Journal archives for February 2024

February 07, 2024

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: while Helianthus has "spiky" involucres consisting of sharp-tipped bracts, usually more than one rank: 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 and Helianthus: (the color might be slightly exaggerated in the Heliopsis image).

Posted on February 07, 2024 02:24 AM by danlego danlego | 3 comments | Leave a comment