An unusual kind of nectary in the oil flowers of Monttea: its structure and function

The presence of two rewarding systems, i.e. oils and nectar, is here considered in relation to the pollination biology and the pollinators of Monttea schickendantzii and M. chilensis are recorded for the first time.

Abstract

Monttea and Melosperma form the tribe Melospermeae, an endemic group of subtrobical South American Scrophulariaceae. All species of Monttea have trichome elaiophores that secrete oils which are collected by female solitary bees of the genus Centris equipped with special oil-collecting structures on their forelegs. The elaiophore is basically the same in the three Monttea species, though in M. schickendantzii and M. chilensis it is split into two areas and arranged in two shallow pouches. In addition to oils, these flowers secrete small quantities of nectar as an alternative reward. The form and nature of the nectar gland is unusual for the familiy and rare in flowering plants. Melosperma, which provides only nectar to its pollinators, shares with Monttea the same kind of nectary. It is derived from the base of the floral tube, corresponds anatomically to the mesenchymatic type, and persists after corolla abscission. The presence of two rewarding systems, i.e. oils and nectar, is here considered in relation to the pollination biology. The pollinators of Monttea schickendantzii and M. chilensis are recorded for the first time. The Monttea pollinators can have, in addition to the regular foreleg oil-collecting combs, specialized tarsal pads to collect oils from trichome elaiophores. Oil collecting organs are also present on the middle legs, though these are not used while foraging oils from Monttea.