Black locust reaches a typical height of 12–30 metres (40–100 feet) with a diameter of 0.61–1.22 m (2–4 ft).[6] It is a very upright tree with a straight trunk and narrow crown that grows scraggly with age.[7] The dark blue-green compound leaves with a contrasting lighter underside give this tree a beautiful appearance in the wind and contribute to its grace.
Black locust is a shade-intolerant species[8] and therefore is typical of young woodlands and disturbed areas where sunlight is plentiful and the soil is dry. In this sense, black locust can be considered a weed tree. It also spreads by underground shoots or suckers, which contributes to the weedy character of this species.[7] Young trees are often spiny, but mature trees often lack spines. In the early summer black locust flowers; the flowers are large and appear in large, intensely fragrant clusters reminiscent of orange blossoms. The leaflets fold together in wet weather and at night (nyctinasty), as some change of position at night is a habit of the entire leguminous family.
Although similar in general appearance to the honey locust, the black locust lacks that tree’s characteristic long branched thorns on the trunk, having instead pairs of short prickles at the base of each leaf; the leaflets are also much broader than honey locust. It may resemble Styphnolobium japonicum, which has smaller flower spikes and lacks spines.
