The correct authorities, as per IPNI and POWO are:
Rudbeckia grandiflora (Sweet) C.C.Gmelin ex de Candolle var. grandiflora, as listed in the species name, but the variety authorities are given in VASCAN as (D.Don) J.F. Gmelin ex de Candolle var. grandiflora
See: https://www.ipni.org/?q=Rudbeckia%20subtomentosa
The correct authorities, as per IPNI and POWO are: Rudbeckia grandiflora (Sweet) C.C.Gmelin ex de Candolle var. grandiflora, as listed in the species name, but the variety authorities are given in VASCAN as (D.Don) J.F. Gmelin ex de Candolle var. grandiflora