Home of the Practically Perfect Pink Phlox and other native plants for pollinators

Wednesday, August 28, 2019

Wildflower Wednesday: Wild Senna

 Senna marilandica, Senna hebecarpa

Let me be absolutely honest with you from the start. I have no idea if my plants are Senna hebecarpa or Senna marilandica. For many of us they're indistinguishable from one another until their seeds ripen. The pods look the same, but they behave differently, Senna hebecarpa seeds will be expelled from their pods, while the seeds of Senna marilandica will stay tightly enclosed within the seed pod for months. I'll come back and relabel this post as soon as I know which Senna I have.

In the meantime, our Wildflower Wednesday star will be known as Wild Senna, the beautiful.

Wild Senna is a perfect plant for any gardener who loves pollinators, especially lovers of the bumbles. It seems that bumbles are picky eaters and prefer plants with nutrient-rich pollen. Wild Senna is one of their preferred pollen sources.

How do I know this?

 A "2016 study by researchers at Penn State found that bumble bees preferentially visit flowers that produce pollen that has higher protein-to-lipid ratios, and wild senna was the favorite of bumble bees amongst the plants used in the study." In case you're curious,
spiderwort and Culver's root were also among the highest visited plants in the study.

Wild senna is a member of the Fabaceae/pea family and native to eastern North America. Long lived and tall (could be 7 foot) it prefers sun/part sun and uniformly moist soil to thrive. Our star has flowers that are unusual for a member of the Pea family. Rather than curling to form the banner, wings and keel that are common Pea family characteristics,Wild Senna’s petals are open and distinct. It does have other characteristics that make it standout as a Fabaceae family member: pea like pods and compound leaves.

Bumblebees and sweat bees are favorite visitors, although, bumbles are the primary pollinators for Wild Senna. Bumbles visit for the aforementioned nutrient rich pollen. The collected pollen feeds the growing larvae and provides provision for the long winter.

Like Partridge peas, Wild Senna does not produce nectar in their flowers, instead, the 'nectar' is found in little bulbous growths at the base of each stem called an 'extrafloral nectary'. These nectaries attract ants, flies, wasps and beetles. Occasionally, butterfly visit them. So far, I've only seen these large ants and a few smaller ones. I've seen seen Cloudless Sulphur butterfly flitting about the garden, but, I've not seen them on the Wild Senna. Which surprises me, since Wild Senna is a host plant for their cats.

It's a great plant with excellent wildlife value. 
There's only one problem with Wild Senna! It doesn't bloom nearly as long as I want it to! But it does have height, good looking compound leaves and blooms exactly when Bumbles need the pollen the most....Late summer when many are provisioning their nests for winter (especially in gardens further north of me).

aren't the seed pods cool
The flowers give way to pendant, pea-like seed pods which turn black in fall and are either expelled (if S hebecarpa) or persist (S marilandica) on the plants after the plant has died back to the ground in late fall.

I think the plant in seed is a beautiful as in flower.

This is a plant that belongs in every garden, especially pollinator gardens. I've only seen it offered online (most often as seeds). It's frustrating to see the same old same old perennials at nurseries when there are fantastic native plants that make the most sense for our gardens...but, I digress.

I've been imagining it as a replacement for the notorious Forsythia  Hedge (slowly removing). I can see it now, Wild Senna with it's beautiful compound leaves and stellar butter yellow flowers with Panicums, Indian Grass, Verbesinas, New York Ironweed, Joe pye weed, Boneset, and the ex-Asters. Note that all those plants prefer moist soil, which I don't have, but, oh doesn't that sound like a beautiful garden bed? 

This fall, I will sow seeds near the ex-asters and the Texas Star Hibiscus (they're located on a soaker hose route). I think they will dance well together. What do you think of planting  Packera aurea at it's feet for spring color?

Which ever Senna this turns out to be, it's so very welcome in my garden.


The Particulars

Family: Fabaceae
Common Name: Wild senna
Botanical Name: Senna hebecarpa or Senna marilandica
Distribution: Senna hebecarpa is native across the Northeastern U.S. from the Great Lakes as far south as Georgia. Senna marilandica has a broader range extending further west and south. It is generally found on disturbed sites, moist meadows, pastures, fields or roadsides in full or partial sun. It often flourishes within the floodplain of rivers. While it prefers moist soils it will also grow on dry sites.
Light Requirements: Full Sun, Half Sun/Half Shade

