similar to that of Trisetopsis but not of Helictotrichon in its genome, whereas its plastid DNA fits Helictotrichon and relatives. Along with morphological characters this supports intermediacy between Trisetopsis and Helictotrichon. Therefore H. altius is probably an intergeneric hybrid, here named ×Trisetopsotrichon altius. The taxonomically difficult genus Helictotrichon s.l. in tropical to temperate southeastern Asia becomes disassembled into Helictotrichon s.str., the new genus Tzveleviochloa, gen. nov., and the nothogenus ×Trisetopsotrichon, nothogen. nov. The following combinations are introduced: Trisetopsis aspera, comb. nov., T. junghuhnii, comb. nov., T. virescens, comb. nov., ×Trisetopsotrichon altius, comb. nov., Tzveleviochloa burmanica, comb. nov., T. parviflora, comb. nov., T. potaninii, comb. nov.