Common Name: Tragacanth

General Information

Astragalus gummifer is a low-growing, thorny, deciduous shrub with spreading branches.
This plant is one of the many species of Astragalus that produce tragacanth gum - a substance with many uses in medicine, as a food additive and in industry. This species was often believed to be the main source of Tragacanth gum, but other species such as Astragalus gossypinus and Astragalus microcephalus are superior in quality and quantity[].

Known Hazards

Many members of this genus contain toxic glycosides[].
A number of species can accumulate toxic levels of selenium when grown in soils that are relatively rich in that element[].
All species with edible seedpods can be distinguished by their fleshy round or oval seedpod that looks somewhat like a greengage.[]

Botanical References

Range

W. Asia - Turkey, Syria, Lebanon, Iraq

Habitat

Dry sub-alpine slopes and valleys, occasionally below the tree line, 1200 - 2600 metres in Iraq[]. Upland forests and grassland[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Shrub
Height	0.20 m
Pollinators	Bees, Lepidoptera
Cultivation Status	Wild

Cultivation Details

Astragalus species that produce tragacanth gum are generally low-growing, spiny shrubs found in windy, usually semi-arid regions, often in mountaisn but also near the coast. They will often experience cold winters with frost, rain and snow and hot, dry summers. Most species grow in subarid areas with an annual precipitation of not more than 500mm, with a pronounced dry period of around four months in summer and most of the precipitation in winter. It is possible to grow many of these species outside of these habitats, especially in more continental climates. In moister climates, although they are likely to tolerate the low temperatures, they are unlikely to succeed if both summer and winter are wet unless the soil is very well-drained. Placing the plant in a local rain-shadow, such as the side of a building, can help successful cultivation[, ].
Tragacanthic Astragalus species generally prefer a gravelly soil with a small amount of fine earth[]. Requires a dry well-drained soil in a sunny position[]. Succeeds in poor soils[].
Requires a dry well-drained soil in a sunny position[, ]. Succeeds in poor soils[]. Tolerates a pH in the range 3.2 to 7.8.
Plants are intolerant of root disturbance and are best planted in their final positions whilst still small[].
This plant is a sub-shrub and although it produces woody stems these tend to die back almost to the base each winter.
The production of a special type of gum is an important economic feature of most tragacanthic species of Astragalus - the gum is sometimes exuded when the plants are wounded, but a better quality gum is obtained by incising or tapping the rootstock about 5 cm below the surface of the soil. The colour of the gum varies, both within and between species, from white to yellowish brown. The best quality gum is ribbon-like and translucent. The colour of gum, its amount and its shape depends on the species, collecting techniques and conditions[].
Plants are usually tapped after their second year of growth, and have a profitable gum life of around 7 years[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[]. Many members of this genus can be difficult to grow, this may be due partly to a lack of their specific bacterial associations in the soil[].

Edible Uses

A source of a high quality gum tragacanth - used as a thickener in confections, salad dressings, sauces etc[, , , , , ]. It is an approved additive to food and has the E number E413[].
Gum tragacanth, obtained mainly from the root, is used in the food industry primarily as a thickening agent, mainly in ice cream, candies, syrups, jellies, salad dressings and mayonnaise[, ].

Medicinal

Gum tragacanth is mucilaginous and emulsifier. It is sometimes used as a remedy for coughs[].
The gum is more commonly used in the pharmaceutical industry in the making of pills, tablets, and certain medicaments. Its principle medicinal role is as a mucilage to suspend heavy water-insoluble powders such as bismuth or zinc preparations[, ].

Gum tragacanth contains from 20 - 30% of a water-soluble fraction called tragacanthin (composed of tragacanthic acid and arabinogalactan). It also contains from 60 - 70% of a water-insoluble fraction called bassorin[].
Tragacanthic acid is composed of D-galacturonic acid, D-xylose, L-fructose, D-galactose, and other sugars[].
Tragacanthin is composed of uronic acid and arabinose; it dissolves in water to form a viscous colloidal solution[].
Bbassorin swells in water to form a thick gel[].

Other Uses

Gum tragacanth, obtained mainly from the root and stem, has a wide range of applications. The greatest demand comes from the textile industry in which the gum is used as a thickening in the preparation of boiled dyes for calico printing, in the application of textile dyes, for sizing yarns and threads, and in the dressing of silk fabrics and lace. It is also used in the printing trade; in the production of matches; the preparation of plastic materials; glue-making; to supply the gloss in water colours and ink; in perfumery; pencil manufacture, and in the paper industry, as a binding agent[, , ].
Cosmetically, it is used in toilet creams, jellies, lotions, dental creams, etc. It is also used in the production of superior sorts of soap[, ].
It can be used as an agar substitute in the preparation of nutrient media[].

Tragacanths are sometimes used as fuel in areas where wood is in short supply[].

Both the stems and the gum can be burnt as a fragrant incense[].

Propagation

Seed - best sown as soon as it is ripe in a cold frame[]. A period of cold stratification may help stored seed to germinate[]. Stored seed, and perhaps also fresh seed, should be pre-soaked for 24 hours in hot water before sowing - but make sure that you do not cook the seed[, ]. Any seed that does not swell should be carefully pricked with a needle, taking care not to damage the embryo, and re-soaked for a further 24 hours[, ]. Germination can be slow and erratic but is usually within 4 - 9 weeks or more at 13°c if the seed is treated or sown fresh[]. As soon as it is large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for their first winter, planting them out into their permanent positions in late spring or early summer, after the last expected frosts.