Diversity and functional roles of floral glands in Malpighiaceae: insights in Lophopterys floribunda W.R. Anderson & C. Davis.

Abstract

Lophopterys floribunda is a Neotropical species of Malpighiaceae endemic to Brazil, occurring in both the Amazon and Atlantic Forest. Instead of the typical bi-glandular sepals reported for Neotropical Malpighiaceae, this species presents a single, large gland on the lateral sepals. In addition, ant patrolling was observed at the apex of bracts and bracteoles during fieldwork. Thus, this work aimed to describe the sepalar gland of L. floribunda and other secretory structures in its flowers and inflorescence. Samples of bracts, bracteoles, sepals, petals, and anther were collected and submitted to usual anatomical techniques. Unexpected nectaries at the apex of bracts and bracteoles, not visible to the naked eye, were described and represent a new type of structure for the family due to both their position and size. Mutualistic ants consume the exudate produced by these tiny nectaries, and such structures enable a specific visitation pattern for Lophopterys. Typical epithelial elaiophores occur on the lateral sepals, formed by an invaginated epidermis, which predominantly produce lipid secretion. The petal marginal glands are anatomically similar to the standard type of colleter, which exude mucilaginous substances. The exudate produced by the petal marginal glands was considered to have an additional role of contributing to the maintenance of the closed bud during the beginning of development. The globose epidermal cells containing lipids, proteins, and polysaccharides observed in the connective may be responsible for the typical aroma emitted by these flowers. The diversity of secretory structures reported here has application in both systematic and ecological studies of Malpighiaceae.