Abstract
Present distr. of the genus Paeonia was studied from both the geographical and the cytological approach and inferences were made concerning the migration of various spp. both during the advance of continental glaciers and the subsequent plant re-occupation of the glacially devastated areas. The tetraploid member of a morphologically closely allied Paeonia spp. group almost always occupies at present a wider and less restricted range in Europe than does the diploid member. One diploid sp. P. cambessedessii is confined to the Balearic Is., while the allied tetraploid P. russi and its vars. extend over Corsica, Sardinia, and Sicily. The diploid P. clusii is restricted to Crete and nearby Karpathos, and the allied tetraploids P. officinalis and related spp. occur along the Dalmatian coast from Albania into n. Italy and Switzerland, then into s. France and central Spain. Rhodes is the present range of diploid P. rhodia. while the related tetraploid P. arietina and its vars. range from Armenia westward across Asia Minor to Bosnia and southward into Syria, Cyprus, and Crete. Diploid P. daurica grows only in or near the Crimea but allied tetraploids P. mascula and P. banatica spread westward across Europe to central France. Two tetraploids. P. peregrina, indigenous only to the Balkans, and P. coriacea. occurring only in s. Spain, Morocco and Algiers, have no allied diploid spp.; presumably the original diploid spp. have died out. In Japan one diploid P. japonica is matched on the Chinese mainland by the allied tetraploid P. obovata. All other Paeonia spp. in e. Asia are diploids with characters uncommon in the genus, such as more than one flower to a stem, as in P. lacifolia, P. veitchii and P. emodi, and shrubbiness as in the tree peonies which occur only in this region. It is inferred that these 2 characters suggest primitiveness. Two closely connected spp. P. brownii and P. californica in western U. S. A. are diploid herbaceous spp. and are closely related in botanical characters to the shrubby spp. of w. China. The oldest Paeonia spp. in Europe are diploid and are found only in Portugal, the islands of the Mediterranean, the Crimea and Volga region, and a small area in the Caucasus; they are probably pre-glacial relicts. Tetraploid spp. arising from these relicts are abler competitors with other flora under post-glacial conditions and are stronger under cultivation than the original diploids. On the other hand diploid Paeonia spp. in the Lake Baikal and Volga districts outside the glacial limits in Europe could spread again directly into the ice-devastated area against little competition. Diploid spp. in western U. S. A., Manchuria and China where continental ice did not invade, are probably ancient pre-glacial relicts.