Photos of the Week – June 10, 2022

False gromwell, aka marbleseed (Onosmodium molle) is blooming in our local prairies right now and I’ve been out photographing its unique flowers and the invertebrates visiting them. It’s a plant that is pretty widespread and common around Nebraska, especially in the east and north, though not so much in the Sandhills. Cattle don’t tend to graze the plants, so they can be found even in native prairies with a history of overgrazing.

False gromwell (Onosmodium molle). Gjerloff Prairie. Nikon 10.5mm fisheye lens. ISO 500, f/8, 1/800 sec.

Marbleseed is a very distinctive looking plant. Its flowers are particularly interesting looking, and describing them can be tricky. In a way, they look like white flowers that haven’t opened yet. Or maybe like little white sock puppets sticking their tongues out?

The Flora of Nebraska has a much more technical and precise description for those of you fluent in botanical terminology:

“Flowers well developed but not showy; sepals lanceolate, strigose, united at the very base; corolla tubular, 7-15 mm, with 5 erect, acute, greenish to yellowish-white lobes, without fornices; stamens inserted in the upper 1/3 of the tube, the anthers longer than the filaments, included; style long-exserted, persistent; gynobase flat.” – The Flora of Nebraska

I expect that clears things up for you? If not, here are a couple photos that show the flowers up close.

Helzer family prairie. Nikon 105mm macro lens. ISO 320, f/7, 1/800 sec.
Gjerloff Prairie. Nikon 105mm macro lens. ISO 500, f/14, 1/640 sec.

Given the unique shape of the flowers, you’d probably think pollination might be difficult for some species. You’d be right. I mainly see them visited by bumble bees, though I’ve read that honey bees and even some smaller bees can sometimes gain access as well (I’ve never seen that) as well as other insects like true bugs and ants.

Earlier this week, I had the chance to photograph several bumblebees demonstrating their technique for obtaining pollen and nectar from the flowers. All of them were basically just pushing their faces into the flowers and forcing them open. That’s a perfectly reasonable approach if you’re big and strong enough to do that, but it helps explain why many smaller bees don’t seem interested or able to follow suit.

An eastern bumblebee (Bombus impatiens) forcing its way into a flower. Gjerloff Prairie. Nikon 105mm macro lens. ISO 500, f/16, 1/500 sec.
Black and gold bumble bee (Bombus auricomus). Gjerloff Prairie. Nikon 105mm macro lens. ISO 500, f/10, 1/1250 sec.
Eastern bumblebee (Bombus impatiens) pausing to clean off its tongue. Gjerloff Prairie. Nikon 105mm macro lens. ISO 500, f/16, 1/500 sec.

As the ‘marbleseed’ nickname implies, the seeds are hard and round. They’re very similar to those of puccoons, which isn’t surprising since they’re fairly closely related. I don’t know what eats them but I’ve found little caches of them stored in prairie (often exposed by a prescribed burn) that I assume were collected by mice.

According to John Hilty’s excellent Illinois Wildflowers website, there are several insects that are specialist feeders on the leaves, stems, and/or roots of the plant. The abundant stiff hairs, though, make them unattractive to many larger animals, and that avoidance is further enhanced by the fact that the foliage contains toxins (alkaloids). That’s not a bad combination of defense mechanisms.

It’s rare to see thick patches of false gromwell in the prairies I know. It seems to occur as scattered plants, though some prairies do have quite a few of them. I don’t think it enjoys strong competition from other plants or really productive soils (two factors that are correlated). Instead, it’s usually in drier soils or hillsides where growth conditions, aided by large grazers, help limit competition.

We’ve had great luck getting marbleseed to grow in our cropland restorations at the Platte River Prairies and it is spreading in our family prairie too. Apparently, the bumble bees are good at their job and facilitating the development of lots of seeds. I’m glad – it’s a fun species to have around.

Crab spider on the flowers, probably hoping for something a little smaller than a bumble bee to stop by. Helzer Family Prairie. Nikon 105mm macro lens. ISO 320, f/16, 1/125 sec.
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About Chris Helzer

Chris Helzer is the Director of Science for The Nature Conservancy in Nebraska. His main role is to evaluate and capture lessons from the Conservancy’s land management and restoration work and then share those lessons with other landowners – both private and public. In addition, Chris works to raise awareness about the importance of prairies and their conservation through his writing, photography, and presentations to various groups. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press. He lives in Aurora, Nebraska with his wife Kim and their children.

5 thoughts on “Photos of the Week – June 10, 2022

  1. False Gromwell is one of my prairie favorites, such a unique white flower, beautiful in its own way. I’ve run into botanists who favor the old scientific name (Onosmodium molle) because it supposedly translates to “sweet donkey’s breath” and who wouldn’t like that?! The new name is Onosmodium bejariense, but I haven’t a clue what that translates to.

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