Leaflet secretory structures of five taxa of the genus Zornia J.F. Gmel. (Leguminosae, Papilionoideae, Dalbergieae) and their systematic significance.

Abstract

A survey of the secretory structures of leaflets has been carried out for five taxa of the genus Zornia J.F. Gmel. to assess possible taxonomic value of the glands, taking into account that these taxa, Zornia curvata Mohlenbr., Z. gemella Willd. ex Vogel, Z. glabra Desv., Z. latifolia Sm. and Z. reticulata Sm., have overlapping diagnostic characters. The leaflet secretory structures of the five studied taxa of Zornia were mucilage epidermis, mucilage cavities, and idioblasts secreting phenolic compounds. Mucilage epidermis is found in all five aforementioned taxa. Mucilage cavities are observed on both epidermal surfaces of the leaflets in four taxa, the exception being Z. glabra, whose cavities occur only on the abaxial surface. Idioblasts secreting phenolic compounds were detected only in the mesophyll of Z. latifolia and Z. reticulata. The joint occurrence of mucilage epidermis with mucilage cavities seems to be of unifying value for the five taxa analyzed. The position of mucilage cavities and the occurrence of secretory idioblasts in the mesophyll of the leaflets are of diagnostic value, providing a key to enable identification of the taxa studied. This study reveals that the secretory structures provide important information in support of systematic studies of the Leguminosae. In relation to the five taxa of Zornia studied, current results suggest recognition of four species: Z. curvata, Z. glabra, Z. latifolia, and Z. reticulata.