Heliopsis vs. Helianthus (Indiana)

I have noticed that Heliopsis helianthoides observations on iNat often get ID'd to Helianthus, especially by the computer vision. It's getting more accurate but I still want to express how I quickly discern them in the field. When a Heliopsis is observed, the most common incorrect ID's that I see from the computer vision are some of the woodland sunflowers (Helianthus decapetalus, Helianthus strumosus and Helianthus divaricatus).

The easiest difference is that Heliopsis has phyllaries that come to a blunt tip: https://www.inaturalist.org/observations/84243086 while Helianthus has "spiky" involucres consisting of sharp-tipped bracts, usually more than one rank: https://www.inaturalist.org/observations/90899588. The flower buds of Heliopsis are quite urn-shaped just before opening. The technical difference between Heliopsis and Helianthoides is that Heliopsis has fertile ray florets but Helianthus has sterile ones.

Other features that I have noticed are that Heliopsis usually has the inflorescence facing straight up, perpendicular to the horizon, while the woodland Helianthus usually have nodding heads that want to face the horizon. Heliopsis often has slightly more orange rays than the woodland sunflowers, but meager individuals can be paler yellow.

Both Heliopsis helianthoides and Helianthus spp are sunflowers that tolerate a wide range of habitat preferences. Heliopsis can grow in shade or sun, in moist to slightly dry ground. Of the three woodland sunflowers mentioned before, H. divaricatus seems to be most adapted to open or savannah areas, the others are typically found in woods. Heliopsis is often used in restoration plantings because it has high germination rates and will often flower the first summer after planting. I will say that the plants that I see in restorations are often quite a bit more vigorous than populations that I believe to be wild, and often have more pronounced inner phyllaries. I attribute this to the affects of breeding plants at an industrial scale--the more vigorous plants may produce more seed. Indeed, Heliopsis helianthoides is quite variable and this fact no doubt accounts for the low accuracy of iNat's computer vision.

All in all I think it's a good skill to have to be able to discern the two genera from a distance, and to sum up the difference in one picture each, we have Heliopsis https://www.inaturalist.org/observations/193353872 and Helianthus: https://www.inaturalist.org/observations/146857938 (the color might be slightly exaggerated in the Heliopsis image).

Posted on February 07, 2024 02:24 AM by danlego danlego

Comments

Excellent insights, thank you for sharing.

Posted by kent_ozment 6 months ago

That’s great info, Dan!

Over the years, I’ve devolved to assuming that any forest-edge sunflower-like plant I see is either False Sunflower or Woodland Sunflower. When this is true, they are pretty easy to tell apart at a glance just from the differences in leaf morphology. But, it may not always be true, so I might be missing some other Helianthus species growing in the area. I will use your info as a guide to look closer at these plants.

I’ve been attempting to propagate both species from seed over the last couple years. False Sunflower definitely is easier. It generates many more seeds and larger seeds than Woodland Sunflower. I would guess that its rapid growth and reproduction cycles also makes it more tolerant of deer herbivory.

In the wild, I’ve noticed that False Sunflower seems to be more common in lower, moister areas (hollows), whereas Woodland Sunflower seems to be more common in dryer upland areas (ridges). But, I live on a ridge and the False Sunflower I’ve planted here seems to be doing just fine. So, the difference in the wild may be a result if different historical land-use impacts. It’s probably harder for a plant species like this to move back uphill after it’s been wiped clean from a ridge by failed attempts at farming (i.e. most of upland Brown County).

Posted by rossberryhill 6 months ago

Good points. Yes, false sunflower is downright weedy in my garden beds and I have one plug of woodland sunflower that is now a couple years old. I think seeing them in a garden, especially when you can pluck and look at them side by side it makes the differences much more obvious.

One thing I should also have mentioned in the original post is that Heliopsis will bloom for a much longer period in total than Helianthus usually will.

Posted by danlego 6 months ago

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