Montana Field Guide

Plants: Annual, with separate male and female flowers on the same plant (monoecious). Stems 5-40 cm long and branched at the base, forming a prostrate mat. Foliage glabrous (not hairy) and green to reddish (Lesica et al. 2012). Leaves and stems often fleshy-swollen (Costea and Tardif 2003).

Leaves: Blades obovate to spatulate with wavy margins, 5–15 mm long, longer than the petiole (Lesica et al. 2012). Pale green with obvious veins and a notable short, sharp tip (mucro) (eFloras 2017). Stem leaves wither early, while axillary leaves are long-lived and much smaller (Henrickson 1993).

Inflorescence: Axillary glomerules (sessile clusters) with linear, spine-tipped bracts that are 1–1.5 mm long (Lesica et al. 2012).

(Contribution of Lesica et al. adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

Flowers July to October (Hitchcock et al. 1964).

All other Amaranthus in Montana except Prostrate Amaranth (A. blitoides) generally have an upright growth habit; most also have terminal inflorescences. Compared to A. blitoides, A. californicus has shorter sepals (1 mm or less)(Lesica et al. 2012). Also, California Amaranth has smaller seeds (less than 1.1 mm diameter), compared to Prostrate Amaranth’s 1.3-1.7 mm seeds (Hitchcock et al. 1964; Henrickson 1993).

Amaranthus albus can be confusingly similar to A. californicus, and herbarium specimens of the two have sometimes been misidentified. A. albus tends to be more upright, usually with a single rigid, pubescent stem and branches at wide angles, and it lacks fleshy leaves. Female flowers of A. californicus have one obvious tepal (sepal) with two others reduced or missing, with A. albus has 3 obvious tepals. A. californicus fruits tend to be mostly smooth-skinned and narrow abruptly to a long beak, while in A. albus they are wrinkled and narrow gradually to a shorter beak. A. californicus seeds are egg-shaped, and A. albus seeds are round or nearly so. The spiny bracteoles in the inflorescence are equal to the fruits in A. californicus, and longer in A. albus (1.5-2X the length of the fruit). However, several of these characters (tepals, fruits, seeds, and bracteoles) are known to overlap at times (Costea and Tardif 2003). See Costea and Tardif 2003 for comparative photos of fruits and seeds.

(Contribution of Lesica et al. adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

Vernally wet, often alkaline soil around ponds, roadsides; plains, valleys (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

In a study near a farm in central Saskatchewan, in which soil samples were collected from four different habitats and studied under laboratory conditions, Amaranthus californicus seeds sprouted from samples taken from agricultural sites in summer fallow and wheat stubble, but not from native prairie or grazed pasture (Archibold 1981). In summer fallow samples, the great majority of reproduction was annual or biennial forbs (96% of individuals per square meter). Of these forbs, a weedy mustard, Thlaspi arvense, made up more than half of the reproduction, and A. californicus made up roughly 2% of the total plants. This site had been in a wheat-fallow rotation. In the wheat stubble samples, the total sprouts of all species were less than a third of those in the summer fallow samples, but A. californicus made up roughly 6% of the total. Most reproduction was short-lived annual forbs (66%), with perennial forbs and annual grasses comprising the rest. Alfalfa (Medicago sativa) had grown on this site for a decade or more until the year prior to the study, which probably reduced the seed bank. The native prairie and grazed pasture, which lacked any germinating A. californicus, differed from each other in many respects, but both had lower numbers of short-lived forbs, higher numbers of perennial forbs, and substantial numbers of perennial grasses and sedges that sprouted vegetatively (45% on native prairie, 67% on grazed pasture).

Pollen from herbarium specimens of A. californicus and A. albus were indistinguishable in form, suggesting a close evolutionary relationship (Costea and Tardif 2003). Likely, A. californicus evolved from A. albus by an affinity for specific habitats such as dried-up lakebeds, though it now occurs in more disturbed habitats as is also typical for White Amaranth (Costea and Tardif 2003).

Flowers: Male flowers have 3 acute sepals that are similar in length to the bracts (Hitchcock et al. 1964). Female flowers have 1-3 unequal, acuminate sepals with the longest ca 1 mm long and like the bracts, and the other two small and scale-like or absent (Hitchcock et al. 1964; Lesica et al. 2012). There are no petals and 3 stamens, and the ovary is superior (Lesica et al. 2012).

Fruit: 1 mm, opening by a transverse line (circumscissile) (Henrickson 1993). A 2-3 mm long, green-lined utricle, longer than the sepals (Lesica et al. 2012). Seeds are hard, red-brown, and up to 1.1 mm across (Henrickson 1993).

(Contribution of Lesica et al. adapted from Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX)

All Amaranthus sp. have edible foliage and seeds (Thayer 2010).