Patterns of nectar production and composition, and morphology of floral nectaries in <i>Helicteres guazumifolia</i> and <i>Helicteres baruensis</i> (Sterculiaceae): two sympatric species from the Costa Rican tropical dry forest

Abstract

Helicteres guazumifolia Kunth and Helicteres baruensis Jacq. (Sterculiaceae) are two sympatric species of shrubs common along the North Western tropical dry forest of Costa Rica. I recorded their nectar production within a 24 hour cycle. I also describe the morphology of extrafloral nectaries with scanning electron microscopy. In H. guazumifolia secretion was restricted to the first day of flower life span, shortly after anthesis (0600 hr - 1800 hr). Flowers secreted on average 15.63 ±8.45 μl (N=409). Nectar is composed of three main sugars: sucrose, fructose and glucose (mainly sucrose). A total of 17 free amino acids were identified: mainly proline, arginine, threonine and tyrosine, with a concentration above 70 Ng/μl. Values were different for H. baruensis. Nectar secretion was confined to the second day after anthesis, starting at 1600 hr and ending at 0600 hr the following day. Flowers secreted on average 77.03 ±64.99 μl (N=163) of nectar. Nectar is also composed of three main sugars; however, it showed a tendency to be hexose-rich, having more fructose and glucose than sucrose. There were also 17 free amino acids, mainly proline, alanine, tyrosine, arginine and threonine. Patterns of nectar production are different between the two species for timing, and for amount and composition of nectar secretion.