Nectar spurs are tubular outgrowths of a floral organ that contain or give the appearance of containing nectar. They are hypothesized to be a ‘key innovation’ leading to rapid speciation within a lineage because they are involved in pollinator specificity. Cullen et al. utilise the natural variation in spur length present in a clade of Iberian toadflaxes, Linaria (Plantaginaceae), to probe the developmental basis of variation in nectar spur length.
They found that changes in cell number and therefore in cell division largely explain evolution of spur length in Linaria. This contrasts with previous studies in Aquilegia (Ranunculaceae) that have found variation in nectar spur length to be due to directed cell expansion (anisotropy) over variable timeframes. This study adds to knowledge about nectar spur development in a comparative context and indicates that different taxa may have evolved nectar spurs using disparate mechanisms.