Abstract
Lupinus L. comprises approximately 280 species, with high diversity in the Americas. Nearly 65 species are reported in Mexico, of which 50% are endemic. While several efforts have been made to investigate this diversity using morphological and phytochemical descriptions of the vegetative and reproductive organs in some of their species, little is known about the foliar anatomy of Mexican lupins. Therefore, to gain a more detailed understanding of the structural diversity of the genus, an anatomical description of the leaves of three Mexican species (L. bilineatus Bent., L. hintonii C.P. Smith, and L. mexicanus Cerv. ex Lag.) was carried out. For this purpose, leaflets and petioles of the three species were collected from various locations along the Trans-Mexican Volcanic Belt; they were fixed for 24 hours and processed using conventional histological techniques for embedding with paraplast. Permanent preparations of cross-sections stained with safranin fast green were obtained from both leaflets and petioles, as well as temporary preparations of the leaflet epidermis. The anatomy of the dermal, fundamental and vascular tissues of the leaflets and petioles of the three species is described, characterizing structures of the adaxial and abaxial ends such as: the cuticle, trichomes, papillae and cells as part of the dermal tissue, as well as the mesophyll and its intercellular spaces of the fundamental tissue and finally the vascular bundle of the middle vein of the leaflet and the petiole. Despite the consistency of certain foliar characteristics in Lupinus species, such as the presence of a single-layered epidermis and epidermal papillae on the leaflet and petiole, most of the traits described here were highly diverse among species. These included cuticle thickness, trichome density, and the number of surrounding basal cells, the stomatal index of both organs, the presence of intercellular spaces in the storage parenchyma, and the size of the midrib in the leaflet. It is discussed the variable characteristics and their relationship to environmental conditions. These results allow for a greater understanding of the foliar anatomy of Mexican Lupinus species, as well as providing further support for the structural diversity that can occur in this genus.