Nectar spur

Nectar spurs have been cited as prime examples of “key innovations” that may promote diversification, and play a part in the adaptive radiation of clades.

[3] However, there has also been some refutation to this idea recently, suggesting that the adaptive radiation of Aquilegia may have been due more to climate and habit than to the varying lengths of the nectar spurs.

[12] Studies in model plant Antirrhinum and Arabidopsis identified that type I KNOX SHOOTMERISTEMLESS (STM) genes play a role in the development of spur-like structures.

[13] These type I KNOX STM genes also play important roles in the development of the growing tip of the plant, the shoot apical meristem, by controlling cell division and prolonging indeterminate growth.

[15] However, the type I KNOX homologues were not differentially expressed during spur development on the petals of Aquilegia, while certain TCP genes instead were suggested to play a role.

Nectar spurs on Aquilegia.
Side view of Tropaeolum majus , a plant with a nectar spur arising from the hypanthium of the flower.
The long tongue of a sphinx moth is depicted as reaching into the equally long-spurred orchid.