Gymnocladus Lam. Encycl. Meth., Bot. 1: 733. 1785.

Figs 13, 14, 16

Lectotype.

Gymnocladus canadensis Lam., nom. illeg. [= Gymnocladus dioicus (L.) Koch (≡ Guilandina dioica L.; vide Britton and Rose 1930)]

Description.

Large to medium size deciduous trees, unarmed, stems often stout, androdioecious (individuals with either staminate flowers or hermaphrodite flowers) or dioecious. Stipules small, inconspicuous. Leaves even- or irregularly-bipinnate, pinnae 3-10 pairs, proximal-most sometimes reduced to single leaflets, opposite, subopposite or alternate; leaflets alternate, 6-30 per pinna, lamina margin entire (Figs 13D, 14F, G). Inflorescences terminal, racemes or panicles, 15-50 flowers (Fig. 14E, F); bracts and bracteoles usually absent, sometimes present, minute. Flowers white, greenish white, or purple, pedicellate, regular, hypanthium elongate; calyx lobes 5, narrow; corolla lobes 5, wider than sepal lobes; stamens 10, inserted on hypanthium; pollen exine perforate to reticulate; ovary sessile or short-stipitate, style short, thick (Fig. 14C, D). Fruit sessile, compressed, turgid, oblong, indehiscent or tardily dehiscent on placental suture, woody, pulpy between seeds, 1-8-seeded (Fig. 13H). Seeds subglobose to somewhat flattened, testa smooth to rough.

Chromosome number.

2 n = 28 (Goldblatt 1981b).

Included species and geographic distribution.

Six species in eastern and central North America, China, Vietnam, India, Burma, Thailand (Fig. 16). The limits of the natural distribution of G. dioicus are unclear due to its widespread cultivation in eastern North America. Gymnocladus assamicus Kanjilal ex P.C. Kanjilal from the eastern Himalayan region of India is critically endangered.

Ecology.

Temperate bottomlands and riparian woodlands, tropical and subtropical montane woodlands and wooded hillsides (Chen et al. 2010c).

Etymology.

The genus name derives from the Greek (= naked branch) because G. dioicus is one of the latest trees to leaf out in the spring.

Human uses.

Multiple species of Gymnocladus are used by people in different parts of the world (Lee 1976; Allen and Allen 1981; Poindexter et al. 2022a). Gymnocladus dioicus is widely planted as an ornamental and street tree. The wood of G. dioicus and G. chinensis is used for fence posts, construction, railway ties and carpentry. Roasted seeds of G. dioicus were formerly used as a coffee substitute, hence the common name Kentucky Coffee Tree used in North America. Some species are used for medicine, insecticides, oils, and soap.

Notes.

The taxonomy of the species of Gymnocladus is well established, but the monophyly of the genus has not been adequately tested. Only G. dioicus and/or G. chinensis have been included in phylogenetic analyses (Herendeen et al. 2003b; Schnabel et al. 2003; Choudhury and Khan 2020; Feng et al. 2021; Ringelberg et al. 2022). Given the morphological variation among the species of Gymnocladus and similarities to Gleditsia it would be worthwhile to test the monophyly of Gymnocladus in an analysis that includes more species and samples. Lee (1976) recognised four species in the genus (two additional species were described subsequently), which he hypothesised to be of tropical origin. Choudhury et al. (2014) documented functional androdioecy in G. assamicus . The chloroplast genome of G. chinensis was characterised by Feng et al. (2021).

Taxonomic references.

Allen and Allen (1981); Poindexter et al. (2022a); Schnabel et al. (2003).