Osage-orange

Description

Osage-orange is a small to medium sized deciduous tree that is native to the Red River drainage basin of southern Oklahoma, southern Arkansas, the Blackland Prairies and Post Oak Savannas of eastern Texas, and the Chisos Mountains of western Texas. It has been planted as a hedge in all the 48 contiguous states of the United States and in southeastern Canada. It is now naturalized in the eastern half of the U.S. except along the northern border, and it occurs in scattered populations throughout the west.

Osage-orange is found in bottomland and upland forests, in bottomland and upland prairies, on the banks of rivers and streams, at the margins of marshes and ponds, and in pastures, thickets, fencerows, and roadsides. It is hardy to zone 4, which includes central Minnesota, but trees that far north may not reach full size and may suffer some branch dieback in severe winters.

Osage-orange is fast growing and 26′ to 66′ (8 to 20 m) in height. It usually grows too fast to be considered a shrub unless it is aggressively pruned for that purpose. It grows under full or partial sun in moist to moderately dry conditions. It is highly tolerant and will grow in almost any soil that is not highly acidic. In fertile soil, the root system is deep, in shallow soil it is very widespread, and where planted it is variable.

The trunk is short and often crooked, the branches are arching upward to spreading, and the crown is broad and rounded or irregular.

The bark is brown to dark orangish brown. It is shallowly furrowed with flat ridges when young. Older bark has deep furrows, and the ridges often peel into long, thin strips.

The twigs are zigzag and relatively stout. First-year twigs are bright green to greenish yellow and minutely hairy at first, becoming orangish brown and hairless with age. They have circular to oval, light-colored, pore-like openings (lenticels). They are armed with stout, straight, ⅜″ to 1″ (1 to 2.5 cm) long thorns in most leaf axils, especially those facing the sun. They exude a milky sap when cut. Second-year twigs sometimes form short spur branches with two to four leaves. The leaf scars are half-round, and the bundle scars are arranged in an oval.

There is no terminal bud. Lateral buds are often paired. The larger of the two is pale reddish brown, 1⁄32″ to 1⁄16″ (1.5 to 2 mm) long, globe-shaped, and covered by several scales. The scales are reddish-brown and have a fringe of minute hairs.

The leaves are alternate, but on short branches they appear more or less whorled. The leaf stalks (petioles) are ⅜″ to 1″ (1 to 2.5 cm) long and covered with short hairs. At the base of each petiole there is a lance-shaped, 1⁄32″ to 1⁄16″ (1.5 to 2 mm) long, leaf-like appendage (stipule), but these are shed at an early stage. The leaf blades are egg-shaped to narrowly egg-shaped, 1½″ to 4¾″ (4 to 12 cm) long, ¾″ to 2⅜″ (2 to 6 cm) wide, rounded at the base, and sharply pointed at the tip with concave sides along the tip (acuminate). The upper surface is medium to dark green, glossy, and hairless. The lower surface is pale and almost hairless, but with hairs along the midrib and veins. The margins are not lobed or toothed (entire).

Male (staminate) and female (pistillate) inflorescences are found on separate trees (dioecious). One to three clusters of staminate flowers appear in the leaf axils of short branches. Each cluster hangs from a hairy, ⅜″ to ⅝″ (10 to 15 mm) long stalk (peduncle). The clusters are globe-shaped or cylindric and ½″ to ⅞″ (13 to 22 mm) long.

Staminate flowers are about ⅛″ (3 to 4 mm) wide. They have 4 outer floral leaves (sepals), 4 stamens, and no petals. The sepals (together the calyx) are yellowish green, fused at the base, and separated into four lobes. The lobes are hairy, about 1⁄32″ (1 mm) long, and pointed. The stamens are about 1⁄16″ (2 mm) long, the anthers are yellow, and the stalks (filaments) are flattened and closely appressed to the sepals.

The pistillate inflorescence is a single globe-shaped head rising from a leaf axil on a 1⁄16″ (2.0 to 2.5 mm) long stalk (peduncle). The head is ⅜″ to ⅝″ (10 to 15 mm) in diameter but it appears larger due to the long stigmas. Each head has up to 200 appressed flowers that are compressed tightly together. Each flower has 4 sepals (calyx) and 1 style. The sepals are green, egg-shaped, and about ⅛″ (3 mm) long. They are fused at the base and separated into four long lobes. The lobes are inversely egg-shaped and they are densely hairy at the tips. Together they form a hood closely appressed and completely covering the ovary. The style has two branches. The base is green and about ⅛″ (3 mm) long and the branches are ⅛″ to ¼″ (4 to 6 mm) long. The stigmas are yellowish and unbranched.

The fruit is a fleshy, spherical, aggregate mass, 3½″ to 5½″ (9 to 14 cm) in diameter at maturity. It looks somewhat similar to an orange, but it is not edible. It secretes a milky juice when crushed. It is composed of numerous seed capsules (achenes), each one enclosed in a thickened, enlarged calyx, all of them fused together and sunken into the greatly enlarged receptacle. The surface is yellowish green to green, intricately wrinkled, with numerous rounded, raised projections (tubercles). There are often scattered, short, remains of the stigmas.

Height

26′ to 66′ (8 to 20 m)

Flower Color

Male flowers yellowish green, female flowers green

Similar Species

Habitat

Bottomland and upland forests, bottomland and upland prairies, banks of rivers and streams, margins of marshes and ponds, pastures, thickets, fencerows, and roadsides.

Ecology

Flowering

May to June

Pests and Diseases

Use

Osage-orange was used by European settlers as a hedge plant. With aggressive pruning, its dense growth and strong thorns create a thorny hedge that is “pig tight, horse high, and bull strong.” Following the mass production of barbed wire in the late 1870s, the hedges were mostly replaced by barbed wire fences.

The Great Plains Shelterbelt Project that began in 1934 was an attempt to reduce soil erosion after the severe dust storms in the Dust Bowl. By 1942, over 200 million trees were planted as windbreaks in a belt stretching from North Dakota to Texas. Many native trees and shrubs were used, along with a few non-native species. The native trees included green ash, Osage-orange, American elm, eastern cottonwood, hackberry, bur oak, red oak, eastern redcedar, ponderosa pine, and Rocky Mountain juniper.

The wood is the most decay-resistant of all North American timbers, and it is resistant to termites. It is often used for fence posts, but only when the wood is green. Aged wood is too hard to accept the staples.