Allium nevadense is, for the most part, a straightforward and easily recognized species. It has a single, terete leaf, often becoming slightly coiled distally, and white flowers. The tepals are widely spreading, lanceolate, entirely white or occasionally slightly pinkish, sometimes with the midrib a little darker. The stamens are ascending, a little shorter than the tepals, with anthers usually pale pink to yellowish, occasionally darker and reddish. The ovary is prominently crested and pale pink, white, or pale greenish-white.

Going by a 1992 paper by McNeal along with the Jepson eFlora and Flora of North America, Allium atrorubens var. cristatum can be distinguished from Allium nevadense by bulb coat features and by having erect, pale pink, dark-veined tepals. Some Allium atrorubens var. cristatum fits this description admirably. The flowers may be as pale as Allium nevadense when they open but quickly darken afterward. These plants are trivial to distinguish from Allium nevadense. As you can probably guess, some Allium atrorubens var. cristatum looks very much like Allium nevadense and is difficult to distinguish. These plants seem to be most often observed around the White Mountains. We could probably rely on geography to resolve this—but, as mentioned previously, that’s not any fun.

There is still a difference in the angle of the tepals and stamens between Allium nevadense and these troublesome individuals of Allium atrorubens var. cristatum, but it is subtle and I doubt it is reliable in practice. McNeal suggests we might look at the crests of the ovaries, deeply notched apically (i.e., near the style) in Allium atrorubens var. cristatum, usually not deeply notched in Allium nevadense. The ovary crests of Allium are often obscured or difficult to make out in photographs, but the open flowers of these plants make it easier. Of a half-dozen observations of Allium nevadense on which I could make out the crests reasonably well, all appeared deeply notched. Perhaps I could make out a distinction with the two in hand and a microscope, but the brief trial with photographic observations was not encouraging. However, I noticed a much easier feature that appears to be reliable. Allium nevadense has a green nectary ring between the ovary & bases of the filaments and the bases of the tepals. Unless a photograph is particularly oblique—not encouraged by the geometry of these plants—it is apparently always visible. In Allium atrorubens var. cristatum there is no nectary ring—or, at least, none that I can make out in any of the photographs available to me.

So, there you go. If the tepals are erect and pinkish, it’s Allium atrorubens var. cristatum. If the tepals are spreading and white or very pale pink, check for a green nectary ring. Allium nevadense if present, Allium atrorubens var. cristatum if absent.