Smooth pigweed-Amaranthus hybridus L.-Poisonous plant

Smooth pigweed

General poisoning notes:

Smooth pigweed (Amaranthus retroflexus) is a naturalized herb found in waste places across Canada. Ingesting this plant has caused nitrate poisoning of cattle in New Zealand. No other literature references to poisoning were found (Duckworth 1975).

Description

Plants densely to moderately pubescent, especially distal parts of stem and branches. Stems erect, reddish near base, branched in distal part to simple 0.2-1.5(-2) m; underdeveloped or damaged plants rarely ascending to nearly prostrate. Leaves: petiole ¹/2 to equaling blade; blade ovate to rhombic-ovate, 2-15 × 1-7 cm, base cuneate to rounded-cuneate, margins entire, plane or slightly undulate, apex acute, obtuse, or slightly emarginate, with terminal mucro. Inflorescences terminal and axillary, erect or reflexed at tip, green or silvery green, often with reddish or yellowish tint, branched, leafless at least distally, usually short and thick. Bracts lanceolate to subulate, (2.5-)3.5-5(-6) mm, exceeding tepals, apex acuminate with excurrent midrib. Pistillate flowers: tepals 5, spatulate-obovate, lanceolate-spatulate, not clawed, subequal or unequal, (2-)2.5-3.5(-4) mm, membranaceous, apex emarginate or obtuse, with mucro; style branches erect or slightly spreading,; stigmas 3. Staminate flowers few at tips of inflorescences; tepals 5; stamens (3-)4-5. Utricles broadly obovoid to broadly elliptic, 1.5-2.5 mm, shorter than or subequal to tepals, smooth or slightly rugose, especially near base and in distal part, dehiscence regularly circumscissile. Seeds black to dark reddish brown, lenticular to subglobose-lenticular, 1-1.3 mm, smooth, shiny.

Nomenclature:

Scientific Name: Amaranthus hybridus L.

Vernacular name(s): smooth pigweed

Scientific family name: Amaranthaceae

Vernacular family name: amaranth

Geographic Information

Ontario.

Toxic parts:

Stems.

Notes on Toxic plant chemicals:

Smooth pigweed (Amaranthus hybridus) has caused poisoning of cattle from nitrate accumulation. All the Amaranthus spp. listed in this information system are nitrate accumulators. In serious cases, poisoning and death can occur (Duckworth 1975, Osweiler et al. 1985).

Toxic plant chemicals:

Nitrate.

Animals/Human Poisoning:

Note: When an animal is listed without additional information, the literature (as of 1993) contained no detailed explanation.

Cattle

General symptoms of poisoning:

blood brownish

death

gait, unsteady

mucous membrane, brown

nervousness

Notes on poisoning:

In one case in New Zealand, cattle were poisoned and one died as a result of suspected nitrate poisoning after ingesting smooth pigweed. The mucous membranes were brown and the blood was dark. The animals were unsteady. Postmortem findings showed the rumen to be full of the plants, but no obvious lesions were present (Duckworth 1975).

Prevention:
To prevent pigweed poisoning, do not allow animals to have access to affected pastures, especially if the animals are hungry. Spray or mow plants down, making sure they are dead before animals are on pasture. Provide for supplemental feed if pasture quality is poor, since well-fed animals are less likely to consume pigweed.