Morphological and anatomical development in the Vitaceae. II. Floral development in Vitis riparia

Abstract

The anatomy, morphology, and ontogeny of the flowers of Vitis riparia are presented in this paper. The inflorescence is initiated as an uncommitted primordium, which in turn initiates a bract and then bifurcates to form inner and outer "arms." Both of the arms initiate inflorescence branches, first in a decussate pattern, then in a 2/5 phyllotactic spiral. These branches may initiate pairs of lateral primordia until a series of third- or fourth-order cymose inflorescence branches is initiated. Floral development begins when the calyx is initiated as three primordia, which first merge by meristem extension and then grow out to form an indistinctly five-toothed ring. The petals and stamens arise as five common primordia, alternating with the sepals. They divide into separate petal and stamen primordia. The gynoecium arises as a ring primordium. Two septae are initiated on the inner walls of the ring and grow together to form a two-loculed ovary. Two ovules arise from each septum. In male flowers the ovules form but do not mature, and the stigma and style fail to develop. The pollen is tricolporate. In female flowers the ovules are bitegmic and anatropous, the style is short, and the stigma is discoid or two parted. The pollen lacks furrows and pores. The yellowish disc arises from the base of the gynoecium and is more prominent in male flowers. The fruit is a one- to four-seeded bluish purple berry.