I think I figured out a slightly more reliable way to tell our two trout lily species apart! Here's Erythronium americanum on the right, and the (locally) more common Erythronium umbilicatum on the left.
E. americanum is, on average, bigger, both the leaves and the flowers. I think they might be generally less dappled, but there's so much variation in leaf color that's not very useful. A lot of overlap in size, too.
Once they're done blooming, they're easy to tell apart, by the fruits. E. umbilicatum has a larger fruit with a dimple in the end, shown on the left here below. E. americanum has a smaller fruit with a persistent style, shown on the right.
(Credit for this photo to Will Cook, as it says. I borrowed it from his website at http://www.carolinanature.com/plants/dimpledtroutlily.html)
The better way to tell the two species apart is clearly visible in the pictures at the top: the anthers! Usually (though not always - I didn't say this was foolproof, and plants insist on varying) E. umbilicatum has purple anthers, and E. americanum has yellow. Ta-da!
