Rose Acacia or Bristly Locust
Robinia hispida
From Illinois Wildflowers
This introduced shrub is 3-10' tall and across, branching abundantly. Young branches are green andvery bristly-hairy. These long bristly hairs are purple-brown and sticky from minute glands. Alternate compound leaves 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 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.
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