Atypical pseudopollen‐forming hairs in Maxillaria (Orchidaceae)

Pseudopollen is found on the labella of several species of Maxillaria and is formed by the fragmentation of uniseriate, multicellular, moniliform trichomes. The resultant component cells are rich in protein. Since flowers of pseudopollen‐forming species generally lack nectar, it is probable that pseudopollen gradually replaced nectar as the pollinator reward. However, direct evidence for this hypothesis is lacking. The present paper examines the labellar micromorphology of five Brazilian species of Maxillaria assigned to the M. discolor alliance. The flowers of two of these species, namely M. violaceopunctata and M. villosa , produce both food hairs and a lipoidal, labellar secretion which is rich in aromatic amino acids. Moreover, in the case of M. violaceopunctata , the secretion was found to contain reducing sugars. This may represent an intermediate stage in the transition from nectar‐producing to pseudopollen‐forming flowers. SEM studies indicate how pseudopollen‐forming, moniliform trichomes, such as those found in the Maxillaria grandiflora complex, may have evolved from simple, uniseriate, multicellular hairs. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143 , 151−158.