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three seeded mercury weed

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.

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

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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.

Flowers & Fruit: Flowers in greenish clusters in axils of leaves, each cluster composed of one or more palmately cleft bracts with 5 to 9 lobes, one or more stalked male spikes 4-15mm (1/6-2/5in.) long and one or more shorter female flowers; seedpods deeply 3-lobed (similar to those of Leafy spurge) and containing 3 seeds; seeds tan coloured, 1.6-1.8mm (1/15in.) long. Flowers from July to September.

General Description: Annual, reproducing only by seed.

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).

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.

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, many insects love to feed on the leaves. Thus, my sample, with its raggedy, chewn leaves should be pretty typical.

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.

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!