Jalas (HBraun) 1971 - Heywood VH (1971) Flora Europaea: Notulae Systematicae ad Floram Europaeam spectantes: No. 10. Botanical Journal of the Linnean Society 64(3): 247-275. doi: 10.1111/j.1095-8339.1971.tb02147.x.
There is no corrections for Thymus praecox subsp. zygiformis yet.