Floral Development of Agalinis neoscotica, Agalinis paupercula var. Borealis, and Agalinis purpurea (Scrophulariaceae): Implications for Taxonomy and Mating System

Abstract

Floral development from initiation of primordia through anthesis was studied for three closely related species of Agalinis. Objectives were to determine the developmental basis for the mixed mating system in Agalinis neoscotica, to compare its ontogeny with that of Agalinis paupercula var. borealis, which may also have a mixed mating system, and with that of Agalilnis purpurea. The latter taxon has large, showy, herkogamous flowers and probably has a mating system dominated by outcrossing. Several developmental events differ among the taxa, and some of these are related to differences in mating system. Closure of the calyx of A. paupercula var. borealis is delayed relative to other Agalinis. Taxa differ in relative time of appearance of petal and stamen primordia and production of cilia and trichomes on corollas. A number of developmental features characterize A. neoscotica, a small-flowered taxon known to self-pollinate. Onset of meiosis and ovule initiation are precocious. Few or no trichomes develop along the stomia of precociously opening anthers in A. neoscotica, unlike other Agalinis, allowing pollen to fall on the stigma. The style is straight, and the short stigma is positioned among the anthers before anthesis. The stigma splits into two lobes with stigmatic papillae on the exposed surfaces in A. neoscotica, a feature unknown in other Agalinis and related genera. Anthers dehisce in bud. In other Agalinis the style elongates and bends over the anthers so the stigma is held behind the anthers next to the corolla wall before anthesis. The sharply bent style straightens and elongates as the corolla opens; thus the stigma is kept above and in front of the dehiscent anthers in herkogamous species such as A. purpurea. The evolution of self-pollination and mixed mating in A. neoscotica from a herkogamous ancestor would have necessitated addition and deletion of characters and heterochronic changes during ontogeny. Differences in the ontogenies of the three taxa support the view that the taxa are separate species.