Redroot pigweed-Amaranthus retroflexus L.-Poisonous plant

Redroot pigweed

General poisoning notes:

Redroot pigweed (Amaranthus retroflexus) is a naturalized herb that is found across much of Canada. This plant can cause a variety of toxic problems, including perirenal edema in pigs. However, the nature of the toxic compound is not known. This plant can also accumulate oxalates to as much as 30% of dry weight. Redroot pigweed is capable of accumulating toxic concentrations of nitrates (Osweiler et al. 1985).

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 retroflexus L.

Vernacular name(s): redroot pigweed

Scientific family name: Amaranthaceae

Vernacular family name: amaranth

Geographic Information

Alberta, British Columbia, Manitoba, New Brunswick, Northwest Territories, Nova Scotia, Ontario, Prince Edward Island, Quebec, Saskatchewan.

Toxic parts:

Leaves, stems.

Notes on Toxic plant chemicals:

Nitrates have the following LD₅₀ values (Crawford et al. 1966):

LD₅₀ 1.0 g/kg body weight in cattle

LD₅₀ 0.5 g/kg body weight in other ruminants.

Acute poisoning occurs when forage nitrates exceed 1.0% nitrate (dry weight) or 1500 ppm in water (Osweiler et al. 1985). All Amaranthus spp. mentioned in this information system can accumulate toxic quantities of nitrates.

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:

abortion

bloat

blood brownish

breathing, rapid

death

dyspnea

kidney, edema of

mucous membrane, brown

nephrosis, severe

nervousness

recumbency

recumbency, ventral

regurgitation

weakness, posterior

Swine

General symptoms of poisoning:

ataxia
death
gait, crouching
kidney, edema of
nephrosis, severe
recumbency, ventral
trembling
weakness.