Mystery Plant of the Prairie
Do you recognize this plant? Looks like a sunflower, right? But it’s not.
If you like guessing games, ready, Player One! Put your guess in the comment section below — BEFORE you read further! Extra credit for genus and species.
Here’s a hint: if you had been an early settler crossing the prairies of the midsection of the U.S., you would no doubt have been familiar with the plants of this genus: the silphiums. I would probably still be ignorant of it had I not participated in a neighborhood plant exchange about 10 years ago. Incidentally, a plant exchange is a fun and free way to acquire plants, and you just might want to host one yourself. At this particular plant exchange, I took home a plant I didn’t recognize, and the neighbor who contributed it was sorry but she no longer remembered where or how she had obtained it, except that it had been a passalong plant to her as well.
That single plant soon grew into a robust colony, and its clear yellow sunflower-like blooms lasted for long periods in summer and brightened a large area that had been an empty patch of very lean clay (I hesitate to use the word soil in referring to this expanse of red concrete). I loved it, but I didn’t know its name; neither did my neighbor. Research on this plant became a bit of an obsession, and now I’m confident that it is Silphium integrifolium, commonly called rosinweed. Thus began my relationship with the silphiums.
You may have read about the ancient plant named silphion (note the difference in spelling), which the ancients used medicinally for a variety of purposes, including birth control and as an aphrodisiac. That plant was likely a relative of fennel and may now be extinct. In any event, that’s NOT the silphium we’re talking about here; hope you’re not disappointed.
The silphiums are natives of North America. According to the USDA Plants Database, there are 19 species in the genus silphium. The four species we’ll focus on here — the more common ones — are rosinweed, compass plant, prairie dock, and cup plant. Keep in mind that all four are sometimes lumped together under the term rosinweeds due to the sticky resin they exude when stems are bruised. All of these silphiums have sunflower-like blossoms atop tall stems. They seem to be immune to most pests and diseases and are adaptable to most situations so long as they get plenty of sun. Given these characteristics, it’s not surprising that they are capable of taking over a garden. My silphiums have generally been avoided by deer, but now and then I see evidence of browsing.
Silphiums are pollinator magnets, attracting a wide variety of insects and native bees. For this reason alone, these plants would be worthy of consideration, even if they lacked those large yellow flowers atop their giant stems.
Silphium Integrifolium (rosinweed, whole leaf rosinweed)
All silphiums are tall, but S. integrifolium is the shortest of the lot at 2-6′. Still it seems like an architectural giant in my garden. The Blandy Experimental Farm operated by UVA has this plant in its meadow, and its website states that it “probably came in with meadow seed” and that it’s a “midwestern species.” It may not be native to Virginia, but since our weather in recent years has see-sawed from one extreme to another, perhaps a plant that’s adapted to the extremes of the Midwestern prairies is just what’s needed.
Silphium integrifolium has been identified as a “problem solver” plant for erosion control by the Missouri Botanical Garden, and also one of three silphiums recommended for “prairie gardens” and dry meadow gardens. I second that, but I would also note that my rosinweed — like many, apparently — has a tendency to flop after reaching its full height. I find this to be another mystery; perhaps you have a clue; if so, please let me know.
Silphium perfoliatum (cup plant)
The cup plant — a Virginia native — does indeed have a cup-like feature, and it can actually hold rainwater, a feature appreciated by hummingbirds. Another feature is its square stem, around which the leaves meet to form the cup. Those stems reach heights of 4-8′. It grows best in full sun with wet to moderate moisture. Because it has a tap root, it does not transplant well except when quite young.
This species prefers a moist soil. In its native habitat, Silphium perfoliatum is found in damp areas, such as along prairie streams and ponds, though it can apparently tolerate clay. I’d love to grow this one, but my gardens are dry, not moist. Here’s what the Missouri Botanical Garden has to say about garden uses for this plant:
“A large plant that needs lots of space. Some gardeners find cup plant to be too large and weedy for border rears, but others find it to be an effective backdrop for other perennials. Adapts well to prairies, wildflower/native plant gardens, naturalized areas or moist, open woodland areas including stream/pond edges.”
Silphium laciniatum (compass plant)
The compass plant’s leaves have a north-south orientation, so it does indeed function like a compass! In fact, early settlers crossing the plains used it as a compass. There’s a biological reason for this: the plant’s leaves arrange themselves north and south to avoid the heat of the sun at midday. The leaves are very deeply divided; thus, the species name, which is Latin for “torn into divisions” or “slashed.” The flowers bloom only on the upper parts of the plant and it ranges in height from 6-8′.
Silphium terebinthinaceum (prairie dock)
Prairie dock has multiple flower heads on bare stems, with leaves almost entirely at the base, an unusual silhouette for a silphium. The leaves are large, triangular-shaped, with a heart-shaped base, and large coarse teeth. Those tall, leafless stems can reach as high as 10 feet. Because of its unusual large leaves, this silphium has been called the hosta of the prairie.
In the photo below, the large basal leaves are prominent on a large swath of prairie dock that is not yet blooming. The species name, terebinthinaceum, means “like turpentine,” probably a reference to its resinous juice. Prairie dock is usually found in limestone prairies of the central plains. It can be slow to establish due to its taproot and may not flower until the second or third year.
Are Silphiums a good idea for your yard?
These prairie natives have so many appealing traits — they’re adaptable, easy to grow natives not bothered by disease and pests and they are a boon to many native bees and other pollinators. But some gardeners consider them to be bullies.
As mentioned previously, Silphiums can be aggressive spreaders. Sometimes that can be a good thing, like when you’ve got a large area you’d like to fill. But it might be too much of a good thing, which is what’s happening in New England, where silphium perfoliatum has spread into natural areas and pushed out native New England plants.
Silphium perfoliatum is native to large areas of North America — from southern Ontario through the mid-western and southeastern United States. It was apparently intentionally planted in New England as a “native” of North America, but it now has a listing in the Invasive Plant Atlas of New England. www.eddmaps.org/Center for Invasive Species and Ecosystem Health/ U. of Georgia. There seems to be a cautionary tale here.
As much as I love my rosinweed, I would have to say that Silphiums are probably not the ideal candidate for every garden. Try it in a remote area of your yard or use it in a meadow garden or for erosion control, where its colonizing tendencies are welcome. And if you have an area that can only be described as red concrete, bring it on!
Silphium Plant Profile, USDA, Natural Resources Conservation Service, https://plants.usda.gov/core/profile?symbol=SILPH
“The Four Silphiums,” Friends of the Eloise Butler Wildflower Garden, https://www.friendsofthewildflowergarden.org/pages/gentian/newarticles/foursilphiums.html
“Silphiums: Four Pillars in the Tallgrass Prairie,” Dyck Arboretum, http://dyckarboretum.org/silphiums-four-pillars-tallgrass-prairie/
University of Illinois Extension, http://extension.illinois.edu/hortanswers/PlantDetail.cfm?PlantID=878&PlantTypeID=14
Silphium perfoliatum, PlantFinder, http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=g650
Silphium terebinthinaceum, PlantFinder, http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=f590
Silphium integrifolium, PlantFinder, http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=277469&isprofile=0&
Silphium laciniatum, PlantFinder, http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=f580