Can a Texas bluebonnet change its spots?

Texas bluebonnets (Lupinus texensis) are prolific in the early spring and are known for attracting an array of native bees as well as honey bees. This species is one of the five state flowers of Texas, the other four being also in the genus Lupinus. (We’ve all heard strange things about Texans, so we’ll just ignore this for now.)

The interesting thing about Texas bluebonnets is the bright white spot on the banner (upright portion) of each floret. Bees are extremely attracted to these bright spots and can collect a large quantity of high-quality pollen from the florets. As the florets age, however, the white spots turn a purplish-red and the bees are much less attracted to them as a result. At the same time that the spot changes color, the pollen becomes less abundant, less fertile, and less sticky.

This confluence of events just happens to be good for the bees and good for the plant. It is good for the bees because they can efficiently collect lots of nutritious pollen without having to expend energy checking the purple-spotted florets. In addition, the pollen is so sticky the bees can carry large loads of it back to their hives or nests.

It is good for the plant because it means that the bluebonnets–which are dependent on insect pollinators–are pollinated with fresh, fertile pollen rather than with older, drier, and less fertile pollen. This, in turn, assures that a large crop of high quality seeds will be produced from the flowers. It is definitely a win-win situation–what we call a plant-pollinator mutualism.

In a paper published in The Southwestern Naturalist [1], Schaal and Leverich found that bees can collect up to 150 times more pollen from a white spotted floret than a purple-spotted one. Other research has revealed that nearly all pollinator visits (about 96%) were to the florets with white spots.

Now that you’ve absorbed this cool little tidbit of pollination ecology, you can go back to wondering why on earth Texas has five state flowers. Hmm.

Rusty

[1] Schaal, Barbara A. and Wesley J. Leverich. 1980. Pollination and Banner Markings in Lupinus texensis (Leguminosae). The Southwestern Naturalist 25(2): 280-282.

Texas bluebonnet. Older florets at bottom have already turned dark. Flickr photo by alamosbasement.
Texas bluebonnet. Older florets at bottom have already turned dark. Flickr photo by alamosbasement.

Comments

PerriAngela Wickham
Reply

Didn’t know this about bees and bluebonnets! Very interesting. Thanks for posting. I think I’ll try to find the original paper to read. : )

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