Sometimes you look right through it
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| slimflower scurfpea, Pediomelum tenuiflorum |
Sometimes its the green clump in the brown grass
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| slimflower scurfpea, Pediomelum tenuiflorum |
Short (rarely more than 2' tall), with small leaves pea-like, small blue-purple flowers, and a difficult name to remember (in English or Latin), slimflower scurfpea, Pediomelum tenuiflorum (pea family, Fabaceae) doesn't get much attention. Yet it is an American native wildflower with a range all across the mid-continental grasslands, from Indiana and Kentucky to Montana and New Mexico (see USDA plants data base under Psoralidium tenuiflorum).
"Scurf" in scurfpea means scruffy, flaking, which describes how the stems and leaves looked to botanists. Pea is for the pea-like flowers, leaves, and seed pods. Slimflower represents its delicate flowers. In its scientific name, pedio means "field" or "plains" and melum is "honey" or "sweet," so the compound "field honey" of its scientific name probably is meant to say "a sweet plant of the prairie" though I have not found a definitive answer. The species epithet tenuiflorum is basically "slim flower", often interpreted as "with few flowers." The name of the first genus it was placed in, Psoralea, means scruffy, so scurfpea is saying "a psoralea-type pea, not a lotus or sweetpea." Psoralidium, another name it uses, is "small psoralea" or, really, "related to Psoralea." A scruffy looking little pea-plant. Not much of an endorsement for a plant I find quite attractive.
It is sometimes called wild alfalfa, which is a pretty good description of it, but that name is also applied to alfalfa that has escaped cultivation (Medicago sativa) and exotic legumes closely related to alfalfa such as black medic, Medicago lupulina, so creates confusion.
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| slimflower scurfpea with flowers and seed pods, hanging down over the trail |
The scientific name of this plant is a mess. For decades it was in the genus Psoralea, a group of several hundred species with a worldwide distribution. Studies in the early 21st century divided the genus up and the name Psoralea was kept by plants in southern Africa. The American species, about 47, were divided. The species of the eastern U.S. mainly went into the genus Orbexilum (9 species) and those on the West Coast into Rupertia and Hoita (3 species each). The midcontinent species were divided betweeen Pediomelum and Psoralidium (23 Pediomelum, 3 Psoralidium). Slimflower scurfpea went into Psoralidium as Psoralidium tenuiflorum. This was in the early 2000s. In 2008 and 2009, more advanced DNA studies found that the plants in Psoralidium were not distinct from Pediomelum and Pediomelum had precedence [botany nomenclature geeks: read Egan and Reveal, I'm simplifying], so slimflower scurfpea became Pediomelum tenuiflorum. The other two species in Psoralidium became Ladeania junceum and Ladeania lanceolata; therefore the genus Psoralidium has no species.
However, just because something is published does not mean everyone reads it and certainly does not mean they agree. A lot of botanists picked up the change from Psoralea to Pediomelium and Psoralidium but acceptance of the demise of Psoralidium is much less. As of today, both the USDA Plants data base and Lady Bird Johnson Wildflower Center call slimflower scurfpea Psoralidium tenuiflorum. My Flora of Colorado has the plant in Pediomelum. The Royal Botanic Gardens at Kew's Plants of the World Online, trying to sort out scientific names from all over the world, says the right name is Pediomelum tenuiflorum and that Psoralidium tenuiflorum is a synonym; a synonym in botany is a name that has been superceded. For now, when looking for this plant, try both Pediomelum tenuiflorum and Psoralidium tenuiflorum.
Slimflower scurfpea is a perennial with a deep tap root. I briefly studied it in Colorado, years ago. I suspect it can live decades because I found plants like the ones pictured below that didn't change size much in three years and would have taken several to many years to reach that size.
Like most legumes, it captures nitrogen from the air and adds it to the soil as it grows, enriching the soil. The result is that slimleaf scurfpea can grow in quite poor soils, as in the photo below.
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| slimflower scurfpea on rocky soil, on a roadside in Colorado: If you look closely you can see the blue flowers |
I cannot find any native insects listed as feeding on it, but that is certainly for lack of study, not because there are none, since it is widespread and often common.
