Common Name: Desert Ironwood

General Information

Olneya tesota is a spiny, evergreen shrub or small tree with a deep taproot; it can grow 8 - 10 metres tall. The trunk is gnarled, often several are produced as a result of trees being cut back by grazing or coppicing, they can have a diameter that often exceeds 45cm. Trees are more or less evergreen, but can drop their leaves during a drought[, , ].
The tree is harvested from the wild for local use as a food and source of wood. It has been suggested as a potential food crop for drier regions[]. A handsome flowering tree, it is also worthy of consideration as an ornamental[].

Known Hazards

Sawdust from this wood is reported to irritate the eyes and nose[].

Botanical References

Range

South-western N. America - southeastern California, southern Arizona and northwestern Mexico (Baja Norte, Baja Sur, Sonora).

Habitat

Dry desert watercourses, sandy and rocky soils of plains, slopes and along dry washes, where storm runoff increases the available moisture, often forming open woodland with other tree species; at elevations up to 900 metres[, ].

Properties

Edibility Rating
Other Uses Rating
Habit	Evergreen Tree
Height	9.00 m
Cultivation Status	Wild

Cultivation Details

Olneya tesota is a plant of drier to arid regions in southwestern N. America, growing in areas where summers can be very hot, up to 45°c, but winters are mild and frosts are few and not very heavy. Trees can sustain considerable damage at around -6°c[]. It is found wild in areas where the mean annual rainfall is around 75 - 400mm[].
Requires a sunny position in a well-drained soil[]. Prefers a pH in the range 7 - 8.5[].
Trees are of a moderate rate of growth, and can be quite fast growing if irrigated - there are reports of new shoots 150cm long[].
A fairly long-lived species, with specimens up to 200 years old reported[].
Trees are often cut back severely by grazing animals but usually resprout freely. Trees protected from grazing can be trimmed and coppiced, though very old wood will often fail to resprout[, ].
Flowering is usually prolific every 2 - 5 years[].
This is a rather variable species, especially with regard to the seeds and seedpods. Although only one bean in a pod is the rule on some trees, it usually is possible to find some pods with at least two or three beans. Many trees have pods with several seeds, and some are distinctly large-podded, to the extent of being nearly 13cm long and 10 - 12mm wide in the dry state. The largest pods seen had nine fully developed beans and two abortive, indicating that pods with eleven beans or more are sometimes produced[].
Some trees have relatively indehiscent pods that fall to the ground without shattering, while on other trees most of the pods open before falling, so that the individual beans have to be picked up, which takes much more time and labour[].
One tree found on a field trip had pods up to 13cm long and 12mm wide, with seeds up to 11mm long, 9mm wide and 8mm thick[].
Reports on the tree's ability to support nitrogen-producing bacteria on its roots are mixed. Trees growing wild in an Arizonan desert did not have root nodules, whilst trees grown from seed in Africa did have nodules[].

Edible Uses

Seed - raw or cooked[, , , , ]. Usually eaten cooked, the roasted seed has a flavour similar to peanuts[]. The seeds are usually dried, lightly roasted and then ground into a flour for use, though they are also eaten whole as a snack after roasting[]. On some trees, several seeds are produced in each seedpod, these seeds being around the size of peanuts with a similar taste and texture[].
The seeds are rich in protein (they contain around 19% protein, 61% carbohydrate and 10% fat) and have potential for use as a human food[]. The dried, powdered seed has a digestibility rating of 74%, increasing to 79% when cooked - this is higher than for many of the commonly eaten legume foods. The seeds do contain antinutritional factors, including trypsin inhibitors, phenols, alkaloids and haemagglutinin, but these are not present in high enough concentration to constitute a major nutritional problem. These antinutritional factors are soluble in saline solutions and can be removed by soaking or during cooking[].

The seeds have been used to make a beverage similar to hot chocolate[].

The fleshy young pods are eaten[]. The flavour is not bitter, even when eaten raw, though it can be somewhat astringent[].

Flowers[].

Medicinal

None known

Agroforestry Uses:

This species has a somewhat dense canopy and a very deep taproot - it often does not form any lateral roots for up to 2 metres. When growing in its desert habitat, this makes it an excellent companion tree in a mixed planting - its deep roots bring up nutrients from deep down to enrich the topsoil when it drops its leaves, whilst it provides little root competition for other plants growing close to it[].
Because of its preference for warmer sites, this species has been used as an indicator plant in choosing locations for citrus plantations[].

Other Uses

The heartwood is a rich brown and somewhat variegated; the thin layer of sapwood is yellowish white. The texture is medium coarse, grain is irregular, lustre is good, there is no distictive taste or odour when dry. The wood is very hard and strong - it is said to be as hard as ebony and can blunt a saw. The wood is also very heavy, sinking in water, and is durable, however it is also rather brittle[]. It is very difficult to work with hand tools, machine tools need to be kept sharp, it finishes smoothly and takes an excellent polish. Because the wood is not usually available in quantity, and even then usually only in small pieces, it is little used apart from making small objects such as gift items, pens and carvings[, , , ].
The wood makes a good fuel and an excellent charcoal[, ].

Propagation

Seed - it has a hard seedcoat and may benefit from scarification before sowing in order to speed up and improve germination. This can usually be done by pouring a small amount of nearly boiling water on the seeds (being careful not to cook them!) and then soaking them for 12 - 24 hours in warm water. By this time they should have imbibed moisture and swollen - if they have not, then carefully make a nick in the seedcoat (being careful not to damage the embryo) and soak for a further 12 hours before sowing. The optimum temperature for germination appears to be 25 - 30. Fresh seeds often have 80 - 90% germination rate with emergence usually occurring in 4 - 12 days.
Young seedlings quickly form a taproot and become very difficult to transplant. It is best, where possible, to sow the seed in situ, and protect carefully from predators such as mice and rabbits. If sown in containers, then the seedlings should be transplanted to individual, deep containers as soon as they are large enough to handle, and be planted out into their permanent positions as soon as there is any sign of the taproot reaching the bottom of the container[].