Keel flower
A pea-family flower whose lower petals form a keel that must be forced open — filtering visitors by strength rather than tongue length.
Definition
Clovers, vetches, gorse, broom and alfalfa all use this architecture. A bee has to push the keel down to reach the reward, which favours heavier bees. Broom's keel splits explosively and whips the style over the insect's back; alfalfa's trips and strikes the bee on the head, which honey bees find aversive enough to learn to rob the flower from the side instead.
Where the word gets used loosely
The alfalfa case is the clearest demonstration that visiting is not pollinating. A honey bee robbing alfalfa from the side collects nectar and pollinates nothing, which is why the seed industry runs on leafcutter and alkali bees that tolerate being tripped.
Plant records that discuss this
- AlfalfaExcellent forage on paper, and the tripping mechanism complicates it in practice: a honey bee robbing nectar from the side of the flower collects no pollen and delivers none.
- Bird's-foot trefoilGood for both, over a long season, from a plant that thrives on the poor unimproved ground most other forage will not tolerate.
- GorseZero nectar and top-rated pollen, available in midwinter. Alongside hazel and poppy it is the clearest argument for rating the two separately.
- Tufted vetchVery high for both, and specifically valuable to the long-tongued bumblebees that have declined most sharply.
- KaranjA good nectar and pollen source at the thinnest point of the Indian year.
See also
Other botany terms
Sources
Sources
- Field Guide to the Bees of Great Britain and Ireland — Bloomsbury (2015) · Field guide
- The Bees of the World — Johns Hopkins University Press (2007) · Textbook
How sources are selected and weighted is set out in the sources and evidence policy.