Soil: tolerating wet and dryer soils (once established) 
Flower: Small butter-­‐yellow flowers that grow in a profusion at the top of the stems.
Height: 3 to 7 foot tall
Bloom Time: July and August in middle Tennessee, I hope into the fall
Fruit: Senna marilandica~pendant, pea-like seed pods (to 4" long) which turn black in fall and persist on the plants well after the plant has in the normal course died back to the ground. Senna hebecarpa The dark brown seedpods are about 10 centimeters long when fully mature in September – October. The seed pods have 10 – 18 segments and split explosively when ripe.
Host Plant: Cloudless Sulphur, Sleepy Orange, and Little Yellow, Ceraunus Blue and Gray Hairstreak  caterpillars. A good nectar source that also attracts many pollinators in addition to butterflies. 
Companion planting:  Switch Grass, Indian Grass, wingstem, New York Ironweed, Joe pye weed, Boneset, Asters. To be sure you have good color in the Spring you can use golden Groundsel which flowers in late May into June. Wild Senna is an excellent plant for a wet meadow planting or garden border. Put it in the middle or rear of the bed.
Range: Senna hebecarpa is native across the Northeastern U.S. from the Great Lakes as far south as Georgia. Senna marilandica has a broader range extending further west and south.
Comments: Is not grazed by mammals.

****I declare that our wildflower star star is Senna marilandica!****
 The seed pods are the giveaway to me!
Welcome to Clay and Limestone's Wildflower Wednesday celebration. WW is about sharing and celebrating wildflowers from all over this great big, beautiful world. Join us on the fourth Wednesday of each month. Remember, it doesn't matter if they are in bloom or not; and, it doesn't matter if we all share the same plants. It's all about celebrating wildflowers. Please leave a comment when you add your url to Mr Linky.

Gail Eichelberger is a gardener and therapist in Middle Tennessee. She loves wildflowers and native plants and thoroughly enjoys writing about the ones she grows at Clay and Limestone. She reminds all that the words and images are the property of the author and cannot be used without written permission.


  1. I love the pods of this flower, have never seen it before

    1. it is pretty. Those pods are like fireworks.

  2. I have both, and am thinking I have it figured out which is which. I think it is the hebecarpa that blooms before the other. The seed pods on it are smoother. The marilandica pods are kind of "hairy". I will watch to see which ones let the seeds go. I do have loads of volunteers, and have no idea if they are one kind or both. I recently found out they are poisonous, so am deciding not to let as many new ones that come up grow.

    1. I think it's S hebecarpa, too, but, wanted to be sure...

  3. That plant is new to me and it's a beauty :) xxx

  4. Those bright yellow blooms and seed pods make sennas a great additions to the garden. You've reminded me I had Lindheimer's Senna at one time and need to find seeds to get it back.

  5. I am posting this for a friend who had trouble posting. "Great article, Gail. I didn't know the seed ejection was so different between the two. Based on the picture that shows the legumes, I would say the plant is Senna marilandica based on the seed chambers that are about twice as wide as they are long. In S. hebecarpa, I think the chambers are almost square. Not sure; just a thought. Let us know how it turns out.”

  6. Fabulous flower! It grows along our property line and the pollinators love it. I am working on my post. It might be Thursday or Friday before I get it up but I'm working on it.

  7. Great plant! I just added some this summer. Hopefully the rabbits won't eat it.

  8. I have admired this plant for some time. I have tried to grow it so many time and finally last year I guess I found the correct spot. It came out this spring, we had an exceptionally wet spring and summer. It has taken hold and I hope it continues to do so. I have found so many bumbles on those blooms. I didn't know they were going for the bases of the flower. You always have interesting information to go along with your subjects.

    1. Great news, Lisa. So glad it settled in. It's fun to find interesting things out about plants.

  9. Beautiful photos, and interesting information!
    Thanks for hosting Wildflower Wednesday.
    Have a wonderful weekend!

    1. Loved your WW post! I am going to give BB a try!

  10. I have a butterfly for your pollinators.

  11. I have one Senna hebecarapa. I planted it 3 years ago. Last year it had just a few flowers, I'm hoping it will have a much better floral display this year. Glad to hear that this is a bee favorite.

    1. I love this plant so far and hope it remains happy here...Here's to more flowers on yours.

  12. Gail, I was certain that you had Senna marilandica based on the flower photos. Quoting John Hilty's Illinois Wildflowers website, "The flowers of Maryland Senna have styles with short appressed hairs, while the flowers of Wild Senna have styles with long spreading hairs." This is fairly obvious in the field, because the style of Maryland Senna appears greenish while the style of Senna hebecarpa is white and fuzzy due to the spreading hairs. The white would stand out in your first photo if you had S. hebecarpa.

  13. I am in San Diego and I just came across your article. Today my "Butterfly plant" thats what I call it, bloomed for the first time revealing a beautiful 5 petal yellow flower and a curious upswept green pistol that I now believe to be a wild Senna. It has small leaves no more than an inch accross and 2.5 inches long with a peppery smell when cut or trimmed back. I have kept it only because it brings yellow butterflies to the yard.


"Insects are the little things that run the world." Dr. E O Wilson