Flower characteristics and visitors of Merremia macrocalyx (Convolvulaceae) in the Chapada Diamantina, Bahia, Brazil

Abstract

Merremia macrocalyx (Ruiz & Pav.) O’ Donell (Convolvulaceae) is a common, native herb in open grasslands (Campos Gerais) of northeastern Brazil. At Pai Inácio Mountain, Chapada Diamantina, Bahia, Brazil (12º 27´41”S, 41º 28’ 34”W), we made daily observations from 6:30 a.m. until 5:30 p.m. from 25 April to 29 April, 2003 and on May 31, 2005. The stereomorphic corolla of the weakly scented flowers was 4.04 mm mean diameter, tube depth was 3.12 mm, and the mean diameter of the gullet was 1.17 mm. Anthesis is diurnal, between 06:30 a.m. and 07:45 a.m. and floral longevity varied between 9-10 h. Nectar secretion occurred from 7:00 a.m. to 11:00 a.m., and the standing crop of nectar per flower increased from 0.67 ml (7:00 a.m.) to 2.5 ml (09:00 a.m.) then declining. The nectar sugar concentration was low (22%). Bees were the most frequent visitors, and were classified into six morpho-functional categories. Their daily foraging pattern was synchronized with nectar availability, being concentrated between 8:30 and 10:30 a.m. The clumped distribution of the plants, flower size and easily accessible nectar all stimulate visitation, especially by generalist bee species. Eusocial bees (A. mellifera, Geotrigona mombuca and Bombus morio) and the solitary bee Euplusia nigrohirta (Friese, 1899) were the most frequent on the flowers and are the most likely potential pollinators, as suggested by their contact with floral reproductive structures and adhesion of pollen to their bodies.