Each petal has its tip inflexed, giving it an obcordate appearance.
"Scientific American Supplement, No. 829, November 21, 1891" by Various
Obcordate: inversely heart-shaped, with the point applied to the base of another object or part.
"Explanation of Terms Used in Entomology" by John. B. Smith
Sometimes they are umbilicate below, so that a vertical section would be obcordate.
"The North American Slime-Moulds" by Thomas H. (Thomas Huston) MacBride
Pod many-seeded, obcordate-triangular, wingless.
"The Manual of the Botany of the Northern United States" by Asa Gray