I'm bad about letting volunteer plants grow at their whim if they look like they might turn out to be something worthwhile, but sometimes it pays to grow a few weeds to help you cheat through the dull days of the garden.
A native Kansas annual that grows everywhere I choose to allow it is Euphorbia marginata, or "Snow-On-The-Mountain." Look at the single volunteer at the left blooming in late August in front of the bright red crape myrtle Lagerstroemia indica ‘Centennial Spirit’. Now, I ask you, what better plant combination could you want then this three foot tall spurge growing in front of the five foot tall crape? I counted across the garden this week and I've got over 20 of these volunteers spread out making bright spots over the beds. And look at the flower detail in the picture below. In early September, after a summer's drought and when every other plant has insect or wind damage to half its foliage, look at the crisp, clean margins of these flowers and the white-margined foliage. Green and white may not be everybody's cup of tea, but surely few would argue against the impact of this plant at a time when little else blooms. This relative to the poinsettia has a prolonged bloom period, commonly open from August to October. As an added benefit, this is not a tough plant to pull out from where you don't want it; it may love xerigardening conditions, but the taproot slides right out of the soil when you tug the stem. Just don't get the sap on your hands if you're sensitive.
Snow-On-The-Mountain contains a milky sap that is said to be as irritating as poison ivy on exposed skin. Since I'm immune to poison ivy (how neat is that for a gardener?) and Snow-On-The-Mountain doesn't bother me either, I can't confirm the comparison. One reference said that cattle won't graze on it and if E. marginata is dryed along with hay it can cause sickness and death in cattle. Another says that all parts of the plant are poisonous, so take care with children and don't eat it in your salads.
Now some, of you, I know, are thinking, wait, I have "Snow On The Mountain," and it doesn't look like that. Aegopodium podagraria 'Variegatum', is an invasive ground cover that is also known as "Snow On The Mountain" or "Bishop Weed." It's a variegated perennial, grows well in shade, and doesn't have the milky sap, so you can't confuse the two when you see them . Just another reason for gardeners to bite the bullet, learn genus/species nomenclature and ask for exactly the plant they want when ordering. Seeds are available from several select sources, including Jefferson's Monticello, but look especially for a cultivar named 'Summer Ice' if you can find it, because not all the offered plants have the best bright white margination.
Since my native Euphorbia marginata is identical to 'Summer Ice', I guess I'm just one of the lucky ones.