Floral development of Triaenophora (Veronicaceae) and phylogenetic implications

Abstract

The floral development of Triaenophora has been studied in order to explore the developmental basis for the phylogenetic relationship between Triaenophora and allies in Veronicaceae. The simple raceme with a subtending bract and two lateral bracteoles for each flower is probably derived from a compound inflorescence consisting of basic units of 3-5-flowered cymes. The initiation sequence of the calyx and corolla lobes fits into the common pattern of Digitaleae and Veroniceae. The delay in early growth of the corolla and aestivation is intermediate between Digitaleae and Veroniceae. Only four stamens are initiated, with a gap at the expected site of the fifth stamen. The occasional re-occurrence of the fifth stamen as a staminode is probably a reflection of an ancestral feature as in Digitalis. The affinities of Triaenophora within Veronicaceae are discussed based on comparative floral development.