Amaranthus tricolor Seeds | Joseph’s Coat
LATIN NAME: Amaranthus tricolor
COMMON NAME: Joseph’s Coat
Plant Profile
The plant is a fast, soft-stemmed annual, usually half a metre to a metre tall, with ovate leaves on long stalks and small green or red flowers packed into dense, bristly spikes. The fruit is a utricle — a dry one-seeded capsule that opens by a lid dropping off — and each holds a single glossy black seed barely a millimetre across.
Betalain biosynthesis starts from tyrosine, which is converted to L-DOPA and then split by DOPA 4,5-dioxygenase into betalamic acid, the central building block of the whole family. Condensing betalamic acid with an amine gives a yellow betaxanthin such as indicaxanthin; condensing it with cyclo-DOPA, made by a cytochrome P450, gives a red-violet betacyanin. In Amaranthus tricolor the main betacyanin is amaranthin, a glucuronosylated betanidin, accompanied by betanin and their isomers.
The grain species — Amaranthus hypochondriacus, Amaranthus cruentus and Amaranthus caudatus — carry a protein rich in lysine, and their oil is the richest known plant source of squalene, a triterpene used in cosmetics and in vaccine adjuvants. Amaranth grain also supplies a lunasin-like peptide.
As a vegetable the plant is a cut-and-come-again crop. Shoots are cut young and tender, steamed briefly or stirred into soups, and the red forms are used where their colour is the point. Oxalate and nitrate accumulate in the leaves, so the crop is not usually eaten raw in quantity and the water from boiling is discarded.
Cut the stand about a hand’s width above the ground, leaving the lowest buds to regrow; the bed can be cut repeatedly through the warm season if it is fed after each pass. Grain amaranth is harvested when the seed heads rattle, then dried and winnowed.
Science & Biotechnology
Betacyanins are water-soluble and stable enough to survive cooking, so amaranth leaf extract has long been used as a kitchen colourant, stirred into dough, rice or pickles for a pink tint. The same chemistry makes the pigment easy to assay: it absorbs in the green band and shifts colour with pH.
The weedy amaranths share the genus and the C4 photosynthetic pathway, which uses the NAD-malic enzyme type and gives them fast growth in heat and drought. The same vigour has made Amaranthus retroflexus and Amaranthus palmeri notorious in maize and cotton fields, where resistance to several herbicide groups has appeared. Volunteer amaranth in a following crop is worth removing early.
Uses & Benefits
Gardeners meet this species as an ornamental bedding plant, a tropical leaf vegetable and a weed-patch cousin at the same time. Linnaeus and his successors described it more than once, which is why Amaranthus gangeticus, Amaranthus mangostanus and Amaranthus tristis still turn up in seed lists as if they were separate plants. All three are now sunk into Amaranthus tricolor, a species grown for its leaves rather than its grain, and it sits in the same genus as the tall grain amaranths of Mexico and the Andean valleys.
In the ornamental forms the leaf base stays green while the upper half carries yellow, orange or crimson, and the pattern intensifies as the shoot matures. That gradient is a useful field character: seedlings start green and colour from the tip downward, so a bed reads as an even colour block only after the plants reach their full size.
Growing from Seed
The seed is tiny and the seedlings are fragile in cold, wet ground, so the crop belongs in the warm part of the season and in a fine, level seedbed.
Flea beetles pit the leaves of young plants and can set a bed back badly; row cover until the plants are half grown solves most of it. Aphids cluster on the growing tips, and leaf miners scar the older leaves. Amaranths are heat lovers — a hot, dry week only makes them grow faster.
Our Take
If the colours are what you want, the drooping crimson tassels of love-lies-bleeding are the same family trick at a larger scale, and the wheat-coloured plumes of celosia will hold their shape longer in a vase. For a green-leafed slicing type, green amaranth bolts more slowly than the ornamentals.
Related Reading
More species in the same orbit as Joseph’s Coat: