Nectar sugars in Proteaceae: Patterns and processes

The nectar sugar composition is presented for 147 species from 16 genera of South African and Australian Proteaceae. Patterns associated with flower age, different plants and populations, plant phylogeny and pollination have been examined. In addition to the usual three nectar sugars (sucrose, fructose and glucose), the nectar of Protea and Faurea contains the pentose sugar xylose at concentrations of up to 39% of total sugar. Xylose has not previously been reported from floral nectar and is absent from the nectar of Adenanthos, Banksia, Brabejum, Dryandra, Grevillea, Hakea, Lambertia, Leucospemtum, Macadamia, Mimetes, Orothamnus, Paranomus, Stenocarpus and Telopea. Most genera and species have hexose-dominant nectar, but within the large genera Banksia, Grevillea, Leucospermum and Protea some of the seemingly more derived species have sucrose-dominant nectar. This interesting dichotomy of low versus high sucrose is of diagnostic value at the species level and indicative of phylogenetic relationships within the larger genera. At the generic level, the presence of xylose is a convincing synapomorphy for Protea and Faurea. Studies of physiological processes (e.g. enzyme activities) and ecological processes (e.g. pollination) may help to explain some of the conservative and taxonomically interesting nectar sugar patterns.