1. Toona (Endlicher) M. Roemer, Fam. Nat. Syn. Monogr. 1: 131. 1846.
香椿属 xiang chun shu
Authors: Hua Peng & Jennifer M. Edmonds
Cedrela sect. Toona Endlicher, Gen. Pl. 2: 1055. 1840; Surenus Rumphius ex Kuntze, nom. illeg. superfl. (included type of Toona).
Trees to 50 m tall, monoecious, deciduous or semideciduous. Bark grayish brown, fissured, sometimes flaking irregularly; inner bark pink to red; sapwood cream-colored. Leaves spirally arranged, even-pinnate or occasionally odd-pinnate; leaflets usually more than 8 on each side of rachis; leaflet blades glabrous or pubescent with simple trichomes but with club-shaped glands often associated with veins, margin entire, serrate, or dentate; domatia (small deltate axillary pockets) usually present on proximal lateral veins of abaxial surface, often bordered with simple trichomes. Inflorescences much-branched pendent thyrses, often exceeding 1 m. Flowers 5-merous, unisexual with well-developed vestiges of opposite sex present, rarely hermaphrodite, small. Calyx 5(or 6)-lobed or 5(or 6) distinct sepals; sepals imbricate or cup-shaped in bud, margins always ciliate. Petals 5(or 6), white, cream-colored, or pink, distinct, longer than calyx in bud, imbricate (quincuncial), basally adnate to a short pulvinate androgynophore (disk). Stamens 5(or 6), distinct, arising from androgynophore, sometimes alternating with 1-5 filamentous staminodes; anthers in male flowers yellow, dehiscing laterally; antherodes in female flowers often sagittate, brown with abortive pollen. Ovary 5-locular, with 6-10 ovules per locule, vestigial in male flowers; style short in female flowers, pistillodes long and slender in male flowers; stylehead discoid with stigmatic papillae, usually 5-rayed. Fruit a capsule, ellipsoid or obovoid, pendulous, thinly woody, septifragal; valves 5, brown, smooth to verrucose, opening from apex; columella softly woody, concavely or convexly 5-angled, extending to capsule apex. Seeds numerous per locule, winged either at both ends when attached toward distal end of columella or at one end when attached by seed-end to proximal part of columella; wings membranous; endosperm residual; cotyledons collateral, flattened, leaflike; radicle laterally exserted.
About five species: E, S, and SE Asia, E Australia; four species (one endemic) in China.
This treatment of Toona largely follows J. M. Edmonds treatment (Fl. Males., Ser. 1, Spermat. 12(1): 358-371. 1995), in which a more complete synonymy can be found.
The timbers of Toona species are highly prized but now generally scarce through excessive logging activities throughout their distributional ranges. The genus is composed of only a few species, but phenotypic plasticity and genetic variation are responsible for much of the taxonomic complexity reflected in the literature. The species exhibit a phenomenal range of morphological variation, both within and between trees of the same population, and many of the features used by earlier authors to define their taxa have proved to be only slight morphological variants. Such vegetative characters include leaf and leaflet size; leaf and leaflet margin shape; indumentum type and trichome density. In particular, the velutinous pubescence, on which a number of Toona taxa have been based, occurs throughout the genus with the exception of T. sinensis, both inter- and infraspecifically, and even between seedlings of the same population. Both flowers and fruits are necessary for accurate identification of Toona species. This is especially relevant to T. sureni and T. ciliata, which are particularly difficult to differentiate in the herbarium.