Floral Initiation and Development in Relation to the Time of Flowering in Banksia coccinea R.Br and B. menziesii R.Br (Proteaceae)

Abstract

Floral initiation and development in Banksia coccinea and B. menziesii were investigated using scanning electron microscopy in relation to the time of flowering. Floral initiation in both species occurred in late spring. The sequence of floral development was similar for both species but the timing was different. Ten stages of floral development were identified. Stage 1 was a vegetative meristem. Stage 2 signified the transition to the reproductive state, and was characterised by a broadening of the meristem with the production of involucral bracts. There were increases in both height and diameter of the meristem as common bracts (stage 3), floral bracts (stage 4) and florets (stage 5) were initiated. At stage 6 the developing inflorescences were macroscopically visible. This was followed by appearance (stage 7) and subsequent extension of the florets (stage 8). The styles continued to extend once floret extension had ceased causing the perianth to split and the styles to protrude (stage 9), thus imparting to the inflorescences their characteristic colour. Anther dehiscence occurred prior to anthesis of the floret, and the pollen was deposited on the pollen presenter, a distal modified region of the style. At anthesis (stage 10) styles were released from the perianth limb, presenting pollen to foraging insects and birds. Phyllotaxy was spiral throughout development, with a transition from a single genetic spiral in the vegetative shoot to 13 spirals initiating simultaneously in the developing inflorescence. Floral development was slow, taking from 6 to 8 months in B. menziesii prior to peak anthesis between April and July. In B. coccinea macroscopic inflorescences were not observed until May, with peak anthesis occurring between August and November, 9-12 months after initiation. Inflorescence colour showed wide variation in both species, with red and pink being the dominant colours in B. coccinea and B. menziesii respectively.