2. Gleditsia triacanthos L. (honey locust)

Map 1693, Pl. 386 g–i

Plants trees 20–30 m tall or taller, usually armed with conspicuous thorns, these 2–7 cm long, 2–4 mm in diameter at the base, simple or often several-branched, the bark smooth and reddish brown on young trunks and branches, becoming deeply fissured and dark gray to nearly black on older trunks. Leaves with the petiole and rachis distinctly short-hairy, the 1 time compound leaves 12–14 cm long, with 7–16 pairs of leaflets, these 1–4 cm long, 7–14 mm wide, narrowly ovate, rounded at the tip, the upper surface glabrous and green to dark green, the undersurface short-hairy and pale; the 2 times compound leaves with 3–6(–8) pinnae, each with (2–)5–10 pairs of leaflets, these 1.3–2.5 cm long, 7–12 mm wide, narrowly ovate to ovate, rounded at the tip, the upper surface glabrous and green to dark green, the undersurface short-hairy and pale. Inflorescences spikelike racemes 5–10 cm long, with many fragrant flowers, the pistillate inflorescence with fewer and more widely spaced flowers than the relatively dense staminate ones. Flower stalks 0.5–3.0 mm long. Sepals 2–3 mm long, 1.0–1.4 mm wide, finely hairy. Petals 2.0–2.2 mm long, 1.4–1.8 mm wide. Fruits with the stalklike base 1–3 cm long, the body 18–35 cm long, 2.5–3.0 cm wide, elongate, flattened, curved or spirally twisted, the surfaces glabrous or hairy, purplish brown, the seeds embedded in a jellylike pulp, this eventually becoming dry and inconspicuous. Seeds 8–10 mm long, 6–7 mm wide, ovoid, olive green to brown. 2n=28. May–June.

Scattered to common nearly throughout the state (nearly throughout the U.S.; Canada; introduced in Australia). Bottomland forests, mesic upland forests, banks of streams and rivers, margins of sinkhole ponds, edges of glades, and edges of and drainages in upland prairies; also pastures, old fields, fencerows, and roadsides.

Honey locust is a very useful plant. It is very tolerant of urban and suburban conditions and makes an excellent shade tree, especially the thornless selections. The wood is hard and durable and is used for a variety of wood products, including fence posts and furniture. The legume pods are an important food for wildlife, and trees sometimes are planted in pastures for livestock. The pods have a sugar content of 13–30 percent, and the seeds have a protein content of 16–28 percent (Gold and Hanover, 1993). The pods can be gathered and ground to provide food for livestock with a nutritional value about that of alfalfa. Experimental plantings have produced over 6 tons of dry fruits per acre. Steyermark (1963) enjoyed the sweet pulp surrounding the seeds as a treat while hiking. The tree is fast-growing and very drought tolerant and is planted for windbreaks and erosion control. Unfortunately, although honey locust probably was mostly a bottomland tree originally, it is invasive in a variety of upland habitats, especially prairies in northern Missouri. It also tends to proliferate in disturbed bottomland forests.

The thorns of G. triacanthos represent a reduced branch system. They have been used in handicrafts, as large needles, as weapons, and for carding wool. The most commonly planted trees are thornless forms, which are found sporadically in nature throughout the range of the species; these have been called f. inermis Zabel. Cuttings taken from the upper, thornless, portions of otherwise thorny trees will also produce thornless individuals. However, the thornless condition appears to be genetically unstable. Offspring of thornless individuals sometimes produce thorns, and Michener (1986) has reported mature thornless specimens reverting to a thorny state.

The large spines and big fruits of G. triacanthos may be adaptations for large Pleistocene mammals such as horses, giant sloths, mastodons, and mammoths (Janzen and Martin, 1982; Barlow, 2000). These creatures were present in North America for millions of years and only became extinct in the last 10,000–20,000 years, perhaps at the hand of man. The spines may have protected the trees from these large animals. The pods of G. triacanthos have all the characteristic features of the so-called megafaunal dispersal syndrome discussed by Janzen and Martin (1981): they are large, more or less indehiscent, contain a nutritious pulp, and have hard seeds that would survive mastication. Passage of the seeds through the gut of large animals would serve to scarify them and speed germination. Present-day mammals such as horses and cattle eat them readily. No other large native mammals exist to disperse the seeds at present, which may be a factor in the often spotty distribution of the species. Other plants in the Missouri flora that similarly may have lost their original seed dispersers include Kentucky coffee tree (Gymnocladus dioica, Fabaceae), Osage orange (Maclura pomifera, Moraceae), pawpaw (Asimina triloba, Annonaceae), and persimmon (Diospyros virginica; Ebenaceae).