Ironwood flowers and seeds are
edible. Desert Ironwood flowers can be eaten raw in salads or candied for use
in desserts. Although the seeds can be eaten raw, both green and dry/brown
stages of seeds may be most easily digested when blanched, sprouted or cooked
(1, 2). The flowers bloom in late April-May and seed pods set in June-July.
When they are ripe, they are easier to gently shake free from the limbs. If
harvesting green pods, plunge the pods into boiling water and then transfer to
ice water to clean them. Drain, dry and package them in sealed plastic
(anaerobic) containers marked with the date of harvest (1).
Seeds are usually eaten cooked or dried,
lightly roasted and then ground into a flour before use, though they are also
eaten whole after roasting (4, 6). The seeds have been used to make a beverage
similar to hot chocolate (6). The pods
have a slightly sweet and nutty flavor with some astringency but become more
flavorful when left to ripen on the tree (1, 2). Some describe the taste and
texture of the seed as similar to the taste of peanuts (5, 6). They are very
high in protein (~ 19% protein) as well as carbohydrate (~61%) and fat (~10%)
(6). The dried, powdered seed has a higher digestibility rating (74% for
uncooked and 79% for cooked seeds) compared to other legume beans (6). As such,
ironwood seeds may have potential to be commercially produced for human food
(6). The seeds do, however, contain small
amounts of trypsin inhibitors, phenols, alkaloids and haemagglutinin, known
collectively as “antinutrients” but these are soluble and removed with soaking
or cooking (6).
Ironwood is the tallest growing
tree in the Sonoran Desert and provides a beneficial micro-habitat for many
desert species. As such, these are considered “nurse” trees in the Sonoran
Desert (4). Animals gather in the shade during the hottest months and other
cacti and small shrubs utilize the tree's canopy as shelter from the sun. Like
other members of the family Ironwood, it is a tree that gathers nitrogen from
the soil, so leaf litter and seeds are particularly rich in nutrients. Desert
animals also consume the seeds, and livestock browse the foliage. Seeds eaten
by desert animals; plant browsed by bighorns.
Ironwood, in natural populations,
has a very deep taproot allowing it to access water in the cooler soil depths
(6). This factor, along with its ability to fix nitrogen makes it an excellent
companion tree in a mixed planting (6). Additionally, it generally produces
very few branched roots near the soil surface, bringing water and nutrients
from deep down with its taproot to enrich the neighboring plants which have a
more shallow root system (6). It further adds nutrients to the surface when it
drops its leaves (6). Because of its
preference for areas with mild winters, it is considered an indicator in
selecting favorable sites for citrus orchards, mild winters (4, 6).
Olneya tesota is known
locally in the Sonoran desert as "Ironwood" or by the Spanish common
name palo de hierro. These names point to the use of ironwood trees are the
source of very dense, hard wood. The heartwood is a rich brown and somewhat
variegated and the sapwood provides a thin layer of yellowish white, having an
irregular grain with a good luster when polished (4, 6). The wood is very hard
and strong (reportedly as hard as ebony) and is dense/heavy enough to sink in water
(6). Only leadwood (Krugiodendron ferrum (Vahl) Urban), a small tropical
tree of southern Florida, is heavier (4).
The hardness makes it difficult to work with using hand tools and even
machine tools have trouble keeping a sharp blade, it is used for making small
objects such as gift items, pens and carvings and for fuel and charcoal (4, 6). Native cultures in both Arizona and Sonora made use of the wood for building as
well as for making small carved items (2).
