Possibly Decaisne's Pyrus bollwilleriana, first described by Lindley in 1437. Decaisne (1858, translated from French by M. Westwood in 1996) wrote The pear of Pollwiller is a remarkable example of the persistence of the characters of a hybrid tree, propagated for three centuries by grafting, and which contradicts everything said on the subject of the disappearance and the degeneration of our ancient varieties of fruit trees. In 1860 Decaisne collected 450 fruits, found only 13 well formed seeds - seedlings varied from pear-like to sorbus-like. Decaisne quoted from Chabraeus, 1666: This is the most rare and beautiful genus of pear, up to the present, and we have never seen it except in Pollvillam in Alsatia and the garden of th Prince Montbelgardi. Possibly the genus is the alpine Sorbus?
Decaisne quoted from J. Bauhin, 1619: The pollwiller pear is considered the rarest and most beautiful genus of pear by the noble Barons of Pollwiller; they call it Rotbirle.