Prairie Porn I: The Fabaceae

Prairie Porn I: The Fabaceae

Walt Whitman  wrote the following of the North American prairies "...while I know the standard claim is that Yosemite, Niagara Falls, the Upper Yellowstone and the like afford the greatest natural shows, I am not so sure but the prairies and plains, while less stunning at first sight, last longer, fill the esthetic sense fuller, precede all the rest, and make North America’s characteristic landscape.”
–Walt Whitman, Specimen Days (1879)

Having spent almost my entire summer in Wisconsin's prairies, I couldn't agree more. If it were not for the ubiquitous swathe of agriculture encircling nearly all of the few prairie remnants left in southern Wisconsin, these places may still be the most serene and awe inspiring in the Midwest. But of course the reality is that these communities are dwindling in size and numbers, and a host of exotic plants and animals are forever changing their compositions.
Nevertheless, a great diversity of native plants and wildlife abound in Wisconsin's prairies. Though  our native species may not be as dramatic as those found near the western coast or in the south-eastern wetlands, many are just as beautiful and charismatic.

For the first installment of Prairie Porn, I will focus on the story of the Fabaceae, the pea and bean family. The Fabaceae, like the Asteraceae (which will be discussed in later installments) is one of the most dominant plant families found in the Wisconsin prairies. When viewing a low lying prairie from atop a bluff in late spring and early summer, you will find that the most eye catching floral displays are often produced by members of the bean family.

Baptisia alba, photo courtesy of http://sweetbay103.blogspot.com

Baptisia alba (wild white indigo) sends up fantastic throngs of delicate white flowers on stalks ascending from a dark violet tinged herbaceous stem. This species grows a meter tall, far above the most of the other springtime forbs. Even before flowering, this plant is easily identified by its distinctive three part compound leaf. The only other native Baptisia species is B. bracteata which has a spreading growth form much closer to the ground, and has darker and narrower leaves.







The only other native member of the Fabaceae family that could rival  Baptisia in both height and noticeability is Lupinus perennis (sundial lupine). This striking Fabaceae is characterized by its fantastically blue/violet colored spike like inflorescence. This species is unique among the Wisconsin flora with its distinctive 7-11 parted palmate compound leaves. For those of you who may have missed the two lectures they spent on plant parts in introductory biology, this means the leaf is dissected into a number of individual leaflets, arranged in a spreading spacial pattern similar to how your fingers are arranged about your palm. Like many plant species, Lupinus' genus name is quite descriptive, though as we will see, also quite incorrect. Lupinus is Latin for wolf and refers to the belief that these plants consume or "wolf" the nutrients of the soil in which they dwell. We now know that this is not only incorrect, but the opposite is true which brings us to possibly the most important function of Fabaceae species in the prairie community.

The palmately compound leaves of Lupinus

Lupinus perennis, photo courtesy of Illinois Wildflowers (http://www.illinoiswildflowers.info)

Fabaceae species have an amazing ecological role in plant communities; within specialized structures called nodules in their root systems, members of this family harbor nitrogen fixing bacteria that convert atmospheric nitrogen into a form usable by other organisms, in effect fertilizing the soil around them. This symbiotic relationship is the very reason many exotic Fabaceae species have been introduced to the new world. Crops like corn are especially good at sucking the nitrogen right out of the soil, and so farmers would plant things like alfalfa (Medicago sativa) in a rotation to help restore nitrogen levels in soils that were depleted by other crops. Naturally, Medicago escaped into surrounding areas and is now a common weed in Wisconsin's prairies. Farmers still practice crop rotation, though they are much more inclined to plant round-up-ready soybeans than anything as benign as alfalfa.

There are dozens more native Fabaceae species in a variety of growth forms, all with their own specific characteristics and ecological function and niches. Just to name a few, there is Desmodium canadense (Showy Tick Trefoil) a beautiful pink to purple flowered forb with sticky leaves and seeds, Dalea purpurea (Purple Prairie Clover) a delicate herb with very small leaves and an interesting inflorescence akin to a ballerina's tutu, Apios americana (Groundnut) a mesic/wet species with a climbing vine growth form, and Chamaecrista fasciculata (Showy Partridge Pea) a small and easily overlooked annual forb with highly compounded leaves and beautiful yellow flowers.

Stay tuned for the next installment of Prairie Porn, where I will be highlighting another family of interesting prairie plants!