Crotalaria spectabilis (not native) CLICK
What wild-growing flower is the most eye-grabbing? Showy Rattlebox is on the good-looking list. It is as big and colorful like a garden flower, and I always assumed that it’s a garden escape, but a little Google research indicates this nitrogen-fixer to owe its Florida presence to services as a green manure and cover-crop.
Not really a great crop, because the foliage and especially the seeds bear a toxic alkaloid lethal to livestock. The poison renders feeding butterfly larvae toxic to their predators, and serves in some folk medicines against varied complaints, such as intestinal worms. (Poisons are useful for that!)
Crotalaria is a big genus (over 500 species), well represented in Florida by several native and introduced species. Look for yellow pea-type flowers and inflated pods with rattly seeds inside. Rattlesnakes come from the genus Crotalus. Showy Rattlebox has especially large striking flowers and simple (not compound) leaves. It is the only large imposing local Crotalaria with simple leaves.
Showy Rattlebox is native to India, Pakistan, and neighboring regions, and has become a widespread weed warm-climate-globally. This is one tough cookie—full blazing sun, thin soils, sand, marl, rocks, and roadsides. It may be a weed, but railroad tracks would be uglier without it.
One thing I like about Showy Rattlebox is the way the big easily manipulated flowers demonstrate a pollination mechanism found in many legumes having pea-type flowers. Such blossoms have 5 petals: one is the showy banner rising above and behind the others; two side-petals are called wings, and they look like two hands clasped in prayer. To the inside of the clasped hands are two more petals fused into a vertical envelope called the keel. The pollen-bearing stamens and female pistil lie inside the keel like the letter in an envelope.
Here are two great drawings of a similar flowers: CLICK
And CLICK again.
In some legumes, including Crotalaria, the keel looks like Aladdin’s lamp, completely sealed except for the genie exit-hole at the end of a narrow neck. The style and stigma (pollen-receiving surface) are in the form of a narrow fuzzy shaft. The stigma is the tip of the shaft just above the fuzz. Contained within the keel, the anthers deposit their pollen onto the fuzzy region on the style.
When a pollinating insect lands on the top edge of the keel the bug’s weight causes the style and stigma to pop up like the genie rising from the lamp. The protruding stigma snags any pollen on the underside of the visitor, and the fuzzy brush “paints” new pollen onto the insect.