Annual, reproducing only by seed.
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 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.
Three-seeded mercury occurs in dry or moist soil in open woods, fields, waste places, ditches and roadsides throughout south-central Ontario.
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.
The rounded cotyledons and distinctive colouring of three seeded mercury
Seedling plant in a corn field.
Three-seeded fruit developing