Floral development of dioecious species and trends of floral evolution inPiper sensu lato

Abstract

The initiation of the floral parts (mainly stamens and carpels) is described for the four dioecious species ofPiper: Piper polysyphorumC. DC.,P. bavinumC. DC.,P. pedicellatumC. DC.,P. pubicatulumC. DC. The initiation order resembles that in the perfect flowers of some species, such asP. amalago. The carpels are initiated simultaneously, in most cases, as three primordia. InP. polysyphorum, carpel tips split into two lobes, so that finally a four- or five-lobed stigma will be formed when the ovary is fully developed. The staminodes (exactly, staminodial primordia) in the female flowers are initiated in the same order as the stamens in the male flowers and remain until the ovaries are enclosed. The unisexual flowers have stamens reduced to three or two. The reduction of stamen or staminode (staminodial primordium) number is accompanied by the change of their positions from opposite the carpels to alternate. After the initiation of the staminodes, or, exactly staminodial primordia, in the female flowers, the central part of the floral apex forms a ring meristem which is triangular. The carpel primordia (often three) are initiated on the three points of the ring meristem. The evolutionary trends of the flowers ofPiper sensu latoare discussed.