Plicate Staminal Filaments in Tillandsia Subgenus Anoplophytum (Bromeliaceae)

Plication of stamina!filaments is an important diagnostic character for Tillandsia subgenus Anoplophytum (ca. 45 species). The monophyletic integrity of subgenus Anoplophytum has recently been questioned, and we conducted an anatomical investigation of plicate stamina! filaments to better characterize this putative synapomorphy. Developmental studies show that the filament plications, or folds, become visible during or soon after anthesis. Serial sections of preplication filaments and filaments in sequential stages of plication were prepared and observed with light microscopy. A uniform sequence of parenchyma cell collapse begins three to four cell layers out from the vascular bundle and proceeds centrifugally to the epidermis. Eventually the epidermal cells collapse, leaving only the vascular bundle and a few surrounding parenchyma cells intact. Above and below the zone of plication, all parenchyma and epidermal cells in the filament remain intact. Species traditionally placed in subgenera Tillandsia and Allardtia have been found with plicate stamina! filaments that are anatomically and develop­ mentally identical to those studied from subgenus Anoplophytum. Alone, stamina! filament plication does not appear to be a good diagnostic character for subgenus Anoplophytum, and doubts concerning the monophylesis of this subgenus are reinforced. The functional significance of stamen filament plication remains unknown