Diversity and evolution of the ligule and contraligule in Scleria and related genera (Cyperaceae)

Abstract The monocot leaf is typically composed of a sheath and a blade, but many other structures may be present, interpreted as modifications of the sheath or the lamina, or as sui generis structures, such as ligules and contraligules. We investigate both structures in Scleria (Cyperaceae) through a literature review, morphology, anatomy, and ancestral state estimation, discussing their concepts and diversity. The concept of ‘contraligule’ is not uniform in the literature, with at least three conflicting definitions. The morphological diversity of the contraligule represents a continuum of development, and the distribution of trichomes on the ligule and the contraligule presents a considerable diversity. Anatomically, the ligule exhibits a pattern similar to what is found in some groups of Poaceae. The ancestor of Scleria probably had a deltoid contraligule that diversified within the genus. Both the ligule and the membranous appendix on the contraligule arose independently more than once in Scleria. To standardize the terminology within the family, we suggest that the definition used for Scleria be expanded to include Cyperaceae.