Inflorescence development in Amelanchier alnifolia

The morphology and development of the inflorescence of Amelanchier alnifolia, a potential fruit crop, are described. Although racemelike in appearance, the 8- to 12-flowered inflorescence is determinate, and the occasional branching of the basal member indicates its compound nature. This basal member in the axil of a foliage leaf frequently bears three to four bracteoles instead of the two characteristic of the remaining lateral flowers, and an arrested bud may be found in the axil of one or more of the bracteoles. The inflorescence is thus interpreted as a much reduced panicle. The phenology of inflorescence development in relation to seasonal shoot growth has been documented. Transformation of vegetative shoot apices to the flowering condition begins after the differentiation of a set of cataphylls and as the current fruit crop is ripening. It is marked by the accelerated formation of bract primordia with precocious axillary buds, culminating after about 2 weeks with the initiation of a terminal flower. Although the last to be formed, the terminal flower at all subsequent stages is equivalent in development to those at the base of the inflorescence. The buds in the axils of three to five bracts immediately below the terminal flower are arrested at an early stage and variation in inflorescence size may in part be due to variability in their development.