Floral ontogeny of Salpiglossis (Solanaceae) and the oblique gynoecium

Abstract

Inflorescence development in Salpiglossis consists of repeated modular units consisting of two floral bracts on an axis terminating in a flower. The calyx is initiated in a helix with the first primordium appearing on the abaxial side of the floral apex. Primordia of the corolla, androecium, and gynoecium arise in three successive whorls. Zygomorphy first becomes manifest with the slightly delayed initiation of a staminodial primordium. Growth of the corolla and androecium show a dorso-ventral asymmetry that also results in zygomorphy. During early development the median plane of many flowers is on the axillary plane. The median plane of other flowers is oriented 10-15° off the axillary plane, but this is less than half the expected 36°. The off-median orientation does not produce the oblique gynoecial orientation described in the literature as a defining feature of Solanaceae. The zygomorphic flowers of Salpiglossis have a gynoecium that is on the median plane and not oblique. Further the flowers are not obliquely oriented unless via pedicel rotation prior to anthesis. The floral orientation of Solanaceae, as exemplified by Salpiglossis, has the staminode and a calyx lobe in the abaxial position, which is a synapomorphy with respect to other Asteridae.