Floral ontogeny of Swainsona formosa (Fabaceae: Faboideae: Galegeae)

Abstract

Swainsona formosa (G.Don) J.Thompson (Sturt’s desert pea) is used in commercial floriculture for cut flowers and ornamental pot plants; however, accurate identification of the growth stages is critically important in making management decisions in floricultural crops. This plant was investigated by stereomicroscopy and scanning electron microscopy (SEM) to identify flowering time and stages of floral development. This is the first work to describe the complete floral ontogeny in a member of tribe Galegeae. Conversion from vegetative to reproductive stages began within 40–46 days after seed germination for axillary branches and within 46–52 days for central stems. Plants required 807.5 days °C growing degree-days for axillary branches and 921.5 days °C for central stems to reach 50% flowering. The central stem grew more nodes (11.1 ± 0.97 nodes) before the initiation of the first flower than did the axillary branches (7.2 ± 0.93 nodes). The order of floral organ initiation within each whorl is unidirectional, except for the petal whorl, which is simultaneous; the flower is organised into five whorls and shows a pentamerous arrangement of sepals and petals, 10 stamens in two whorls and a central carpel.