Normally I'm not one for cultivars but I made an exception in this case. I've had Trout Lilies growing in the garden for almost 10 years now and they have yet to flower! Erythronium americanum much prefers to clone itself under the soil sending up a small carpet of roots everywhere. I've ready that on average only 5% (of what might be considered individual plants) in a given population will flower. Blooming seems to be triggered by the tap root finally reaching a certain distance down, or perhaps because it's become stressed from hitting rocks and things. I've been told that they're more likely to flower if rocks are placed just under the bulb to help stress the plant into sending its energy elsewhere but have yet to try this.
So I bought a cultivar called, Erythronium 'Pagoda' which is a hybrid of two species native to the western United States. I gather both are better about flowering and this hybrid cultivar seems to be no exception. It's parents are E. revolutum and E. tuolumnense.
E. revolutum goes by Pink Fawn Lily, and seems to show through in the cultivar by the matting on the leaves. E. tuolumnense goes by Tuolumne's Fawn Lily, and seems to show through in the flower color (yellow).