The Quince Cydonia oblonga, the sole member of the genus Cydonia, is a small to medium size tree native to warm-temperate southwest Asia in the Caucasus region.uince foliage and fruit. Quinces are too hard, astringent and sour to eat raw unless 'bletted' (softened by frost). They are used to make jam, jelly and quince pudding, or they may be peeled, then roasted. The very strong perfume means they can be added in small quantities to apple pies and jam to enhance the flavour.