【医】 靛灰叶, 野靛草

[ noun ]
much-branched erect herb with bright yellow flowers; distributed from Massachusetts to Florida
<noun.plant>

Indigo \In"di*go\, n.; pl. {Indigoes}. [F. indigo, Sp. indigo,
indico, L. indicum indigo, fr. Indicus Indian. See {Indian}.]
1. A kind of deep blue, one of the seven prismatic colors.

2. (Chem.) A blue dyestuff obtained from several plants
belonging to very different genera and orders, such as,
the woad, {Isatis tinctoria} (family {Cruciferae}),
{Indigofera suffroticosa}, {Indigofera tinctoria} (family
{Leguminosae}), {Indigofera Anil}, {Nereum tinctorium},
{Polygonum tinctorium} Ait. (family {Polygonaceae}), etc.;
called also {natural indigo}. It is a dark blue earthy
substance, tasteless and odorless, with a copper-violet
luster when rubbed. Indigo does not exist in the plants as
such, but is obtained by decomposition of the glycoside
{indican}.

Note: Commercial indigo contains the essential coloring
principle indigo blue or indigotine, with several other
dyes; as, indigo red, indigo brown, etc., and various
impurities. Indigo is insoluble in ordinary reagents,
with the exception of strong sulphuric acid.

{Chinese indigo} (Bot.), {Isatis indigotica}, a kind of woad.


{Wild indigo} (Bot.), the American herb {Baptisia tinctoria}
which yields a poor quality of indigo, as do several other
species of the same genus.