Sunday, May 27, 2012

False Indigo Bush

A few days ago, when I was walking through one of my local birding spots, I noticed some medium-sized shrubs with compound leaves. What stood out most were the spikes of dark purple flowers at the tip of each of the branches. Despite the showy flowers, I could not remember having seen these plants before. After taking photos and searching through some plant references, I came up with a name: False Indigo Bush (Amorpha fruticosa), also known as Desert False Indigo. Since finding this patch, I have been seeing false indigo all over the place, which makes me wonder how I had ever missed them.

When I saw the compound leaves, I guessed that the shrub probably probably belonged to the legume family (Fabaceae), which turned out to be correct. (Legumes are not the only plants with compound leaves, but something about the smooth leaflets reminded me of other legumes, especially locust trees.) Shrubs in the genus Amorpha are unusual in having flowers with only one petal, curled into a tube out of which the reproductive parts emerge. A standard pea flower looks more like this, with a banner, keel, and sometimes wings. The single petal of an Amorpha flower is the reason for the genus name; it means "formless" or "deformed" in Greek.

False Indigo Bush is adaptable to different soil types and grows quickly. While it is native to North America, it is considered weedy or invasive in the northeastern and northwestern parts of its range, where it probably spread through escapes from cultivation. However, it does provide food to many insects, as foraging habitat for native bees such as mining bees and sweat bees and as a larval host plant for Silver-spotted Skipper, Southern Dogface, and other butterflies and moths.