Cleome serrulata Pursh

Rocky Mountain Bee Plant


CC = 2
CW = 3
MOC = 3

© SRTurner

Family - Cleomaceae

Habit - Annual forb.

Stem - Ascending to erect, to 2 m, unbranched or sparsely branched above, glabrous or with sparse cobwebby hairs at nodes when young.

Cleome_serrulata_stem.jpg Stem and nodes.

© SRTurner

Cleome_serrulata_stem2.jpg Stem and leaves.

© SRTurner

Leaves - Alternate, trifoliate, petiolate, stipulate, glabrous to moderately pubescent with cobwebby hairs. Petioles 3-4 cm long. Stipules herbaceous or scalelike, inconspicuous, linear, 0.2-0.8 mm long, withering as the leaves mature. Leaflets mostly 2-5 cm long, narrowly elliptic to lanceolate, narrowed or tapered to a sharply pointed base and tip, the margins entire.

Cleome_serrulata_leaf1.jpg Leaf adaxial.

© SRTurner

Cleome_serrulata_leaf2.jpg Leaf abaxial.

© SRTurner

Inflorescences - Dense terminal racemes, to 25 cm, the flowers subtended by bracts, these 8-12 mm long, 1-2 mm wide, simple, short-stalked to sessile, narrowly elliptic to lanceolate, tapered to a hairlike tip, usually glabrous. Flower stalks 10-12 mm long, glabrous.

Cleome_serrulata_inflorescence.jpg Inflorescence.

© SRTurner

Cleome_serrulata_inflorescence2.jpg Inflorescence.

© SRTurner

Cleome_serrulata_ff.jpg Flowers and fruits.

© SRTurner

Flowers - Sepals fused to at or above the midpoint, 2.5-3.0 mm long, the free portion triangular-ovate, glabrous. Petals spreading asymmetrically, similar in size and shape, 7-12 mm long, 2-4 mm wide, abruptly narrowed to a stalklike base 1-2 mm long, pink to purple. Glandular disc fleshy, short-cylindrical, 1-4 mm long, with a scalelike appendage ascending from the tip. Stamens with the filaments 1.2-1.8 cm long, the anthers 1.5-2.0 mm long, linear. Gynophore short at flowering (0.2-0.4 cm) but elongating as the fruit matures to 1.0-2.5 cm long.

Cleome_serrulata_calyces.jpg Calyces.

© SRTurner

Cleome_serrulata_corolla.jpg Corolla.

© SRTurner

Fruits - Capsules 2-5 cm long, 2-3 mm wide, linear, on a long gynophore, usually slightly constricted between seeds, glabrous. Seeds 2.5-4.0 mm in diameter, the surface appearing wrinkled or warty, dark brown to black with lighter-colored warts and faint concentric lines.

Cleome_serrulata_fruits.jpg Fruits.

© SRTurner

Flowering - July - August.

Habitat - Loess hill prairies, railroads, open disturbed areas.

Origin - Native to the U.S.

Lookalikes - Cleome hassleriana.

Other info. - This attractive plant is rare in Missouri, except where cultivated. The state lies near the far eastern extent of the plant's natural range, which includes most of the western half of the continental U.S. It is easily recognized by its dense and showy inflorescences with numerous long, protruding stamens, and trifoliate leaves. As the plants mature, a distinctive array of long, narrow fruits on long stalks is produced. The lookalike C. hassleriana has palmately compound leaves with 5 or 7 leaflets. Species in this genus are commonly grown as ornamentals and nectar sources for bees. Native Americans used the plant as a poultice for treatment of a variety of ailments.

Another name for this species is Peritoma serrulata (Pursh) DC.

Photographs taken along Hwy 26 in Morrill County, Nebraska, 8-13-2019, and at Hot Springs State Park, WY, 7-27-2021 (SRTurner).