What is Amorpha?

Leo Zimmermann
Leo Zimmermann
Man mowing the grass
Man mowing the grass

Amorpha is a genus of flowering plants in the family Fabaceae often referred to as false indigo. The name comes from Greek roots meaning "misshapen." This description results from the fact that Amorpha plants have one petal, unlike other members of this family, which have five. Similarly to other members of the family, Amorpha plants reproduce using seed pods. Most of the Amorpha species grow in the United States, although some range into Canada and Mexico. These plants are eaten by moth larvae, especially Schinia lucens.

Desert false indigo, or indigo bush, is known scientifically as Amorpha fruticosa. This species is sometimes considered invasive, particularly in the northeastern United States. In other places it is actively cultivated. The plants can grow to be about 20 feet (6 meters) high and extremely wide. Much of the mass of these plants is concentrated in their upper third, although shape can vary due to variations in climate and local environment. They typically grow near fresh water. A. fruticosa is probably the most widely distributed member of the genus.

Amorpha nana, or dwarf false indigo, is similar but smaller. Its maximum height is around 3 feet (1 meter). This plant is also called fragrant false indigo because of its pleasant smell. A. nana grows primarily in the Midwest. This plant is somewhat threatened in the wild, but is also a relatively common choice for garden cultivation.

Amorpha canescens, also known as leadplant, is somewhat smaller than A. nana and less widespread. It is found primarily in northern Illinois. Of all the different species in this genus, leadplant is the one associated most with indigenous uses. It most likely had historical uses relieving skin and gastrointestinal pain, along with rheumatism. These plants have deeply entrenched roots and can survive fires quite effectively. The name canescens means 'graying,' and refers to the many small gray hairs covering the plant.

A fruticosa and A. canescens are the most common forms of Amorpha. There are at least 14 other species, many of them rare and limited to small regions. Amorpha ouachitensis, or Ouachita Indigobush, is a threatened species found only in the Ouachita mountains of Arkansas and Oklahoma. Amorpha georgiana, Georgia false indigo, grows only in Georgia and the Carolinas. Herbacea and schwerinii have similar regional distributions. The habitat of Amorpha californica is probably obvious: California.

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