The Bromeliaceae were surveyed for petal appendage morphology using light and scanning electron microscopy. Three general morphological types were recognized, each loosely correlating with one of the three subfamilies. Petal appendage elaboration and variation were greatest in the Bromelioideae, while subfamilies Pitcairnioideae and Tillandsioideae exhibit more simplified, consistent morphologies. All Pitcairnioideae examined with petal appendages possessed a single appendage per petal, as opposed to two appendages per petal for the Bromelioideae and Tillandsioideae. Analyses of floral ontogenetic sequences revealed that, in all cases, petal appendage initiation is a late developmental event with petal appendages being the last formed external multicellular structures. There has been an overemphasis in the use of the presence of petal appendages in the circumscription of generic limits in the Bromeliaceae. and especially in the Tillandsioideae (e.g., Tillandsia vs. Vriesea).
American Journal of Botany
Brown, Gregory K. and Terry, R. G. (1992). "Petal Appendages in Bromeliaceae." American Journal of Botany 79.9, 1051-1071.