Phylogenetic pattern of alpine plants along latitude and longitude in Hengduan Mountains Region.

To detect the horizontal pattern of phylogenetic structure shown by alpine plants, we measured phylogenetic structure using net related index (NRI) and net nearest taxon index (NTI), and analyzed the phylogenetic structure patterns of alpine plants along longitude, latitude and environmental gradients in the Hengduan Mountains Region (HDMR). Our results show that: 1) the phylogenetic structure tended to cluster with increasing latitude and longitude; 2) for NRI, latitude was closer related than longitude, while for NTI, longitude was closer related than latitude, though they both not significantly relate to NTI. The phylogenetic structure tended towards overdispersion in the southern HDMR, with good climate conditions of higher mean annual temperature and more mean annual precipitation. In contrast, with harsh climate conditions of lower mean annual temperature and less mean annual precipitation, the increasing environmental stress led to phylogenetic clustering in the northern HDMR. The results highlighted that in the alpine region of HDMR, environmental filters and geographical isolation had a great effect on the latitudinal and longitudinal alpine species distribution, respectively.