Nauclea Korthals, Observ. Naucl. Indic. 17. 1839, not Linnaeus (1762).

Trees or shrubs, unarmed; buds flattened with stipules erect and pressed together [to conical], [sometimes with fusiform swellings housing ants in branches]. Raphides absent. Leaves opposite, sometimes with numerous foveolate domatia; stipules caducous [or rarely persistent], interpetiolar, generally ligulate, entire. Inflorescences terminal, capitate with 1-9 globose heads in fascicles or cymes, many flowered, pedunculate, bracteate; peduncles and axes articulate near middle; bracts enclosing heads involucrate and caducous; bracteoles spatulate to conical or sometimes absent. Flowers sessile, bisexual, monomorphic. Calyx limb deeply 5-lobed; lobes prolonged into a slender shaft bearing thickened to rhomboidal apical portion, this often ornamented and/or pubescent differently from shaft and frequently deciduous before shaft. Corolla pale green to white or red, salverform to narrowly funnelform, inside glabrous or glabrescent; lobes 5[or rarely 6], imbricate in bud. Stamens 5, inserted in corolla throat, partially to fully exserted; filaments short; anthers basifixed. Ovary 2-celled, ovules numerous in each cell, pendulous on axile placentas attached in upper third of septum; stigma globose to obovoid, exserted. Fruiting heads globose. Fruit capsular, obconic, septicidally then loculicidally dehiscent into 4 valves from base to apex, with valves separating from septum, with septum persistent on inflorescence or later deciduous, woody to cartilaginous, with calyx limb deciduous with capsule valves; seeds numerous, small, fusiform, flattened, winged; embryo ellipsoid, somewhat bilaterally compressed.

This genus was studied in some detail by Ridsdale (Blumea 24: 337-342. 1979; Blumea 34: 177-275. 1989). The unusual, usually quite elaborately developed calyx lobes are distinctive of the genus in general, and their form is distinctive for individual species; care must be taken to look for the caducous apical part of the calyx lobes and to not confuse the persistent tubular calyx limb base with the entire calyx limb. Ridsdale (loc. cit. 1989) developed a very detailed terminology, but did not suggest a function, for the calyx lobe morphology of this genus. He also noted that Neonauclea has secondary pollen presentation. Ridsdale (loc. cit. 1989) and Zou (J. Arnold Arbor. 69: 73-76. 1988) noted that some Neonauclea species are large trees that produce very good lumber.

About 62 species: tropical Asia and Pacific islands, perhaps ten species in continental Asia; four species (one endemic) in China.

(Authors: Chen Tao (陈涛); Charlotte M. Taylor)