Peony
2 of the 7 encyclopedias on this shelf carry an entry for Peony. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
Important: Safety Warning This page prescribes plants as medicine according to pre-modern medical theory. Several of the plants named are toxic, correct identification is difficult, and the doses given have no scientific basis. Do not ingest or apply any preparation described here. This information has been left in for historical purposes but should not be acted upon. a genus of plants belonging to the natural order Ranunculaceæ, and very generally cultivated in gardens for the sake of their large showy flowers. The species are mostly herbaceous, having perennial tuberous roots and large deeply-lobed leaves. The flowers are solitary, and of a variety of colors, crimson, purplish, pink, yellow, and white. The flowers, however, have no smell, or not an agreeable one, except in the case of a shrubby species, P. Moutan, a native of China, of which several varieties, with beautiful whitish flowers stained with pink, are cultivated in gardens. The roots and seeds of all the species are emetic and cathartic in moderate doses. P. officinalis or festiva, the common peony of cottage gardens, was formerly in great repute as a medicine.
Aiton's Encyclopedia (1910)
a family of showy perennials familiar in gardens. Known also as paeony and "piney." The name is from the Greek Paean, the physician of the gods, having reference to the reputed medicinal properties of the root. The peony is a member of the buttercup family. There are numerous European and Asiatic species. There is also a species native to the Pacific coast of North America . The peony may be propagated either from seeds or from root-stocks. The old-fashioned red peony has been known ever since the day of the Roman Pliny. The peony is particularly free from the attacks of insects. A clump well established and sheltered by mulch in the winter produces an abundance of flowers for many years. The florist has succeeded in producing double peonies. Two or three dozen varieties are now in cultivation. One species raised in China is a stout shrub with large rose-colored or white flowers.