Bee Pollination

Biol 324 Introduction To Seed Plant Taxonomy

Characteristics of bee pollinated flowers

Traits
- Bee flowers typically yellow or blue, with nectar guides or UV patterns, usually fragrant, often zygomorphic, sometimes with a broad tube, or a narrow tube when pollinated by long tongued bees (sometimes without nectar but producing pollen as a reward)
- Bees are common and efficient pollinators: cannot see red but can see ultraviolet, and can distinguish bilaterally symmetrical patterns
- Bees feed on nectar and pollen, but some tropical bees collect scent compounds for mating behavior or resins for nest building from specially adapted flowers.

UV floral patterns
Bees have good vision in the ultraviolet part of the spectrum, which we cannot see. Consequently many bee-pollinated flowers have striking UV patterns. E.g. Potentilla anserina (Rosaceae). We see yellow flowers, but bees see margin of light with a centre of dark…a "bull’s eye" pattern.

Bee pollination example:
Pollination of Cytisus scoparius (Scotch Broom – an invasive plant in BC). Almost all legumes are bee pollinated (a few have transitioned to bird pollination)

Mechanism of pollination in Cytisus
- stamens and style are held under tension by the keel (lower two petals shaped like the
keel of a boat), because the upper edges of the two keel petals are connate.
- When a bee lands on the keel and depresses it, the keel petals open releasing the the stamens and style, which spring upward showering the bee with pollen. The stigma also hits the bee (bees must be appropriate size)

Rewards
Cytisus has 5 short stamens which hit the bee ventrally - 5 long ones which curl around and hit the
bee dorsally. The stigma also hits the bee dorsally. The bee uses the ventral pollen for food; dorsal pollen is in a "safe zone" and cannot be easily groomed by the bee, so mainly serves for pollination. (Pollen is the reward in this system.) After the "tripping" of the flower by bees, the keel and wings hang limp, the stamens and style are exposed, and other bees do not visit the flower.

See also:
Pollination of //Aconitum//

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