A taxonomic revision of Calendula (Asteraceae) in Morocco, including some taxa from Algeria and Tunisia

Abstract

On the scope of a full taxonomic revision of the genus Calendula (Asteraceae), the morphological patterns in taxa of Calendula occurring in Morocco and some additional taxa from Algeria and Tunisia were analyzed. This genus was inadequately studied in the SW Mediterranean region, in particular the perennial plants with 2n = 32 (commonly included in C. suffruticosa and C. incana) as specimens of these plants held in herbaria generally lacked achenes, which are essential for proper classification/identification. The classification, relationships, distribution and evolution of these Calendula taxa were assessed using principal components analysis, further supported by chromosome numbers and genome size estimations. Morphometric analyses among and between the C. maroccana and C. suffruticosa groups revealed that the major delimiting characters belong to the morphology of the achenes. A taxonomic treatment for Calendula in the SW Mediterranean region (Morocco, Algeria and Tunisia) is, therefore, presented, based on observations in the field and study of herbarium specimens. Two new species (C. davisii and C. oualidii) and eight new subspecies of C. suffruticosa are described. Six lectotypes and one neotype are designated. Identification keys, taxon descriptions, synonymy, type citations, conservation assessments and notes on distribution and habitat, are also provided. There are 12 species of Calendula in Morocco, of which 8 are endemic. Four species are assessed as Critically Endangered and three as Endangered.