Hartwig Locust Tree – Robinia hartwigii

Hartwig Locust Tree – Robinia hartwigii
Family: Fabaceae (Leguminosae)

USDA Hardiness Zone: 3. Live specimens photographed at The Morton Arboretum

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Hartwig Locust Tree

Leaf: alternate, pinnately or bipinnately compound with 14 to 20 oval to elliptical leaflets each 3/4 to 1 inch long, overall leaf 6 to 8 inches long.
Flower: Greenish white flowers displayed in 2 inch long racemes, appearing after the leaves.
Fruit: Flat, brown, almost round pods, 1 to 2 inches long, each containing 1 to 3 seeds.
Twig: Slender to moderate, zigzag, grayish to red-brown, conspicuous thorns, lateral buds sunken.
Bark: Smooth, grayish brown, often mottled, lenticels present, later splitting.
Form: Small to medium sized tree to 50 feet with a spreading, open crown.

The Fabaceae are herbs, vines, shrubs, trees, and lianas found in both temperate and tropical areas. They comprise one of the largest families of flowering plants, numbering 630 genera and 18,000 species. The leaves are stipulate, nearly always alternate, and range from bipinnately or palmately compound to simple. The petiole base is commonly enlarged into a pulvinus that commonly functions in orientation of the leaves (sometimes very responsively, as in the sensitive plant, Mimosa pudica). The flowers are usually bisexual, actinomorphic to zygomorphic, slightly to strongly perigynous, and commonly in racemes, spikes, or heads. The perianth commonly consists of a calyx and corolla of 5 segments each. The androecium consists of commonly 1- many stamens (most commonly 10), distinct or variously united, sometimes some of them reduced to staminodes. The pistil is simple, often stipitate, comprising a single style and stigma, and a superior ovary with one locule containing 2-many marginal ovules. The fruit is usually a legume, sometimes a samara, loment, follicle, indehiscent pod, achene, drupe, or berry. The seeds often have a hard coat with hourglass-shaped cells, and sometimes bear a u-shaped line called a pleurogram.

The native thorny locust species is found on both sides of the Mississippi River from Nebraska to Texas and from Pennsylvania to Alabama. Fence rows and pastures are common locations.

1. Colorado State University, "Sunburst Honeylocust (Gleditsia triacanthos ‘Sunburst’)"
2. Sunburst Honey Locust, Morton Arboretum acc. 366-56*1, photos by Bruce Marlin

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Family: Fabaceae (Leguminosae)
The Fabaceae, or legumes, are mostly herbs but include also shrubs and trees found in both temperate and tropical areas. They comprise one of the largest families of flowering plants, numbering some 400 genera and 10,000 species. Peanuts, beans, peas, wisteria and locust trees are among the family.
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