Lesser whitebeam grows at a few sites in the traditional county of Breconshire, a part of modern Powys.

It grows on Carboniferous Limestone cliffs near Crickhowell on the northern edge of Mynydd Llangatwg in the Brecon Beacons National Park.

Smaller numbers grow further west at Cwm Cleisfer and a single plant remains at Craig y Castell.

By raising the issue in the House of Commons, and inducing War Secretary Frederick Bellenger to order the Army to pull out of the area, Tudor Watkins, Labour MP for Brecon and Radnorshire is credited with preserving the species from extinction.

All the locations where the species grows, apart from Cwm Cleisfer, now have some kind of protection and a population is kept at the National Botanic Garden of Wales.