Floral Structure of Besseya and Synthyris (Scrophulariaceae)

Abstract

The floral structure of Besseya and Synthyris was examined to clarify corolla variation and delineate characters for phylogenetic analysis. Inflorescences of both genera are racemes, although those of Besseya have more numerous flowers that are more compactly arranged than in Synthyris. Inflorescence changes may be associated with perianth variability, including the diminution of the corolla in B. rubra and its loss in B. wyomingensis. Besseya was originally segregated from Synthyris because its corolla is bilabiate and lacks a basal tube. The corolla bilabiation and lack of a tube in Besseya arise as part of the same evolutionary modification-a cessation or diminution of zonal growth in the corolla in the region of stamen insertion. The androecium of Besseya and Synthyris consists of two stamens, conforming to the prevalent pattern of tribe Veroniceae. Like most other Scrophulariaceae the synovarious, bicarpellate gynoecium has a paracarpous region in the upper portion of the ovary. The carpellary septa in this region appear postgenitally united.