Allow me to plagiarise the AIPC magazine special on Mexican Pings (Special issue 3) which I find is an excellent resource to looking something up. I've added some more reader friendly descriptions in brackets.
Description: The summer rosette is up to 5 cm broad and is composed of semi-succulent, obovate(egg shaped)-spathulate(shaped like a small spatula) leaves, densely overlapping and light green to reddish in colour. The leaf margin, involute(leaf margin rolled inwards) at the apex, is peculiar in that it is also much paler than the upper surface of the leaf. The winter rosette is pulvinate. The flower is quite large, usually about 2 cm wide with cuneiform(wedge shaped) lobes coloured from pale pink to lilac. It is paler at the throat and shows a pubescent, yellowish spot on the lower median lobe. Flowering occurs in the period of vegetative resumption.
Description: The compact summer rosette, composed of overlapping semi-succulent leaves, can reach 5 cm in diameter and is very similar to those of P. esseriana and P. ehlersiae, as is the winter rosette. The corolla is lilac in colour with cuneate-obovate shaped lobes that are 0.8 to 1.2 cm long, with a yellow to brown spot on the median lower lobe. The throat is paler with a faint veining and pubescent. Flowering occurs at the end of winter dormancy.
It seems the difference really is very small. I know of my plants in the current winter rosette there is no discernible difference between Jaumavensis, Esseriana and Ehlersiae.