Confirmation of distyly in Perovskia and floral dimorphism of P. abrotanoides (Salviinae: Lamiaceae)

Abstract

Heterostyly is a specialised reproductive system with a reciprocal arrangement between the stamen and style, and often associated with tubular actinomorphic flowers. Accordingly, heterostyly is extremely rare in Lamiaceae, a representative zygomorphic flower group. However, some evidence indicates the occurrence of heterostyly in Perovskia. To confirm the existence of heterostyly, 288 herbarium specimens of Perovskia were observed, and a detailed floral morphological study was conducted on P. abrotanoides as a representative to diagnose the evolution of heterostyly. All examined specimens could be divided into two groups: a long-styled morph (L-morph) and a short-styled morph (S-morph), while P. abrotanoides, P. angustifolia, P. atriplicifolia, P. botschantzevii, and P. scrophulariifolia were recognized as distylous taxa. In P. abrotanoides, L-morph flowers possessed a larger calyx, a longer corolla, stigma, and anther, while significantly larger pollen grains and wider corolla were detected in S-morphs. Micromorphological structure and distribution patterns of trichomes were identical to both floral morphs, but the stomatal size on leaves and density of specific trichomes were somewhat different between morphs. Collectively, all data indicate a stable distylous condition of P. abrotanoides as the first case showing general heterostylous syndrome within Lamiaceae.