Rehmannia is a genus of seven species of flowering plants in the order Lamiales and family Orobanchaceae, endemic to China.

[2] It has been placed as the only member of the monotypic tribe Rehmannieae,[1][3] but molecular phylogenetic studies suggest that it forms a clade with Triaenophora.

Earlier molecular studies suggested that its closest relatives were the genera Lancea and Mazus,[6] which have been included in Phrymaceae.

[8] A 2016 classification of flowering plants, the APG IV system enlarged Orobanchaceae to include Rehmannia,[9] making it one of the few genera in the family, along with Lindenbergia, not to be parasitic.

[11] It is the main ingredient in a mixture called si wu tang (four substance decoction) along with Dang gui, Chinese peony (bai shao yao), and Ligusticum striatum (chuan xiong) that is considered a fundamental medicine to support making blood.