The Hainan Island has the most extensive and well-preserved tropical forests in China. With rapid economic development of Hainan, biodiversity is increasingly at risk. Determining the spatial patterns of plant diversity in Hainan and explaining the drivers behind plant diversity are important considerations in assessing and maximizing the effectiveness of national parks, such as the newly designated Hainan Rainforest National Park. We assessed phylogenetic diversity patterns, and species richness using 106,252 georeferenced specimen records and a molecular phylogeny of 3,792 native plant species. Based on phylogenetic range-weighted turnover metrics, we divided the Hainan flora into four major floristic units. The Grade of Membership model was used to further verify the four units and to understand their boundaries and the internal structure of each floristic unit. Finally, the best combination model was used to explore the driving mechanisms underlying the division. Our results reveal that central Hainan is the most important hotspot for plant endemism and diversity, followed by the southern. Environmental energy is the main factor determining the spatial patterns of native plant diversity on the island, and accessibility has the greatest impact on native plant diversity among social factors. We explore patterns of spatial phylogenetics and biogeography to identify potential priorities for management and conservation drivers of plant diversity patterns across Hainan, to provide the basis for the effective protection of native plant diversity and the improvement of national parks of Hainan Island.

In order to determine the taxonomic composition of Hainan's native plants, we compiled a list of 5,860 native plant species belonging to 285 families and 1,875 genera based on the plant species lists of Xing et al. (2012) and Yang et al. (2016). We then screened and removed exotic cultivated plants, exotic escaped plants and naturalized plants using checklists, and combined subspecies and variants at the standard taxon species level. In total, we identified 3,792 native plants belonging to 257 families and 1,804 genera, representing 64.71% of the total plant species, 96.21% of the total plant genera and 90.18% of the total plant families present on the island. On this basis, we have compiled a list of 93 recorded endemic species by referring to the Hainan Endemic Plant Directory.

For locality information, we combined the geolocations of specimens from Xing et al. (2012) and Yang et al. (2016) with the National Specimen Information Infrastructure (NSII; www.nsii.org.cn), the China Plants Database (DCP; http://db.kib.ac.cn). We removed all occurrence records with latitude and longitude values ​​of "0" or "NA", and divided the coordinate records into two categories: Hainan Island and Chinese Mainland.

We used five loci to reconstruct the phylogeny: the nuclear internal transcribed spacer (ITS) and the chloroplast loci trnL, matK, ndhF, and rbcL. We extracted gene sequences from GenBank (Benson et al., 2017) following the methodology of Smith et al. (2011). We conducted a maximum-likelihood phylogenetic analysis (ML) in RAxML (Stamatakis, 2006) HPC2 within the CIPRES (Miller et al., 2010) Portal on XSEDE. We performed 1,000 bootstrap replicates with automatic termination (i.e., -l autoFC) (Zhu et al., 2021). We then used Figtree 1.4.4 (Zhu et al., 2021) to visualize the resulting topology and export the tree in Newick format.