Indigofera pseudotinctoria Seeds | False Indigo
LATIN NAME: Indigofera pseudotinctoria
COMMON NAME: False Indigo
Plant Profile
In the open it is a low, spreading, many-branched shrub a metre to a metre and a half tall, with alternate pinnate leaves of many small oval leaflets and upright racemes of pink to reddish-purple pea flowers through summer, followed by slender round pods that rattle when dry. The whole plant is typical of the indigo genus in form, which is the root of the naming mix-up, but the leaf is finer and the bush tidier than the coarse tropical dye species, and the stem stays green rather than woody at the base.
The isoflavone pseudobaptigenin, named from the related false indigo baptisia, shows up in the root bark of indigofera species and is a useful marker for telling them apart in the herbarium. It is not a dye and not a drug in the kitchen sense, but it is exactly the sort of compound that taxonomists use to confirm a collection and that biochemists screen for activity.
Science & Biotechnology
The chemistry that interests phytochemists here is the isoflavone set rather than the dye pathway. The roots and leaves carry isoflavones such as pseudobaptigenin and genistein-type compounds, the same broad class that makes soy and other legumes a focus of nutrition research. These are present at modest levels and are studied more than they are used, but they explain why the plant is sampled in forage and soil-quality work.
Uses & Benefits
The name false indigo is a warning label, not a description. This plant was long lumped with the true dye indigos because it wears the same pea flowers and the same compound leaf, but it does not yield the blue that the trade wanted, and anyone who grew it for a dyebath came away with a brownish liquor and no indigo. The useful relatives for colour are Indigofera tinctoria and Indigofera suffruticosa; this species earns its place in the garden and the field for other reasons entirely.
The blue of indigo comes from indican, a glucoside stored in the leaf that is fermented and oxidised into indigotin. The true dye species load the leaf with indican; this one does not, so the same process gives little or no blue. The confusion is old and commercial, because the plants look alike in a field and the genus name invites the mistake. The honest label is a green-manure and soil plant, not a colour crop, and that is how it should be sold.
As a member of the pea family, the plant feeds soil as well as itself. Nodules on the roots host rhizobia that pull nitrogen from the air and pass it to the plant, and when the leaves fall or the stems are cut and left to rot, that nitrogen is released to neighbours. This is the basis of its value on poor, eroding ground, where a legume cover beats a bare slope for keeping the soil in place.
In practice the shrub is grown for its dense, many-branched form that smothers weeds and holds banks, for a little autumn forage where livestock browse the tips, and for the pink to reddish-purple racemes that brighten a dry border. It is browsed but not a major fodder, and it is at its best as a low, flowering ground cover that needs almost no input once it is set.
To use it as a living mulch, sow a band along the contour of a slope so the stems knit into a net that slows runoff, or underplant it with taller perennials where a green floor is wanted. It tolerates shearing, so it can be mown lightly to keep it low, and the cut material is returned as mulch. On a roadside it is one of the cheaper ways to keep a cut bank from washing out.
Growing from Seed
Seed has a hard coat and benefits from a little help before it will take, but once up the plant is undemanding. Sow in spring into a warm, sunny seedbed, and plan to thin the seedlings so the bushes have room to branch rather than race each other for light.
Nick the seed coat lightly or pour hot-but-not-boiling water over it and let it cool, then sow one centimetre deep in a sandy loam and keep it moist. The first leaves are the pinnate type with several small oval leaflets, and the seedling stands upright and slender. Prick the young plants into individual pots once they hold four true leaves, and harden them before setting them out.
Cut the stems back by a third after the main flower flush to keep the bush dense and to push fresh leafy growth that makes the best green manure. In autumn, after the pods set, cut the whole plant to near the base where it is grown as a soil crop, and leave the roots to rot and feed the ground. The shrub returns from the crown each spring and needs no staking.
Our Take
If you actually want blue, grow the true dye species Indigofera tinctoria, and for a showier wild indigo try Indigofera amblyantha; this false indigo is the one to plant where the job is holding soil, not colouring cloth.
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