Gynoecial pathway for pollen tube growth in the genus Monotropa

The gynoecial micromorphologies of Monotropa uniflora and M. hypopitys are compared to characterize the gynoecial pathway for pollen tube growth. The receptive surface of the concave stigma is restricted to a papillate rim coated with an exudate. An internal transmitting tissue in the stigma joins the papillae with an external transmitting tissue system formed by the lining of the fluted stylar canal that may limit pollen tube growth to specific ovule-bearing placentae. Consequently, pollen tube growth is facilitated in the vicinity of the ovular micropyles.