Lima bean, Phaseolus lunatus cv. Early Thorogreen, is primarily self-pollinated. Morphological characteristics of reproductive structures which facilitate self-pollination include the stage of floral development at the time of anther dehiscence and the relative positions of anthers and stigma within the keel at the time of pollen shedding. Coincidental maturation of pollen and receptivity of the stigmatic surface also enhance the capacity for self-pollination. The varying degrees of cross-pollination frequently reported may be facilitated by extrusion of the stigma from the keel, which occurs in connection with insect visitation at an thesis, and also by the prolonged period of stigma receptivity, which extends from the white bud stage through anthesis.
The high degree of self-pollination in Phaseolus vulgaris cv. Light Red Kidney is attributed to the fact that flowers are autogamous and to the following characteristics: proximity of anthers and stigma at time of maturity; simultaneous maturation of pollen and receptivity of the stigamtic surface; and, possibly, to the position and orientation of stylar hairs. A morphologically variant pistil, in which the stigma is receptive when the flower is fully open, develops in a few flowers. Such flowers may be cross-pollinated by bees or other insects. The sugary secretion of stigmatic epidermal cells appears to enhance pollen retention and may provide an environment conducive to pollen germination.