The most striking aspect of this shrub consists of the bristly purple-brown hairs that cover young stems, pedicels, calyces, and seedpods. These hairs probably discourage herbivory by some insects and deter nectar-robbing of the flowers by ants. Another species in this genus with a similar appearance is Robinia viscosa (Clammy Locust). While stems, calyces, seedpods, etc. of this shrub are covered by short sticky glands, they lack the long purple-brown hairs of Bristly Locust. Another species, Robinia pseudoacacia (Black Locust), is a tree that has spread northward into all areas of Illinois. This tree also lacks the long purple-brown hairs of Bristly Locust and its flowers are white, rather than rosy pink. In its native range in southeastern United States, Bristly Locust is a rather variable shrub and different varieties have been described. The typical variety (var. hispida) has been described here because it is more often encountered than other varieties of this shrub.

This introduced shrub is 3-10' tall and across, branching abundantly. The bark of the trunk and larger branches is gray and fairly smooth. Young branches are green, terete, and very bristly-hairy. These long bristly hairs are purple-brown and sticky from minute glands. Alternate compound leaves occur at intervals along young branches; they are ¾–1½' long and odd-pinnate with 7-15 leaflets. The green rachis (central stalk) of each odd-pinnate leaf is slightly sticky-hairy. At the base of each rachis is a pair of sharp spines. Individual leaflets are 1-2" long and one-half as much across; they are broadly oblong, smooth along their margins, and hairless (or nearly so). Their upper surfaces are medium green, while their lower surfaces are pale green. Both axillary and terminal racemes of flowers are produced. Each raceme has 5-15 rosy-pink flowers; both the central peduncle of the raceme and its pedicels are covered with purple-brown bristly hairs. Each flower is about 1" long and nearly as wide; it has a short tubular calyx and 5 petals. The calyx is covered with purple-brown bristly hairs and it has 5 teeth. The petals are arranged like a typical pea-flower: there is large upright banner, a pair of lateral wings, and a partially hidden keel (the latter consisting of two petals). There is a patch of pale yellow at the base of the banner. The blooming period occurs from late spring to mid-summer and lasts about a month. Fertile flowers are replaced by elongated seedpods about 2-3" long. The seedpods are somewhat flattened and covered with purple-brown bristly hairs. Each seedpod eventually splits open into two parts to release its seeds. The root system is rhizomatous, often forming vegetative offsets. Cultivation: This shrub adapts to full or partial sun, mesic to dry conditions, and various kinds of soil, including those that contain loam, clay-loam, or sand. It has a tendency to spread vegetatively and may be aggressive. Like other plants in this genus, it can increase the nitrogen levels of the soil.

Agati grandiflora (L.) Desv.:
Caribbean (Caribbean)
United States (North America)

Robinia hispida L.:
China (Asia)
United States (North America)
Canada (North America)

Robinia grandiflora L.:
India (Asia)

Robinia speciosa Ashe:
United States (North America)

Robinia grandiflora Ashe:
United States (North America)

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Bristly Locust has escaped from cultivation and has naturalized in different areas of Illinois (see Distribution Map). It is native to the hilly regions of southeastern United States, but will adapt to areas that are north of its original range. Habitats include thin upland woodlands, woodland edges, thickets, fence rows, roadside embankments, banks of drainage canals, vacant lots, and overgrown waste areas. Because of its attractive flowers and foliage, Bristly Locust is often cultivated as an ornamental shrub. Sometimes it is planted along embankments to control erosion.

Perennial, Shrubs, Woody throughout, Stems woody below, or from woody crown or caudex, Plants with rhizomes or suckers, Nodules present, Stems erect or ascending, Stems less than 1 m tall, Stems 1-2 m tall, Plants gland-dotted or with gland-tipped hairs, Stems solid, Stems or young twigs sparsely to densely hairy, Leaves alternate, Leaves petiolate, Stipules conspicuous, Stipules setiform, subulate or acicular, Stipules deciduous, Stipules free, Leaves compound, Leaves odd pinnate, Leaf or leaflet margins entire, Leaflets opposite, Stipels present at base of leaflets, Leaflets 5-9, Leaflets 10-many, Leaves glandular punctate or gland-dotted, Leaves hairy on one or both surfaces, Inflorescences racemes, Inflorescence axillary, Inflorescence or flowers lax, declined or pendulous, Flowers zygomorphic, Calyx 2-lipped or 2-lobed, Calyx hairy, Petals separate, Corolla papilionaceous, Petals pinkish to rose, Banner petal suborbicular, broadly rounded, Wing petals narrow, oblanceolate to oblong, Wing tips obtuse or rounded, Keel tips obtuse or rounded, not beaked, Stamens 9-10, Stamens diadelphous, 9 united, 1 free, Filaments glabrous, Style terete, Style hairy, Style hairy on one side only, Fruit a legume, Fruit stipitate, Fruit unilocular, Fruit freely dehiscent, Fruit elongate, straight, Fruit exserted from calyx, Fruit hairy, Fruit 3-10 seeded, Seeds reniform, Seed surface smooth, Seeds olive, brown, or black.

Bristly Locust has escaped from cultivation and has naturalized in different areas of Illinois (see Distribution Map). It is native to the hilly regions of southeastern United States, but will adapt to areas that are north of its original range. Habitats include thin upland woodlands, woodland edges, thickets, fence rows, roadside embankments, banks of drainage canals, vacant lots, and overgrown waste areas. Because of its attractive flowers and foliage, Bristly Locust is often cultivated as an ornamental shrub. Sometimes it is planted along embankments to control erosion.

In Great Britain and/or Ireland:
Fungus / parasite
Microsphaera pseudacaciae parasitises Robinia hispida

The nectar of the flowers attracts honeybees, bumblebees, and other long-tongued bees; occasional butterflies (which are poor pollinators), and possibly the Ruby-Throated Hummingbird. Miscellaneous insects feed on Robinia spp. in general or Robinia hispida (Bristly Locust) in particular, including the caterpillars of skippers and moths, stink bugs, leaf beetles, the larvae of long-horned beetles, and thrips (see Insect Table for a listing of these species). Birds and mammals apparently make little use of Robinia spp. as sources of food, although Bristly Locust may provide protective cover and habitat for bird nests. Photographic Location: Along a drainage canal at Kaufmann Lake Park, Champaign, Illinois.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Species: 3
Species With Barcodes: 1

Rounded Global Status Rank: G4 - Apparently Secure

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: N4 - Apparently Secure

Comments: Robinia hispida is native to the southern Appalachians, USA, and planted and occasionally escaped elsewhere. Isely (1998) recognizes five varieties; Kartesz (1999) follows this treatment. The var. rosea has sometimes been recognized as a separate species, R. boyntonii, and other species such as R. elliottii, fertilis, kelseyi, and nana have also sometimes been recognized.

Isely (1998) notes that this species "is evidently mostly an aggregate of sterile clones that reproduce vegetatively" with fertile plants "endemic in the mountains"; these cannot be distinguished from the sterile ones "except that they set fruit".

The presumed native range of the species, including all varieties, is Virginia, North Carolina, South Carolina, Georgia, Alabama, Tennessee, and perhaps Kentucky (cf. Isely, 1998); all reports elsewhere are presumably escapes from cultivation. LEM 4Jul01.