Description from Flora of China
Capura Linnaeus; Diplomorpha Meisner.
Shrubs or subshrubs, occasionally small trees or rarely a herbaceous perennial (W. linoides), evergreen or deciduous. Leaves opposite or alternate. Inflorescence usually terminal and subterminal, rarely axillary, fascicled or solitary, spicate, racemose, umbelliform or capitate, sometimes in compound terminal panicles, often without involucre; peduncle long or short. Flowers bisexual or unisexual (Hawaii), 4- or 5-merous, subsessile or distinctly pedicellate; pedicel articulate. Calyx tube yellow or green, less often purplish, red or white, cylindric or tubular, sometimes slightly funnel-shaped, often caducous after anthesis, sometimes persistent; lobes 4 or 5, spreading. Petaloid appendages absent. Stamens twice as many as calyx lobes, in two series; filaments very short; anthers oblong, upper sometimes slightly exserted; connectives indistinct. Disk with 2 or 4, very rarely 1 or 5, scales, rarely joined at base by very narrow annulus, membranous. Ovary sessile, rarely shortly stipitate, usually ellipsoid, glabrous or hairy at apex, 1-loculed; style terminal, short, distinct or obscure; stigma large, capitate, globose, or discoid. Fruit a succulent berry or rather dry. Endosperm scanty or absent; cotyledons fleshy.
The separation of Wikstroemia from the following genus, Daphne, is problematic. Features such as leaf arrangement, inflorescence type, and flower color are all clearly paralleled within the two genera and are of no diagnostic value, although they are mentioned in most keys to these genera. In most cases, the nature of the hypogynal disk is diagnostic, but even here there are species where the interpretation of the structure of the disk is difficult. For example, the distinction between the lateral ± square disk seen in several species of Daphne and species of Wikstroemia with a single large disk scale, or species of Wikstroemia in which the disk scales are connected by a narrow annulus, or species of Daphne with very deeply divided disks makes the division seem rather arbitrary, such that there must be a good case for combining these two genera, as was done by Halda (Genus Daphne. 2001). A review of generic delimitations in the family based on molecular data would be very desirable.
Wikstroemia ganpi (Siebold & Zuccarini) Maximowicz was indicated by Halda (loc. cit.: 158, as Daphne ganpi (Siebold & Zuccarini) Halda) to occur in Taiwan, but this species has not been recorded by botanists from Taiwan, and the basis of the record was not indicated.
Wikstroemia bodinieri H. Léveillé is a synonym of Alyxia schlechteri H. Léveillé in the Apocynaceae (see Fl. China 16: 162. 1995). Wikstroemia hemsleyana H. Léveillé is a synonym of Alstonia mairei H. Léveillé also in the Apocynaceae (loc. cit.: 156).
About 70 species: E Asia, Malaysia, Australia, and Pacific islands with a significant minor center of diversity in Hawaii where many species are dioecious; 49 species (43 endemic) in China.
(Authors: Wang Yinzheng (王印政); Michael G. Gilbert)