Floristic and Phylogenetic Characteristics of Seed Plants in Typical Danxia Landforms of Northern Guizhou

This study investigated the seed flora composition, phylogenetic structure, and spatial differentiation patterns in typical Danxia landforms, northern Guizhou. It provided a scientific basis for understanding the biodiversity formation mechanisms and conservation in this region. Through systematic plot surveys, specimen identification, and literature compilation, a seed plant checklist was produced. The study combined floristic geographic and phylogenetic analyses to explore the flora composition, geographic components, phylogenetic structure, and phylogenetic diversity (PD) of seed plants, comparing them with the adjacent karst and non-karst landforms. The results indicated that: A total of 1,65 A total of 165 families, 779 genera, and 2,055 species of seed plants are present in the study area. Among them, 46 species are nationally protected (2 species at National Level I and 44 species at Level II), and 13 species are endemic to China. The floristic geographic components are complex and diverse. At the family level, the predominant distribution types are the pantropical type (34.71%) and the northern temperate type (10.74%). At the genus level, the ratio of tropical (49.86%) to temperate (50.14%) components is nearly equal, reflecting the typical subtropical montane transitional floristic characteristics. Phylogenetic structure analysis showed that most of the plots have negative values for net phylogenetic distance (NRI) and net nearest taxon index (NTI), indicating phylogenetic divergence. About 62.86% of the plots have NRI < 0 and 74.29% have NTI < 0, suggesting that the species in the communities are phylogenetically more distant than randomly expected. A few plots exhibited positive NRI and NTI values, showing phylogenetic clustering. Compared to the neighboring karst and normal landforms, the Danxia landform has a lower total phylogenetic diversity (PD = 32,471.24). Despite similar species richness, it accumulated shorter evolutionary branch lengths. The unique red sandstone and gravel geological structure of northern Guizhou Danxia landforms, combined with the transitional climate of the mid-subtropical zone, shapes its flora with both tropical affinity and temperate characteristics. The community phylogeny generally exhibited a divergent pattern, suggesting that diffusion limitations or stochastic processes may play an important role in community assembly in highly heterogeneous habitats, while the effect of specific habitat filtering cannot be ruled out. Different landforms nurture significant distinctiveness in plant communities, highlighting the unique value of Danxia landforms in the regional biodiversity pattern.