tragacanth [key] or gum tragacanth, gummy exudation from the leguminous shrub Astragalus gummifer and related pulse family plants of SE Europe and W Asia. It is obtained through incisions in the stem of the plant. The gum is produced chiefly in Iran. Tragacanth is almost insoluble in water but swells in it to form a stiff gel. It is used as an emulsifying agent, as a component of pills, hand lotions, and medicinal lubricating jellies, as a demulcent, and as a sizing material. A gum (sometimes called Indian tragacanth) from a plant of the sterculia family is sold as a cheaper substitute. See gum.
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