For a number of years, the small flower bed at the top of my driveway has had a mystery plant growing in it.
At first I just cut it down to a couple of feet off the ground so that I could see my street sign number. The plants didn’t grow very tall, and I didn’t see them growing in other garden spots.
As I added mulch and the flower bed developed better soil, the mystery plants started to get taller.
This year, I decided to let everything grow to its full potential so that I could identify what they were, including the mystery plant in the front island.
After reaching a good 7-feet tall, I started to see flower buds branching off the top. Okay, so I had to carefully bend the plant down to see the buds but they were definitely there.
As soon as I saw the yellow flowers, I was able to identify the mystery plant: sawtooth sunflower Helianthus grosseserratus, a member of the daisy family, one of the six large plant families that provide bees and other pollinators like butterflies food throughout the US Midwest growing season.
The Latin name grosseserratus gives a hint to this plant’s description of being a giant herb. The ones on the lower end of this flower bed are growing taller than the ones on the shorter, or left side.
Because they can grow up to 16-feet tall, they do get knocked over by rain storms.
According to Missouri Department of Conservation, sawtooth sunflowers sometimes grow in dense colonies, other times as single specimens.
Lower stems are often hairless, reddish, sometimes with a white waxy coating. Flower heads are all yellow to 3½ inches across, with 10–25 fairly wide ray florets. Blooms July through October, providing pollinators with food during Missouri’s hot August dearth.
The leaves are about 10 inches long and 2½ inches wide, coarsely toothed.
Interestingly enough, sunflowers readily hybridize with each other, which can make identification difficult. Not counting hybrids, there are 16 species of Helianthus recorded for Missouri. This species is perhaps best identified by its leaves, which are mostly alternate, very narrow, folded lengthwise along the mid vein, with flat (uncurled) leaf margins, and yellow disk florets.
I have seen similar-looking yellow flowers but the leaves were different.
Great Pollinator Plant
The Illinois wildflowers website notes “the most common visitors to the flowers are bees, especially long-tongued species. Among these are honeybees, bumblebees, Cuckoo bees (Epeolus spp., Triepeolus spp.), digger bees (Melissodes spp.), and leaf-cutting bees (Megachile spp.).
Other insect visitors include Syrphid flies, bee flies, butterflies, moths, and beetles. Both nectar and pollen are available as floral rewards. Other insects feed on the foliage, plant juices, pith of stems, developing seeds, etc., of sunflowers. These insect feeders include caterpillars of the butterflies Chlosyne nycteis (Silvery Checkerspot) and Chlosyne gorgone (Gorgone Checkerspot), stem-boring caterpillars of Papaipema necopina (Sunflower Borer Moth) and Papaipema rigida (Rigid Sunflower Borer Moth), seed-eating caterpillars of the moths Homoeosoma electella (Sunflower Moth) and Stibadium spumosum (Frothy Moth), foliage-eating caterpillars of Grammia arge (Arge Tiger Moth) and Phragmatobia fuliginosa (Ruby Tiger Moth), and other moths.”
Now that I know what they are, they get to stay. I will move the street sign. After all, who wouldn’t want to claim to be growing a giant herb in their garden that provides for so many pollinators!