Perennial herb to 1.5 m. high, creeping basal parts up to 30 cm. long, with bundles of roots; stems erect, one or a few from the rhizome, branching only in the lower 1/4, branches with leaves only; main stem angular, densely pubescent.. Leaves in the lower part of the main erect stems opposite, in whorls of 3(–4) or alternate, generally larger than at the tip of the stem, especially at the inflorescence, where they are generally verticillate.. Lower cauline leaves subsessile or very shortly pedicellate, ovate to lanceolate, up to 4 cm. long and 1 cm. wide or wider, rugulose, base cordate to subcordate, margin entire, setulate to serrulate, apex acute to acuminate; lateral nerves ± 2 pairs, basal pair reaching almost the leaf-apex lamina; leaves of branches opposite, lamina broader and shorter than on those of the main stem, apex bluntly acute.. Inflorescence bisexual clusters, axillary.. Male flowers shortly pedicellate, 5-merous, with a marked transverse dorsal crest on each tepal, bearing a few scattered hairs; rudimentary ovary present.. Female flowers: perianth 4-toothed at apex, with 8–10 clearly marked longitudinal ridges; ovary completely enclosed, and only the ± 0.7 mm. long filiform style protruding.. Achene shiny black, ovoid, ± 1 mm long.
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