I should have known, of course. In a recent post on trees and pollen, I wrote:
Bee-pollinated trees don’t bother to release the kind of pollen that makes you sneeze, and wind-pollinated plants don’t bother to attract bees. (There may be belt-and-suspenders plants out there that can be pollinated by wind but would like also to be pollinated by bees, but this non-botanist isn’t aware of them. Readers?)
I like taxonomy and either/or, but nature likes redundancy and both/and. Nature is right; I stand corrected.
Species with a Plan B tend to stick around longer. So it turns out at least two genera of New England trees (and probably many more elsewhere) are both wind- and insect-pollinated. Maples and Willows have small but clearly visible flowers that are pollinated both by wind and by insects.

Our native Columbine, Aquilegia canadensis, has a back-up plan too. Its long red nectaries attract hummingbirds and its yellow bits attract bugs.
Thank you to Frances Clark, in her excellent Wildflowers of New England class at Garden In the Woods, for cluing me in on this.
There are other bird-pollinated plants, and – for the smaller ones – plants pollinated by animals brushing by; even humans may inadvertently pollinate some.