The Ligule in Poaceae: a Historical and Evolutionary Review

Ligules are classified, predominantly, on their position and morphology, which are still without a consensus as to their nature and diversity in an evolutionary context in Poaceae. Based on a broad review of this structure, we have identified five hypotheses for the definition of ligules, originating between the years 1800 and 1834; some of these hypotheses are still valid today. Our results also demonstrate that 95.28% of the family representatives have homoligulate ventral ligules and 1.75% have heteroligulate ventral ligules, with Panicoideae being the subfamily with the greatest morphological diversity of ligules. Dorsal and culm leaf ligules occur mainly in Puelioideae and Bambusoideae (except in Olyreae), and may occasionally occur in Pooideae, Panicoideae and Chloridoideae. Although homoligulate and ciliate ventral ligules are ancestral states in the Poaceae, several reversals occurred within the subfamilies so that the eciliate membrane type is more common (especially in the BOP clade).

Automated summary

The classification and diversity of ligules in Poaceae plants are still a subject of debate, with different hypotheses proposed. This study found that the majority of Poaceae representatives have homoligulate ventral ligules, with Panicoideae subfamily displaying the greatest morphological diversity. Dorsal and culm leaf ligules mainly occur in Puelioideae and Bambusoideae, and reversals in ligule types have occurred within subfamilies.