Kansas Wildflowers and Grasses - Rydberg’s poison ivy

RYDBERG’S POISON IVY

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Toxicodendron rydbergii (Small ex Rydb.) Greene

Scott County, Kansas

Height: 12-80 inches

Family: Anacardiaceae - Cashew Family

Flowering Period: May, June

Also Called:

Western poison ivy.

Trunks:

Shrubs, dioecious; stems ascending or erect, spreading by underground suckers; branches without aerial roots. Bark gray, +/- ribbed; wood yellowish brown, soft.

Twigs:

Light brown, glabrous or glabrescent, flexible; leaf scars crescent-shaped; pith white; buds brown, ovoid, 1/8 to 1/6 inch, scales tawny-tomentose.

Leaves:

Deciduous, alternate, 3-foliolate; stipules absent; petiole 1.2 to 4.8 inches long, glabrous or sparsely pubescent, especially along edges; leaflets: lateral petiolules 1/12 to 4/5 inch, terminal petiolule 2/5 to 1 1/5 inch, blade ovate to rhombic or suborbiculate, 1 3/4 to 6 inches long, 1 1/5 to 3 1/5 inches wide, base truncate to tapered, often inequilateral in lateral leaflets, margins irregularly dentate or undulate, apex acuminate, lower surfaces light green, glabrous or appressed-strigose, upper surfaces green to yellowish green, glabrous, glabrate, or appressed-strigose along midrib.

Flowers:

Inflorescences axillary on current-year growth, spreading or erect, panicle-like, narrowly to broadly ovoid, 2/5 to 1 3/5 inch, 5-40-flowered; peduncles 1/8 to 3/5 inch, sparsely appressed-strigose, glabrescent; pedicels 1/25 to 1/10 inch. Flowers unisexual, radially symmetric; sepals 5, connate proximally, green, triangular, 1/25 to 1/16 inch; petals 5, distinct, greenish yellow, lanceolate to ovate, 1/12 to 1/8 inch; staminate: stamens 5; pistillate; pistil 1, styles 3; stigmas 3, capitate.

Fruit:

Fruits July-September; drupes, yellowish white, globose or subglobose, 1/8 to 1/4 inch long, 1/6 to .28 inch wide, glabrous, glossy; stone 1, yellow or yellowish white, subglobose, 1/8 to 1/5 inch long, 1/4 to 1/4 inch wide, low-ribbed, resin ducts black.

Habitat:

Rocky prairie hillsides, stream banks, floodplains, bluffs, open woods, ravines, roadsides.

Distribution:

West 3/5 of Kansas

Origin:

Native

Comments:

Mature fruits of both Toxicodendron rydbergii and Toxicodendron radicans often remain on the plants into and sometimes through winter. Named for American botanist Per Axel Rydberg.

Rydberg’s poison ivy habit