Acalypha monococca (Engelm. ex A. Gray) Lill. W. Mill. & Gandhi

One-Seeded Mercury


CC = 3
CW = 5
MOC = 71

© SRTurner

Family - Euphorbiaceae

Habit - Taprooted, monoecious, annual forb.

Stem - Strongly ascending to erect, to 50 cm, pubescent with short, curved hairs. Plants annual, taprooted, with clear sap.

Acalypha_monococca_stem2.jpg Stem and leaves.

© SRTurner

Acalypha_monococca_stem.jpg Stem and inflorescences.

© SRTurner

Leaves - Alternate, short-petiolate, with the petiole 1/4 the length of the blade or less, usually shorter than the inflorescence bracts. Stipules present but minute and deciduous. Blades to 7 cm, linear to lanceolate, much longer than wide, the margins entire or with a few blunt, minute teeth, surfaces pubescent with short, loosely appressed hairs.

Acalypha_monococca_leaf1.jpg Leaf adaxial.

© SRTurner

Acalypha_monococca_leaf2.jpg Leaf abaxial.

© SRTurner

Inflorescences - Entirely axillary, 1-3 per node, usually with 1 basal pistillate node below few to several nodes of staminate flower clusters, the tip of the staminate spike usually extending well beyond the bracts. Bracts 1 per pistillate node, leafy, folded longitudinally around the inflorescence, with 9-17 lobes, the margins and outer surfaces moderately hairy, with some of the hairs usually gland-tipped, also with sparse to moderate minute, reddish, sessile glands.

Acalypha_monococca_inflorescences.jpg Inflorescences.

© SRTurner

Acalypha_monococca_inflorescence.jpg Inflorescence.

© SRTurner

Fruits - 1.8-2.6 mm long, 1-locular, 1-seeded, the surface moderately hairy and occasionally alsowith sparse, minute, sessile glands, lacking tubercles at maturity. Seeds 1.6-2.4 mm long.

Flowering - May - October.

Habitat - Glades, upland prairies, sand prairies, ledges, savannas, forest openings, railroads.

Origin - Native to the U.S.

Lookalikes - A. gracilens and other species of Acalypha.

Other info. - This common species of mercury inhabits drier habitats than the others. In general appearance it is similar to A. gracilens, which also has narrow leaves. It is easily distinguished from that species by its single-seeded fruits, which are round in profile rather than three-lobed. Although not particularly showy, it is usually found in less disturbed areas and is therefore a welcome find. Missouri is near the northern end of the plant's range, which extends southward through lower Texas.

The common name "mercury" comes from the Roman god of that name, due to the fancied resemblance of the plant's inflorescence bracts to the god's winged sandals.

Photographs taken at LaBarque Creek Conservation Area, Jefferson County, MO, 8-28-2018, and Rockwoods Reservation, St. Louis County, MO, 9-3-2018 (SRTurner).