This paper studies the floristic elements in seed plants from families to species in dry-hot valleys in Yunnan and Sichuan. There are 1707 species for statistics and analyses, which belong to 752 genera and 165 families.The results showed that most of the families are subtropical with the exception of world-wide species, and then less are warm-temperate and tropical. There are 27 tropical families, greatly more than those in dry-warm valley. At genus level, the number of tropical genus is significantly the ...