The Not-so-subtle Senna

Yellow, yellow flowers everywhere. Walking a familiar part of the trail, my eyes scan the usual floral sights of late July: the Silphium brothers Cup Plant (big brother) and Rosinweed (little brother); inspecting the Gray-headed Coneflowers for Camouflaged Loopers...hello, what's this?

My brain, seeing the shape and color of the bushy yellow inflorescence, quickly said "Showy Goldenrod, nothing unusual, move along" followed immediately by "isn't it a little early for goldenrod?" and directing the eyes back for a closer look. 

Bees and ants visiting
senna flowers.

Despite the initial vague resemblance...definitely not a goldenrod. For one thing, the leaves are compound, with tidy paired leaflets. And the yellow flowers comprising the showy inflorescence were big and blowsy, with many dark anthers projecting from the loosely open petals. A senna! Has that been there all these years and I've just never noticed it before now? It's hardly a subtle plant.

There are two similar species of senna in our area, which can be tricky to tell apart: Maryland Senna (Senna marilandica) and American or Wild Senna (Senna hebecarpa). Some points mentioned to help identify are the hairiness of the style (longer on Wild Senna) and the behavior of the seedpods. (I am not confident in our senna here so I will just call it a senna.) 

Knob-like nectaries are situated
at the base of leaves.

They are members of the legume family and are native to the eastern U.S., with Maryland Senna having a slightly wider range, reaching Nebraska and points south. All those stamens (ten in total) provide pollen to bumble bees (and many other pollinators). 

If you look closely at the base of the leaves, you'll find a curious rounded knob: an extrafloral nectary, which makes sweet nectar available to ants, wasps, ladybird beetles, and other insects that may take advantage of the nourishment, possibly providing protective services to the plant in exchange. (Another yellow-flowered native legume, Partridge Pea, similarly provides nectar in the form of little pots at the base of the leaves.)

It's a beautiful plant, and provides a lot of interest not only to wildlife but human observers too. I'll definitely be keeping an eye out for it in the future. 

Really...not very subtle.

Sources/Additional Reading:

• Plants For Pollinators: Wild Senna
• ‘Will Work for Food’ – Extrafloral Nectaries
• USDA Plant Fact Sheet: Wild Senna
• Illinois Wildflowers: Wild Senna and Maryland Senna
• BONAP
• North Carolina Extension: Senna marilandica
• Friends of the Wildflower Garden: Wild Senna

Ratibida Reverie

Today we're taking a field trip about a mile due west of the Greenway, to Terry Trueblood Recreation Area, where you might encounter a few small patches of Ratibida columnifera, known variously as Mexican Hat, Upright (or Longheaded) Coneflower, and Prairie Coneflower—the second of only two species of Ratibida found in our area (and only four found in the entire U.S.).

While the Gray-headed Coneflower (R. pinnata) is native to the tallgrass prairie and widespread throughout Iowa, its low-growing cousin actually hails from out west in the Great Plains, with only the eastern edge of its range just reaching western Iowa. It is adapted to drier conditions than R. pinnata and probably finds the sandy area around TTRA more amendable than the Greenway's moist soils.

You can tell the two species apart by the shape of the flowers (although the photo above and at right is a slightly stunted specimen): R. columnifera's "cones" are usually longer than its wide yellow petals, whereas R. pinnata's yellow petals are longer and thinner beneath a shorter, more rounded "cone". 

Left: Ratibida columnifera. Right: R. pinnata

The leaves and growth habits reflect the habitat preferences of each plant as well: R. columnifera's skinny, hairy leaves help minimize water loss and exposure to the hot sun; R. pinnata's leaves are wider and while also a bit hairy, not as densely so. And much as the prairie transitions from the tallgrass in the east, with its abundant moisture, to shortgrass in the arid west, the tallgrass species Ratibida pinnata can reach 4-5 feet tall while R. columnifera tops out around 3 feet. 

Mexican Hat comes in different forms: its petals may be solid yellow, solid dark red, or dark red with yellow at the edges. Given its natural range, those individuals you find in our area are likely planted specimens from a seed mix or as garden ornamentals. They can be visited by bees, butterflies, and other insects, similar to Gray-headed Coneflower.

Cultivated R. columnifera (from the author's garden)

Sources/Additional Reading:

• http://www.illinoiswildflowers.info/prairie/plantx/mexican_hat.htm
• https://bonap.net/Napa/TaxonMaps/Genus/County/Ratibida
• Midewin National Tallgrass Prairie - Resource Management (usda.gov)