Amaranthus retroflexus L.

Family: Amaranthaceae

Pertinent Synonyms & Notes (particularly those used in California; go to GRIN for other synonyms)

Amaranthus tricolor L.

Pertinent Common Names (particularly those used in California; go to GRIN for other common names)

redroot pigweed, rough pigweed

Primary Disseminule Type


Description (diagnostics are in brown)

Fruit a dehiscent (circumscissile) utricle, broadly obovoid to broadly elliptic, 1.5–2.5 mm long, smooth or slightly rugose, with 5 attached tepals (tepals obovate to spoon-shaped, subequal, (2)2.5–3.5(4) mm long, apex rounded to slightly notched or mucronulate), containing 1 seed.

Seed elliptic to obovate in outline, somewhat compressed with an obtuse marginal rim, cross-section elliptic to lens-shaped or barely fusiform, with a protruding notch along the margin where hilum occurs and from which a shallow depression runs inward for a short distance, 0.9–1.3 mm diameter x 0.6–1 mm thick. Surface shiny, ± smooth (under magnification, looking cobblestone-like, as well as pitted and punctate in some spots), dark reddish-brown to black.

Hilar region round to elliptic, consisting of a linear slit between two semi-circular scars.

Embryo annular, surrounding copious perisperm.

Similar Species

Similar Species Comparison Chart

Risk Assessment (codes in yellow or red indicate cause for concern; assessments are current as of mid-2011; click AUQP, NZBORIC, or NZBPI for access to the most recent versions of these databases and possible assessment changes)