Hibiscus laevis; Malvaceae (mallow family)
You could hike along the Billy Goat trails all day and never see this flower – but only because the trails never get close enough to the water. Find one of the rocky outcroppings and head out into the river, though, and you’ll see dozens and dozens – or hundreds – of the plants, which can grow to over six feet tall.
They could almost be considered shrubs, as the large stems will get very stiff as if lignifying, and these stems will persist through the winter. But the plant does die back in true perennial fashion.
This rosemallow is a plant that loves to have its feet wet. You’ll find it growing right along the riverbanks; whether or not it’s actually standing in water depends on the water level. The flowers will open to a width of five inches when in full sunlight, then close at night.
Here’s a picture of a smaller plant in bud, showing the leaf shape:
And here’s one more picture, just because:
Elizabeth's Wildflower Blog 