Reproductive biology of tree lucerne (Chamaecytisus palmensis, Leguminosae)

Abstract

The reproductive biology of tree lucerne or tagasaste, Chamaecytisus palmensis (Leguminosae), was investigated for two populations, one naturalised and one cultivated, on the Port Hills, Canterbury. The populations flowered in late winter and spring. The numerous white flag blossoms contained nectar and were visited by a variety of insects, but only bumble-bees were effective in operating the flowers: both bumble-bees and honey bees rob the flowers of nectar through the calyx but this does not usually directly damage the ovary. Self-pollination was recorded at the late bud stage and pollen germinated on the stigmas and penetrated the styles of these unvisited, untripped flowers. The species is self-compatible. Under open pollination, fruit production varied from 4 to 55% for individual trees. Although many ovules began to develop into seeds, abortion reduced seed production per pod to about 50% for both populations. Within pods, ovules at distal positions more often developed into seeds. Of the ovules available to be fertilized at flowering only 5% for the naturalised population and 16% for the cultivated population, developed into seeds. The difference between the two populations was largely a result of a difference in the proportion of flowers setting fruit rather than in seed production per pod.

Keywords:

• tree lucerne
• tagasaste
• Chamaecytisus palmensis
• Leguminosae
• reproductive biology
• pollination
• fruit production
• seed production
• fruit abortion
• seed abortion
• tree crops