• (a.) Exhibiting a downward convexity caused by unequal growth. Cf. Epinastic.
Hy`po·nas'tic adjective [ Prefix hypo- + Greek ... pressed close.] (Botany) Exhibiting a downward convexity caused by unequal growth. Confer Epinastic . 
hyponastic An organ that curves upwards because the ventral surface grows more rapidly.