Taxonomic circumscription of the N African endemic Biscutella raphanifolia (Brassicaceae) based on morphological and molecular characters

Abstract

Biscutella raphanifolia is a species distributed in N Algeria and Tunisia, characterized by the presence of large, lyrate basal leaves, amplexicaul cauline leaves, and paniculate-branched inflorescences. It has been traditionally considered the only perennial taxon from B. sect. Biscutella, lifespan being the strongest argument used to differentiate B. raphanifolia from other annual taxa such as B. algeriensis, B. confusa or B. didyma var. coriophora, with which it shares both morphological characters and distribution. Reevaluation of morphological characters in the light of phylogenetic trees from plastid (rpl32-trnL and trnV) and nuclear (ITS region) sequence data support a new circumscription of B. raphanifolia to include all those annual taxa. As a result, the new combination B. raphanifolia var. algeriensis is established, descriptions are provided for both varieties, and synonyms and lectotypes are indicated or designated for the names concerned.