The right name for Amorpha

There are many species of Amorpha. The species I most recommend to clients, and in my published works, is A. fruticosa. This is because it is hardy in much colder regions, and grows taller -hence producing more biomass, than most species.

It is also the species that is best known worldwide. Several varieties have been bred from it making A. fruticosa one of the best foundational N-fixers on which to build gardens of lush fertility.

The fact is many of the Amorpha in Mortal Tree came from a company that listed the plant as A. californica, not fruticosa. I’ve called it that after I personally identified it. Allow me to explain:

Amorpha californica, according to the literature, grows a maximum of 6 ft. tall, and is only hardy to USDA zone seven. I’m in zone five, where this plant has lived through winters that fully reach the limit of what this zone offers, without the slightest dieback. I also find the Amorpha I have quickly pass up six foot tall. I looked into this further by researching the USDA Plant Database. Here I found information that backed my theory, and even pictures of the different seeds, which look nothing alike. Mine resembled fruticosa. I took liberty of calling the plant what I thought it was ever since.

A. californica seed to the left, A. fruticosa seed to the right. Images from the USDA database.

I still have not the slightest doubt this Amorpha is Amorpha fruticosa. I don’t make such decisions lightly. My rather bold statement in Growing Amorpha that the company had incorrectly identified the plant got me more flack than I had ever expected.

My motive to make this statement was of course to dispel any fears the plant this company is selling won’t live for them if they are in zones 6 and 5. They are a major supplier of this plant, and I am telling people left and right to get it. I did try twice to contact the company to talk about this discrepancy, but their contact system never worked. I figured a small blog like myself was obviously of no consequence in their minds, but I was wrong.

The owner of the company was quite skeptical of my deduction. I was quite surprised when he showed skepticism of even the USDA’s accuracy, since the pictures clearly showed the seeds were not A. californica. He was in fact skeptical of most of the internet’s images of A. fruticosa seeds when I brought them up as examples. The only authority he considered trustworthy was none other than Gerd Krussman’s Manual of Cultivated Broad-Leaved Trees and Shrubs. This of course had been out of print for years, so I wondered how I would get my hands on the volume that had Amorpha in it. Thankfully, I have connections who graciously brought all three volumes to my desk in short order.

Krussman simply confirmed everything I had read previously about the plant. But we needed to identify this plant down to the very details of the flowers before this could be resolved.

Here are the results:

Krussman’s work was not especially helpful in identifying the seeds. The real detail that sets apart A. fruticosa flowers from californica is the width of the petal, and spots on the californica flowers for what the line drawing shows.

The flowers from my plants grown from the companies seed have especially wide petals I could not even make lay flat without ripping. So I spread it as best I could on a pen tip to show the plush width and lack of spots. I’ll let you derive the ID. It seems quite evident to me.

In our conversation about the plant, there was of course suggestion that we had a hybrid on our hands. If it is, it does not show the attributes of californica in the least. Fruticosa has the broader range, the greater popularity, and most importantly, the greatest utility for sustainable agriculture systems. I hope what I have done helped someone find success in this blossoming branch of agriculture through confident use of this amazing plant.