Pollination of the red hot poker Kniphofia caulescens by short-billed opportunistic avian nectarivores

Abstract

Recent studies indicate that short-billed birds which visit flowers opportunistically for nectar are important pollinators of African plants and select for floral characteristics which are distinct from those found in sunbird-pollinated species. Here we report the existence of a pollination system involving opportunistic nectarivores in Kniphofia caulescens, a high altitude member of a genus previously considered to contain only sunbird- and insect-adapted pollination systems. Plants of K. caulescens set approximately twice as many fruits and produced more seeds per fruit when exposed to both bird and insect pollination than to just insect pollination. Controlled pollination experiments showed that the species is genetically self-incompatible and thus totally reliant on pollinator visits for seed set. Opportunistic nectar-feeding birds appear to be the most important pollinators of this plant. In particular, Drakensberg Siskins ( Crithagra symonsi) and Yellow Canaries ( Crithagra flaviventris) were the most frequent visitors and carried the highest pollen loads. The Malachite Sunbird ( Nectarinia famosa), although often feeding on Kniphofia caulescens, carried very little pollen, presumably on account of its long bill which reduces contact between the floral anthers and its head feathers. Honey bees were also frequent flower visitors and made a secondary contribution to fruit set. Flowers of K. caulescens contained copious amounts (c. 30 µl) of very dilute (c. 9%) hexose-rich nectar which is consistent with the pollination syndrome found in plants pollinated by opportunistic avian nectarivores.