Why do botanists disagree about how to classify some Cyperaceae genera such as Scirpus?

Botanists disagree on the classification of certain Cyperaceae genera, such as Scirpus, primarily because of the difficulty in defining their limits and circumscription.1

In the case of Scirpus, historical broad definitions have included up to 300 species, resulting in a group that is extremely diverse and contains several fundamentally different morphological forms and embryo types. To better reflect evolutionary relationships, many botanists now recognize Scirpus in a narrow sense, limiting it to the leafy bulrushes (approximately 40 species) and separating other species into distinct genera such as Bolboschoenus, Isolepis, Schoenoplectus, and Trichophorum.1

These taxonomic challenges arise because the family’s nonreproductive parts are rather uniform, and the flowers are highly reduced, making it difficult to deduce evolutionary patterns from living plants. Consequently, classification often relies on the morphology of spikelets, and different interpretations of these structures—or the evolutionary significance of unisexual versus bisexual flowers—lead to ongoing debate among authorities.21