Phlomis grandiflora, like the more commonly-seen Phlomis fruticosa is often given the name of Jerusalem Sage and superficially is very similar to Phlomis fruticosa. Both large, woody-stemmed and yellow-flowering they are not always easy to tell apart especially when young. Phlomis grandiflora grows larger the Phlomis fruticosa and can reach a staggering 3m tall although 2m is more usual. When young, the best way to tell them apart is by their leaves. The foliage of Phlomis grandiflora is green and hairy above while the foliage of Phlomis fruticosa is greyish and tomentose on the upper surface. With age the foliage turns silvery. The leaves on Phlomis grandiflora are longer than those of P. fruticosa but have a shorter petiole. When flowering, the verticillasters (the wonderful spherical whorl-like inflorescence) of Phlomis grandiflora are one-headed whereas on P. fruticosa the stems often have more than one verticillaster.

In the wild, the two populations often overlap, particularly in Turkey - their generic epicentre - but the Phlomis grandiflora population is found more to the east while Phlomis fruticosa is found more to the west as far as Italy and Sardinia.

Like all Phlomis, Phlomis grandiflora thrives in full sun and a well-drained alkaline soil.