Desert Fabs

Fabaceous plants, that is. For the next several weeks I’m likely to be posting back-and-forth between finds in Anza-Borrego and in the Maryland piedmont.

Astragalus crotalariae
Salton milkvetch

Astragalus is the largest genus of plants known, with about 3,000 species, around 350 of which are native to North America. A. crotalariae has a limited range, found only in the Sonoran desert, in Northern Mexico and a few parts of southern California and southwestern Arizona. It’s a perennial that grows to about two feet tall.


Lupinus arizonicus
Arizona lupine

There are about 200 species of lupines worldwide, with maybe 70 or so in California. It’s hard to say how many are in the Sonoran Desert, since many of the species have multiple subspecies. A quick glance at several internet sources leads me to think that maybe there are one to two dozen.

L. arizonicus is native to the Sonoran and Mojave deserts. It’s a desert ephemeral, growing only in years when there’s been enough rain, and reaching to about a foot and a half tall, Depending on which authority you consult there are several subspecies; interestingly, several of the subspecies have their own varieties, for example Lupinus arizonicus ssp. arizonicus var. arizonicus and Lupinus arizonicus ssp. arizonicus var. barbatulus. I have no idea which one is pictured here.


Lupinus sparsiflorus
Coulter’s lupine

I found a long swath of these southwest of Borrego Springs, on the other side of the mountain range just outside Azna-Borrego Desert State Park proper, along the shoulder of San Felipe Road. I wasn’t sure at first if they were Arizona lupine or one of the other species.

The color was different, but that’s an unreliable characteristic. The plants were shorter and smaller overall, but that could have something to do with local growing conditions. Then  I found a good description of both species. L. arizonicus has mostly glabrous (smooth) leaves, while L. sparsiflorus is ciliate (hairy), especially at the margins.


Psorothamnus schottii
indigo bush, Schott’s dalea

This six foot tall shrub has a similar range to the Astragalus (that is, rather limited parts of the Sonoran Desert). When it blooms it’s just covered in lightly fragrant blue-purple flowers. And bees.

A Beautiful, Useful Pest in Iceland

Lupinus nootkatensis
Nootka lupine, Alaskan lupine
Icelandic: Lúpína
Fabaceae

 

My recent post about yellow flag iris (“A Beautiful, Useful Pest”) was written in the lounge at Dulles International Airport while I waited for my flight to Iceland. It struck me as funny, then, that the next day, when we parked our rental car near a trailhead and started hiking, that the first flowers I noticed were the Nootka lupines. They were everywhere – wide swaths of blue-and-white flowers ascending the slopes of Mount Esja.

There was so much of it, I wondered if it was an alien invasive. In my limited experience, it’s unusual for native plants to form such massive colonies. Was this another beautiful, useful pest?

Short answer: yes. It’s native to the coastal areas of northwestern North American, and is alien to Iceland. But it didn’t sneak in via packing on a cargo ship or by hitchhiking on other agricultural material. It was introduced, possibly as early as the late 1800s (I’ve read conflicting stories), and certainly by the mid-1900s, when it was planted deliberately and extensively by first the Icelandic Forestry Service, and later by the Soil Conservation Service, to help with land reclamation.

 

You may recall from the previous post that after Icelandic settlement, deforestation and overgrazing led to lifeless soil, which is easily eroded and transported by winds. The Nootka lupine grows fast and roots well, keeping soils in place. It’s perfectly suited to Iceland’s cool, wet growing conditions. And like most members of the Fabaceae (pea family), it takes nitrogen from the air and fixes it in the soil, which together with decaying plant material (from dead lupines) results in soil fertile enough for native plants to colonize. It’s even thought to have helped with the problem of sandstorm-induced road closures in the eastern parts of the country.

But (of course there’s a “but”), it’s too aggressive. It grows tall enough to form a canopy that blocks sunlight to mosses and lichens (which are important pioneer species). It can invade nearby plant communities, outcompete the natives, and form monocultural stands. So yes, it exhibits the usual alien-invasive characteristics.

There’s a little more good news, though: studies have shown that in some sites, lupine colonies will eventually decline to the point where they no longer out-compete other species. It seems that if managed correctly, the Nootka lupine will continue to be a valuable tool for soil reclamation.

lupines on the lower slopes of Mt. Esja


for more information:

Biological Diversity in Iceland (The Icelandic Institute of Natural History; go to page 10 for the case study of Nootka lupine)
Alaskan “Wolf” Invades Iceland (Reykjavik Grapevine, August 25, 2011)
Invasive purple flower Impacts Iceland’s Biodiversity (mongabay.com)
Invasive Alien Species Fact Sheet (nobanis.org)