Friday, September 11, 2009

Bitterweed in Bloom

Throughout the year there has been a yellow flower in bloom along roadsides and undisturbed field margins. To the casual observer they may seem to be the same flower. However, there has been a progression from dandelion to buttercups to groundsel to mustards to coreopsis. Each has occupied the same ground, replacing its predecessor without a trace. The next bright yellow flower to come into bloom is bitterweed. Bitterweed belongs to the important bee plant family, the composites, or sunflower family, as do each of its predecessors except the mustards. The composite flowers provide both nectar and pollen for the honey bee.

Click on the photo and you can see that this honey bee is foraging for pollen from the bitterweed. You can see the orange-colored packets of pollen in the bee’s pollen baskets on her hind legs. The same honey bee will not forage for both nectar and pollen. Other honey bees from the hive will visit this bitterweed plant for nectar. As Charles Darwin observed, the honey bees foraging on bitterweed will continue to forage bitterweed as long as it continues to be useful. This behavior is called flower constancy. Foragers are visually guided to the plant by its bright color and the shape of the petals as well as the interruptions between petals. A honey bee has no trouble telling a bitterweed from a golden aster blooming nearby. Ultraviolet nectar guides direct the honey bee to the nectary in the center of the flower. Bitterweed growing in pastures is normally passed over by grazing cattle. If dairy cattle feed on bitterweed, it is said that it will make the milk bitter. As honey bees forage on bitterweed and other fall flowers, the flavor of the honey changes from the mild flavored honey of the summer to a much more robust honey.

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