Three Seeded Mercury Weed

Finally, I know who this fellow is, sort of. Acalypha…somebody, probably rhomboidea, commonly known as three-seeded mercury. He and his brothers are everywhere in my garden. This annual member of the Euphorbiaceae family starts as a thin, erect reddish stem with narrow leaves, about an inch to an inch and a half long, arranged opposite… Three Seeded Mercury Weed Rhomboid Mercury Acalypha rhomboidea Spurge family (Euphorbiaceae) Description: This annual plant is �–2′ tall, and usually unbranched. The central stem OMAFRA Crops

Know thine enemy: Three-seeded mercury

Finally, I know who this fellow is, sort of. Acalypha…somebody, probably rhomboidea, commonly known as three-seeded mercury. He and his brothers are everywhere in my garden.

This annual member of the Euphorbiaceae family starts as a thin, erect reddish stem with narrow leaves, about an inch to an inch and a half long, arranged opposite along the stem. As it grows, it branches, and leaves are arranged alternately. Here is where my ignorance of botany is exposed:There appear to be small yellow flowers at the leaf axils, but those yellowish bits I see could be bracts, or technically it might be an inflorescence …anyway, if you care to read details about the plant’s structure, you can read the description from the University of Guelph extension, or the Wikipedia site. For me, right now, I know I’m fairly close to identifying the plant.

This summer annual weed is not a nuisance, except that there’s a lot of it in my garden. It doesn’t reseed aggressively like hairy bittercress and it’s not difficult to eradicate. Despite the taproot, the plants are easy to pull. They are also said to be browsed by deer (not if there are phlox and hosta to eat, they’re not).

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According to the Southern Living Garden Problem Solver, which may or may not have misclassified this as Acalypha virginica (my plant definitely doesn’t look like the one shown by Illinois Wildflowers.info), many insects love to feed on the leaves. Thus, my sample, with its raggedy, chewn leaves should be pretty typical.

The seeds are supposed to be choice food for mourning doves, whom I would gladly welcome to my garden because I love their call. The buffet is open!

Three Seeded Mercury Weed

Rhomboid Mercury
Acalypha rhomboidea
Spurge family (Euphorbiaceae)

Description: This annual plant is �–2′ tall, and usually unbranched. The central stem has lines of fine white hairs, or is glabrous. The alternate leaves are up to 3�” long and 1″ across, with long narrow petioles that are slightly hairy. They are lanceolate or ovate, with bluntly serrated margins and conspicuous pinnate venation. There is a tendency for the leaves to congregate together near the top of the central stem, or any side stems that may be present. Where the petiole of each leaf meets the stem, there is a conspicuous bract that wraps around the inflorescence consisting of a green cyathium. This bract is slightly ciliate along the edges, and has 5-9 lobes. The cyathium contains tiny staminate and pistillate flowers without sepals and petals. The staminate flower is covered with yellow pollen, while the pistillate flower produces a 3-lobed spheroid fruit that is typical of the spurges. Each fruit contains three seeds. The blooming period occurs from about mid-summer until frost during the fall, and lasts one or more months. There is no floral scent. The root system consists of a central taproot.

Cultivation: The preference is light shade to full sun, and moist to slightly dry conditions. This plant often grows in fertile, loamy soil, but can tolerate gravelly or clay soil as well. This plant is easy and undemanding, and may volunteer spontaneously in a wildflower garden or ecological restoration. However, it is rather common and weedy.

Range & Habitat: The native Rhomboid Mercury occurs in every county of Illinois, and it is quite common (see Distribution Map). This is a rather inconspicuous plant that is easily overlooked because of the lack of showy flowers. Habitats include disturbed areas of moist prairies, limestone glades, openings or lightly shaded areas of floodplain forests, thickets, seeps, stream banks, ditches, fields, fence rows, roadsides, areas along railroads, vacant lots, poorly maintained lawns and gardens, and waste areas. This plant prefers moist disturbed areas.

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Faunal Associations: Like other members of the Spurge family that occur in Illinois, the seeds are attractive to such birds as the Mourning Dove and Greater Prairie Chicken; they may also be attractive to the Bobwhite, Horned Lark, and Wild Turkey. The herbaceous Acalypha spp. in Illinois lack the poisonous white latex of other members in the Spurge family, and their foliage is probably less toxic as a result. Deer are known to browse on Acalypha spp. occasionally, and it is possible that other mammalian herbivores do this as well. There have been reports of cattle being poisoned by these plants, possibly because of accumulation of nitrates in the foliage. It is unclear to me if the flowers of Acalypha spp. are wind- or insect-pollinated, although I suspect the former.

Photographic Location: The photographs were taken in a front yard along a roadside near Urbana, Illinois.

Comments: There are several Acalypha spp. in Illinois; the number of seeds per fruit can range from 1 to 3 (usually the latter), depending on the species. The species described here, Acalypha rhomboidea, is very similar to Acalypha virginica, except that the latter has 9-15 lobes in the bract that surrounds the inflorescence at the base of the petiole. Some authorities consider the former species to be merely a variety of the latter. The foliage of Acalypha spp. often becomes purplish tan during the fall, which has inspired the common name, ‘Copperleaf.’ This common name is often used in the agricultural industry.

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Ministry of Agriculture, Food and Rural Affairs

General Description: Annual, reproducing only by seed.

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Photos and Pictures


Three-seeded mercury.
A. Plant. B. Portion of fruiting stem showing 1 three-seeded fruit developing from 1 of 4 flowers in a leaf axil.

Stems & Roots: Stems erect, 7.5-100cm (3-40in.) high, simple or branched, slightly hairy; leaves green to bronze-green, 1-9cm (2/5-3½in.) long, lance- to rhombic-ovate on petioles that are 1/3 the length to almost as long as the leaf blade; margins with irregular, rounded teeth.

Habitat: Three-seeded mercury occurs in dry or moist soil in open woods, fields, waste places, ditches and roadsides throughout south-central Ontario.

Similar Species: It resembles young plants of Redroot pigweed but is distinguished by its flowers borne in axillary clusters with bracts having 5-9 lobes and its leaves occasionally a bronze-green colour.

Related Links

. on general Weed topics
. on weed identification, order OMAFRA Publication 505: Ontario Weeds
. on weed control, order OMAFRA Publication 75: Guide To Weed Control