Scilla siberica (Siberian Squill)
In the past I often got Scilla siberica confused with Chionodoxa forbesii (a.k.a. glory-of-the-snow). They really don’t look that much alike, except they are both small, ephemeral, blue flowered, perennial bulbs. The most obvious different, though, is that Scilla (or squill, not to be confused with Scylla) has downward facing flowers while Chionodoxa has mostly upward facing flowers. There are other more subtle differences. Seeing them side by side, you might wonder how anyone would mistake one for the other. In any case, I have them pretty well separated in my mind now.
Of course, deciding which of them I prefer is not so easy. They are both beautiful in their own way. I don’t suppose I have any great need to pick one over the other. I think both should be planted far more often than they are. They grow well, they are quite hardy, and they are beautiful. Do you need more than that? Well, if you do, how about the fact that Scilla siberica has blue pollen?