This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Handsome shrubs bearing large showy pink, rose, or white flowers in axillary and terminal clusters. Calyx-tube very slender, produced above the ovary. Corolla funnel - shaped or campanulate, nearly regular. Stamens 5. Style single, slender, exserted; stigma capitate. Seed-vessel long and narrow, coriaceous or membranous, many-seeded. The species are natives of Eastern Asia and North America. Named after a botanical author.
l. D. rosea, syn. Weigela rosea (fig. 117). - A highly ornamental species, and the first of this group introduced. It is of small stature, with ovate-lanceolate serrulate leaves and a profusion of rosy or white flowers in April or May. It is a native of China. There is a variegated and other garden varieties. D. fiorida is probably a form of this. D. Japonica is hardly different from D. rosea.
2. D. amabilis, syn. Weigela amabilis. - Very near the last, though of rather larger stature and foliage. The principal difference is in the leaves, which are strongly reticulated, the veins being very prominent on the under side. There are many handsome varieties of this and the foregoing, some of which are probably of hybrid origin. Isolince has white flowers with a yellow blotch in the throat; striata, striped red and white; Van Houttei, white and rose, very showy; Stelzneri, purplish red, very floriferous. The two latter are usually-referred to D. rosea.
Fig. 117. Diervilla rosea. (1/6 nat. size.)
D. Middendorftana has nearly sessile ovate-lanceolate finely reticulated leaves hairy on the nerves, and yellowish white flowers dotted with pink on the lower petal. The latter are arranged in terminal panicles, and are peculiar in having the anthers combined. A native of Siberia. D. purpurata is considered to be a variety of this species.
D. multifiora, syn. floribunda. - A Japanese species, very distinct in its narrow tubular purplish corollas only slightly expanded towards the mouth. D. Canadensis is an allied species with yellow flowers.