Gleditsia

Authority

Isley, Duane. 1975. Leguminosae of the United States: II. Subfamily Caesalpinioideae. Mem. New York Bot. Gard. 25 (2): 1-228.

Family

Caesalpiniaceae

Scientific Name

Gleditsia

Description

Genus Description - Trees, usually with branched thorns. Leaves of two kinds in most species, 2-pinnate and alternate on new growth, and 1-pinnate from spurs, some introduced Old World species with mostly 1-pinnate, alternate leaves. Stipules obsolescent. Plants polygamous, bearing reduced flowers in two kinds of inflorescences appearing with leaves from spurs (otherwise in some Asiatic species). Staminate inflorescences catkin-like, racemose or somewhat branched with clustered, subsessile to briefly pediceled flowers; fertile inflorescences with perfect or pistillate, ascending, usually spaced, strongly pedicelled flowers; hypanthium short-campanulate; perianth regular, pubescent, of two similar yellowish-green series; sepals 3-5; petals 3-5, broader and slightly longer than sepals; stamens mostly 6-8, the filaments with fine hairs at base. Legume indehiscent, stipitate, oblong and large, compressed to subterete, pulpy and many-seeded, brittle-coriaceous to subligneous at maturity; or short, flat, ovate, dry, one-few-seeded.

Discussion

CBN x = 14. Gleditsia is most amply represented in temperate Asia. Atchison (1949) and Gordon (1966) present a classic thesis that Gleditsia is an ancient genus characterized by wide distribution and great age; this position being documented by fossils which date back to the Upper Cretaceous. Atchison believes that similarity in chromosome number of several widely disjunct species further supports this proposition but her vouchers (foliage only) for G. horrida, G. amorphoides, and G. sinensis all appear to be G. triacanthos. That lack of nodulation is another indication of antiquity (e.g. Gordon, 1966), is dubious inasmuch as nodulation is infrequent in the Caesalpinioideae as a whole. McDougall (1921) described specialized thick-walled root-hairs characteristic of Gleditsia triacanthos and to a lesser extent of Gymnocladus and Cercis. Because root hairs of this general type are “commonly associated with xerophytic conditions” this author suggested that the roots and the thorns of Gleditsia are relics of a time when species possessing them grew under xerophytic conditions. I am doubtful that xeric or desert progenitors of these genera are likely. The thorns of Gleditsia were investigated by Blaser (1956) who found them to represent a reduced, determinate branch system.

Distribution

Primarily of Asia and North America but of all continental land masses except Australia, 14 species. Ours, 2 native to e and c U.S. and 1 widely cult., others introduced.

Asia| North America| South America| Europe| Central America| Africa|