Asteraceae inflorescence meristems are physically constrained as to the position of the individual floral meristems so that the floral primordia are tightly packed. New floral meristems are generally initiated in regular phyllotactic spirals at an angle of 137.5 degrees that converge at the apex of the inflorescence as shown by several recent studies that have plotted and quantified the positioning of floral primordia on simpler Asteraceae models. The models are not absolute for all taxa in the Asteraceae, however. Certain basal taxa in the tribe Heliantheae display a marked deviation from the expected pattern of packing. Most of the taxa of the subtribe Engelmanniinae (sensu Clevinger and Panero), including Engelmannia, Berlandiera, Chrysogonum, and Lindheimera produce peripheral multi-meristem complexes that consist of one ray flower primoridium, two or more disk flower primordia as well as the associated involucral and receptacular bract primordia. These primordia complexes act as coordinated units as far as timing of initiation and development is concerned and also display distinct heterochronic development when compared to their closest neighbor floral and bract primordia. They remain evident at anthesis and beyond as cypsela complexes that presumably aid in dispersal. Some (but not all) species of the terminal taxon of the Engelmanniinae, Silphium, possess similar primordia complexes but do not go on to develop cypsela complexes. The trait is completely lacking in some of the more basal members of the subtribe: Dugesia, Wyethia, and Borrichia.

Key words: cypsela complex, Engelmanniinae, inflorescence bauplan, phyllotactic spirals, primordia complexes