The pea pods on the plant dry out and crack open, but they stay attached. The plant spreads them by tumbleweeding. As the plant dries out, a specialized row of cells across the base of the stem disintegrates making a smooth break, called an abscission layer, that lets the top of the plant break off if bumped. Prairie winds easily pick it up and tumble it--note the plants above tend to have a rounded shape that rolls easily--dropping seeds each time they turn over. Tumbleweeding is a dispersal method that works best in windy regions of low or patchy vegetation. It is very uncommon in the pea family, but works well for slimleaf scurfpea.
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Slimflower scurfpea lodged against a fence at the edge of a tallgrass prairie in Nebraska. Tumbleweeding plants tend be caught by fences |
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| 1980s photo from Konza Prairie, a tallgrass prairie in Kansas: See the upsidedown slimflower scurfpea In a dry year an unburned tallgrass prairie is a good surface to tumble across |
Across its multistate range, slimleaf scurfpea varies in leaf and stem, flower, and pod details, but the variation does not form a pattern that suggests there are really two species, it is just a very variable species.
The genus Pediomelum diversified very recently across North America, during the Pleistocene (Ice Ages), the last 1-2 million years, and slimleaf scurfpea separated from its nearest relatives in one of the most recent splits. This is a plant success story--both Pediomelum and Pediomelum tenuiflorum--spreading and adapting across North America in the aftermath of the glaciers.
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| slimflower scurfpea flowering, quite a big plant |
The Dakota and Lakota drank the roots boiled in water to treat tuberculosis and headaches, respectively. The Ramah Navajo drank the plant soaked in water or smoked it (presumably dried) to counter flu. The Zuni rubbed moistened leaves on the body for purification.
The Ramah Navajo treated sheep troubled by coughs with slimflower scrufpea.
The Lakota burned it to drive away mosquitos.
The Kiowa sometimes turned the stout stem into a fork.
Navajo mask makers smoked slimleaf scrufpea after the feast celebrating the completion of the masks for Night Chant healing ceremony.
Those are all good uses of the plant, but my favorite is that the Dakota wound slimleaf scurfpea plants into head protection. When it was very hot, they wrapped a plant around their heads for sun protection. Moerman calls this "as a garland" but I've been too hot on the prairie and I'd say "as an improvised sun hat." Its a trick I wish I'd known when I was working western prairies in midsummer. The plant smells good and is rather moist, I think putting it around your head is a great idea. I always soaked a bandana, but I had access to a windmill.
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| slimflower scurfpea on the edge of the trail |
Widespread, variable, and pretty: watch for it!
Comments and corrections welcomed.
References
Ackerfield, J. 2015. Flora of Colorado 2nd edition. BRIT Press, Fort Worth, Texas.
Egan, A. N. and K. A. Crandall. 2008. Divergence and diversification in North American Psoraleeae (Fabaceae0 due to climate change. BMC Biology. 6:55, doi:10.1 186/1741-7007-6-55
Egan, A. N., and J. L. Reveal. 2009. A new combination in Pediomelum and a new genus, Ladeania, from western North America (Fabaceae, Psoraleeae). Novon: A Journal for Botanical Nomenclature. 19 (3): 310-314.
Fernald, M.L. 1970. Gray's Manual of Botany 8th edition. D. Van Nostrand Company, New York. Because it made space enough to explain the scientific names.
Kellar, C. L. Jr. and R. Kellar. 2019. Molecular and morphological variation among populations of Pediomelum tenuiflorum (Pursh) A. N. Egan (Fabaceae) in Nebraska, USA. Transactions of the Nebraska Academy of Sciences and Affiliated Societies. 39: 17-37.
Keeler, K. H. 2015. Plant Ecology--Tumbleweed, The Lifestyle. this blog. link
Moerman, D. 1999. Psoralidium tenuiflorum Native American Ethnobotany database. Online version: link (accessed 4/24/26)
Royal Botanic Gardens. Kew. Psoralidium tenuiflorum. Plants of the World Online link (accessed 4/26/26)
Look Twice, containing stories of plants from western Nebraska and eastern Colorado, available from Amazon link or from me. This is part of the unique western Nebraska ecosystem that burned with huge wildfires in March 2026.
And
NoCo Notables, Stories of Common Plants of the Colorado Front Range, Many plants have cool stories, about their interactions with other plants and animals and with humans. Go beyond just having a name for the plant, learn more about it. Available from Amazon link or from me. 
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