While looking for images of impatiens glandulifera sprouts I stumbled on an image of Impatiens pallida. They are extremely similar looking, and the same genus - coincidence? Impatiens pallida is a Michigan native and very common here, I just haven't seen it in this park before - but that makes sense if it washed out of a creek overflow and started a colony here. I guess I will keep an eye on it and see what develops. Thanks everyone !

It appears that Impatiens capensis is more common in Michigan than Impatiens pallida is. Water Hyacinth is a monocot, these seedlings are dicots. They look like capensis to me. The cotyledons of pallida are slightly larger than capensis. Do you have Impatiens glandulifera in your area?

Impatiens glandulifera isn't native here and according to michiganflora.net is only recorded in 3 counties [Alger County, Chippewa County, St. Clair County] 2 of those are in the UP and one near Detroit; I am in Ottawa County, west side of the state, and have never seen it. In some parks Impatiens pallida and Impatiens capensis can be equal in number but in other locations Impatiens capensis will be much more prolific. They both seem to have equal habitats, maybe I. pallida preferring more shaded areas and I. capensis growing in slightly more sunny, or border areas. I just found an image for I. capensis seedling [https://www.minnesotawildflowers.info/flower/spotted-touch-me-not] and both seedlings seem to look almost identical. Since my specimens are just seedlings, they are not likely to flower this year and thus provide confirmation by that means. Thanks for the feedback.

They're annuals, they will flower this year.

Since both Impatiens capensis and pallida are annuals, no reason to think they won't bloom this season!!

Summer droughts always cull them down, and only the strongest survive. I grew Impatiens glandulifera years ago, and it's form was ratty looking in my climate. It didn't spread like pallida and capensis. I figured it couldn't ever become a noxious weed here in the midwest. In the PNW and UK it's noxious, I believe.

That's good news, I should get confirmation later this summer. I will keep you posted.

Here is a follow-up to the sprouts that I spotted back in April. They are not blooming yet, they are in a heavily shaded location, so I can't tell whether they are Impatiens capensis or I. pallida, the leaves look all the same to me. They are turning into a major infestation along the ravine floor. If I finally spot any flowers I will let you know.

Some very fine details are needed to tell them apart. There are orange ones and yellow ones and one of them can be both colors.

I would not call what you are seeing an infestation. It is a natural groundcover layer for the stream side forest habitat, in a disappearing herbaceous annual. That's a good thing. Having said that, impatiens are the #1 summer weed I pull the most of in the wild cultivated gardens.

I called it an infestation because all of this growth is new to this area and appears to have washed into the ravine either by seed or vegetation. You make a good point - it will help control erosion and it is a native species. It just doesn't seem "natural" to this particular location. Lamiastrum galeobdolon also sprung up in another ravine, likely through the same vehicle. I suspect local residents are doing some landscaping and that material is getting into the watershed.

I would call the Lamium in the other ravine an infestation. If it isn't yet, it will be if it grows in Michigan like it does here.

It wouldn't be unnatural for impatiens to colonize an area that may have been recently disturbed. The closer the park is to humans the more chances there are for disturbance, even some maintenance perhaps.