If you mean an acrostic, you could have: WallflowerIris
Nasturtium
Tulip
Echinops
Rudbekia.
If you mean flowers associated with winter, you could have helleboris niger (Christmas rose), winter jasmine and snowdrop.
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Generally, any number of flowers can be appropriate for winter,
especially depending upon location. Some traditional winter wedding
flowers include Lily of the Valley, Amaryllis, Poinsettia, and
evergreens.