Erythrina Oliviae: A New Case of Oriole Pollination in Mexico

Abstract

Erythrina oliviae, a dry-season-flowering tree from Mexico, is primarily pollinated by perching passerine birds. Other pollinators have also been noted. The nontubular flowers are directed to the ground, and the keel and wings function as nectar containers. The perch is vertical. The flowers produce large amounts of nectar, which contains a low percentage of sugar and a high number of amino acids. It is possible to recognize two basic patterns in the flower structure of genus Erythrina (Leguminosae): (1) the standard enormously elongated and the keel and wings reduced to minimal size, and (2) the standard ovate or obovate and the keel and wings more or less conspicuously exserted from the calyx. In the first case the flower takes a decidedly tubular shape, and in the second it assumes a more generalized gaping configuration. A general correlation between these flower structures and pollination types may be also assumed. In the first case, the flowers can apparently be visited and pollinated efficiently only by hummingbirds,3 and all the species, except the small African sect. Humeanae Barneby & Krukoff, with this kind of flower are from the New World (Raven, 1974, 1977; Toledo, 1974). In the second case the flowers are generally adapted to perching-bird pollination (Docters van Leeuwen, 1932; Singh, 1929; Ali, 1932), although they are also visited by hummingbirds, insects, squirrels and bats (Raven, 1977) and are predominantly, but not exclusively, from the Old World. In fact, a review of Krukoff & Barneby's (1974) conspectus of Erythrina shows that although the majority of American species (55) have tubular flowers and are therefore hummingbird pollinated, there are also a few species (12) with more generalized flowers (Table 1). The studies of pollination biology in this second group of species are very relevant because in it are included the species of subgen. Micropteryx, which has been considered the most primitive of the genus, and therefore perching-bird pollination in America may be considered an archaic syndrome which apparently preceded pollination by hummingbirds. At present, the data that have appeared about the pollination of American species of Erythrina with nontubular flowers seem to indicate that in this group both passerine bird pollination and hummingbird pollination is possible. They suggest 'We are grateful to M. Sousa for providing information about the species studied. We wish to thank M. Campomanes for amino acids analysis of nectar, L. Herrera who made the illustrations, and Alfonso Delgado for reading the manuscript. Finally we are especially grateful to Dr. Peter H. Raven for encouragement and for providing information, and Dr. Rupert Barneby for critically reading the manuscript. 2 Instituto de Biologia, Universidad Nacional Autonoma de Mexico, Apdo. 70-233, Mexico 20, D. F., Mexico. 3The following may be an exception; although van der Pijl (1937) proposed a possible disharmony between Asiatic flower-birds and American bird-flowers, Doctors van Leeuwen (1932; 93) refers to the case of the Venezuelan Erythrina (E. umbrosa H.B.K. which is a synonym of E. mitis Jacquin) which is cultivated in Java and visited by three species of sunbirds. ANN. MIssouRi BOT. GARD. 66: 503-511. 1979. 0026-6493/79/0503-0511/$1.05/0 This content downloaded from 207.46.13.122 on Thu, 19 May 2016 04:53:17 UTC All use subject to http://about.jstor.org/terms 504 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 66 TABLE 1. American species of Erythrina with nontubular flowers.