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A genus composed mainly of herbaceous perennials, but including the four woody species treated here. These constitute the section Moutan, which is confined to W. China and S.E. Tibet.
The genus Paeonia, long included in the family Ranunculaceae, is now placed in a separate family, of which it is the only genus. Leaves alternate, deeply divided. Flowers large and showy; sepals five, persistent; petals normally five, sometimes ten (and often very numerous in garden varieties); stamens very numerous, the anthers dehiscing centrifugally, i.e., the innermost shedding their pollen first (in the Ranunculaceae it is the other way about); carpels fleshy, up to five in number, free from one another, each developing into a follicle containing a few large arillate seeds. In Paeonia (but not in the Ranunculaceae) a disk is present at the centre of the flower. In P. suffruticosa this is very developed, forming an envelope round the carpels, while in other species of the section Moutan it forms a lobed, fleshy structure at the base of the carpels.
For the propagation of the garden varieties and hybrids see p. 83. Division is the best means of increasing P. potaninii, while P. lutea and its variety, and P. delavayi are usually propagated by seeds. If these are sown as soon as they are ripe in early autumn, there is a good chance that they will germinate the following spring, without artificial heat or any special treatment. The seed is otherwise best kept cool and dry, and sown in the spring or early summer; it will then germinate in the spring following. The explanation for this procedure is that root-germination takes place in warmth, but the embryonic shoot remains dormant until the seed has undergone a period of low temperature, which is only effective after the period of warmth.
The standard work on the taxonomy of the paeonies is: F. C. Stern, A Study of the Genus Paeonia (1946). Other useful works are: M. Haworth-Booth, The Moutan or Tree Paeony (1963); J. C. Wister, ‘The Moutan Tree Peony’, in Peonies: The Manual of the American Peony Society (1928); J. C. Wister and H. E. Wolfe, ‘The Tree Peonies’, in Nat. Hort. Mag. (1955), Vol. 34, pp. 1-61.