We introduce a condition on accretive matrix functions, called p-ellipticity, and discuss its applications to the L p theory of elliptic PDE with complex coefficients. Our examples are: (i) generalized convexity of power functions (Bellman functions), (ii) dimension-free bilinear embeddings, (iii) L p -contractivity of semigroups, and (iv) holomorphic functional calculus. Recent work by Dindoš and Pipher established close ties between p-ellipticity and (v) regularity theory of elliptic PDE with complex coefficients. The p-ellipticity condition arises from studying uniform positivity of a quadratic form associated with the matrix in question on one hand, and the Hessian of a power function on the other. Our results regarding contractivity extend earlier theorems by Cialdea and Maz'ya.