Floral ontogeny of Brunonia australis (Goodeniaceae) and Calandrinia sp. (Portulacaceae)

Abstract

Floral ontogeny of Brunonia australis Sm. ex R.Br. (blue pincushion) and Calandrinia sp. (not yet fully classified) was investigated by scanning electron microscopy to assist further efforts for manipulating flowering of these potential floriculture crops. This is the first work to study floral initiation and the stages of flower development for these species. Floral initiation of B. australis commenced 28 days after seed germination when grown at 25/10 or 35/20°C (day/night) under long days (11 h of ambient light at 553 ± 45 µmol m–2 s–1, plus a 5-h night break at <4.5 µmol m–2 s–1). Leaf number at floral initiation reflected differences in the accumulated thermal time between treatments so that about double the number of leaves formed at 35/20°C. This suggested differing temperature responses for leaf and phenological development, and that leaf number was not a good indicator of floral initiation. For Calandrinia sp., floral initiation commenced 47 days after seed germination when grown at 25/10°C. Hot temperatures (35/20°C) inhibited flowering; indicating a vernalisation requirement. For B. australis, the pattern of floret development was centripetal, with flowers organised into five whorls. Four bracts surrounded each flower, whereas the sepals, petals and stamens showed a pentamerous arrangement. A central style was terminated by an indusial stigmatic presenter. Flowers of Calandrinia sp. consisted of four whorls, namely two sepals, 8–10 petals, numerous stamens produced centrifugally and a central syncarpous gynoecium with four stigmatic branches.