Using leaf anatomy to solve taxonomic problems within the Anemopaegma arvense species complex (Bignonieae, Bignoniaceae)

Anemopaegma is a monophyletic lineage included in the tribe Bignonieae. The genus is taxonomically problematic, especially in the Anemopaegma arvense species complex, a group whose taxa have been delimited on the basis of leaf external morphology. Here we study the leaf anatomy of all three species and nine varieties currently included in this species complex (A. acutifolium DC., A. arvense (Vell.) Stellf. ex de Souza and A. glaucum Mart. ex DC.) in search for additional characters that may help circumscribe taxa within this group. For comparison, this study also investigated the leaf anatomy of two species that are morphologically similar to representatives of the species complex but currently placed outside it (A. album Mart. ex DC. and A. scabriusculum Mart. ex DC.). All taxa were analyzed using standard anatomical procedures and light microscopy. In addition, leaves of A. acutifolium and Anemopaegma album were analyzed with scanning electron microscopy (SEM). Overall, stomata position, composition of the vascular system of the petiole, midrib, lateral veins and margin constitution represented the most important anatomical features for the recognition of the species and varieties. The study also demonstrated that A. scabriusculum presents leaf anatomical traits that differ from those encountered in species of the Anemopaegma arvense complex, corroborating earlier anatomical and molecular phylogenetic results and indicating that A. scabriusculum is indeed best placed outside the A. arvense species complex. Leaf anatomical data also support the synonymization of some varieties of A. mirandum with A. arvense, as well as varieties of A. glaucum into this species.