Flora of seed plants in pastures of the Sunan and Subei County

We investigated the distribution and species of grassland plants in Sunan and Subei county which are located along the northwest end of the Qilian Mountain – Hexi Corridor in Gansu Province. The results show that the region is rich in grassland plant species and includes a total 376 vascular plant species belonging to 178 genera and 53 families. These plants consist of one fern species, seven gymnosperm species (from four genera in three families), and 368 angiosperm species (from 173 genera in 49 families). Thus, regional grassland vegetation is mainly composed of seed plants (gymnosperm and angiosperm). The five largest plant families are Asteraceae (59 species), Poaceae (57 species), Fabaceae (35 species), Chenopodiaceae (26 species), and Cyperaceae (20 species), and they account for 9.4%, 39.6%, and 51.1% of the total families, genera and species in the region, respectively. These families are thus considered to dominate the regional grassland vegetation. Moreover, the proportion of single-species families in this region is as high as 41.5%. Along with the low ratios of species to genera (2.11) and species to families (7.09), this finding suggests high regional floristic diversity. Based on the family-level analyses, 52 investigated seed plant families are divided into 5 areal types and 5 subtypes. The proportion of the widespread family type is highest and accounts for 57.7% of the total regional family number. The temperate and tropical family types are regional sub-dominant families and account for 26.9% and 11.5% of the total families, respectively. At the genus level, 177 investigated seed plant genera are divided into 9 areal types and 15 subtypes. The genera with a significant temperate component are absolutely dominant and account for 57.9% of the total regional genus number. Genera with Mediterranean components and Central Asian components are sub-dominant and account for 10.7% and 6.2% of the total genera, respectively. In contrast, genera with West Asian, East Asian, and tropic components are sparse. The above results indicated that the floristic characteristics of the region are in line with the characteristics of arid areas in Northwest China.