Christian Westerkamp

Keel blossoms: bee flowers with adaptations against bees

Summary Flowers from diverse angiosperm families conceal their pollen within a keel. Visitors in search of nectar enter the narrow entrance between the movable keel and the opposed immovable flag. Thus, they secondarily release (doses of) pollen from its cover. As bees are the only visitors able to handle these flowers and thus their essential pollinators on one hand and the only pollen foragers on the other hand, keel blossoms are best understood as an adaptive response of plants to the dilemma of strong competition for pollen between flowers and bees.

From keel to inverted keel flowers: functional morphology of “upside down” papilionoid flowers and the behavior of their bee visitors

Most Papilionoideae species exhibit specialized flowers with the standard petal placed in the upper position and the keel and surrounding wings acting as the landing platform for bee visitors. For some groups, however, flowers became resupinate so that bees land at the standard petal. In this upside-down morphology, the pollen is deposited onto the dorsal side of visitors, instead of the ventral side as in most keel flowers. To understand how these inverted keel flowers work and their differences from normal keel flowers, we studied the resupinate species Canavalia brasiliensis, Centrosema pascuorum and Clitoria fairchildiana, and compared with the normal keel Lathyrus pubescens, Crotalariamicans and Dioclea violacea. Both the behavior and morphology of bee visitors were observed and compared to the flower morphology. We observed that most features of the mechanism exhibited by inverted keel flower are found at keel flowers, except for three key innovations: a thickening at wings’ margin in contact with the visitors’ body, tighter interlocking between petals and strengthening of the vexillum structure. Most visitors are adapted to flower characteristics in their morphology and behavior, although some act as thieves due to some of their morphological features, such as mouthpart length. In spite of their differences, bees behave almost in the same way when visiting both normal and inverted keel morphologies. Compared to keel flowers, inverted keel flowers evolved toward more restrictive structures that require large-bodied bees to operate them. Finally, we discuss possible selective pressures that might have led to the evolution of inverted keel flowers.

A arborização alienígena de Fortaleza (nordeste do Brasil): observações qualitativas e um levantamento em dois bairros

Public tree planting is important for cities. It produces shadow, brings well-being for humans, and supports the urban fauna. But the cultivation of alien plants can also be responsible for the dissemination of exotic species. This paper aims to evaluate public tree planting in Fortaleza, Ceara state, in northeastern Brazil. From 2005 to 2009, qualitative observations on tree compositions were made. In 2006, a detailed inventory of all trees was carried out in two districts of Fortaleza. Jointly, 2075 individuals grew here. Most of the tree species planted in Fortaleza are aliens, some are even invasive. The massive use of exotic plants in Fortaleza has negative consequences for the environmental education. People do not know the regional native trees, and thus are not concerned about the local biodiversity conservation. In spite of the huge amounts of native species available for ornamental purposes in the Brazilian flora, the street trees of Fortaleza are overwhelmingly aliens.

Naturalization and potential impact of the exotic tree Azadirachta indica A.Juss. in Northeastern Brazil

Invasive species are among the leading causes of biodiversity loss on the planet, and some species that have become invasive were intentionally introduced for ornamental or commercial purposes. Azadirachta indica A.Juss. (Indian neem) is an exotic species that is widely cultivated in the northeastern region of Brazil, both in plantations and as an ornamental or shade tree, where it has reached reproductive phase in recent years. In order to assess its level of naturalization and the geographic range where this species has reproductive capacity, we observed A. indica specimens cultivated in Fortaleza (Ceara) since 2006 and performed field observations in several other localities in Ceara, Rio Grande do Norte, Paraiba and Piaui states. Currently, the species reproduces near the coast as well as in the semiarid interior of the Northeast, and is able to establish regenerating populations. Thus, the species is naturalized in Brazil with the potential to become invasive in the near future.