Yesterday in the dusty landscape of Northern Kenya, we saw a tree which was turning green and flowering even though it has not rained in months. The locals say that the greening of this Acacia species means that the rains are coming soon. This is just amazing to me. How and why would a tree be able to anticipate that rain was coming and be so sure that it would produce leaves and flowers? What possible molecular mechanism can explain this? The indigenous people don’t care so much for a mechanism. They are willing to just accept the fact that their local Acacia species (nilotica) is unique: ‘A few days before the onset of the rains, Acacia trees start flowering. They also become very green’
Acacia nilotica is very variable in stature but is usually a multi-stemmed shrub. It has prominent long, paired straight thorns. (Today the taxonomists say anything that looks like an Acacia but doesn’t have thorns is not an acacia, and is probably an Albizia.) Acacia nilotica flowers mainly in the short rains, producing the fuzz balls characteristic of it’s sub-family. This species has sickly-sweet scented bright yellow flowers. The pods are sometimes curved, fleshy and hairy when young but become black when mature and release a sweet smell when crushed. The pods do not split along their length; instead they break up on the ground.
The timber is dark brown and very hard. It is great for tool handles. Formerly the pods were widely used to tan leather. Leaf extracts are used to treat a variety of medical complaints.
The Resilience Project now has a representative exploring Acacias in Kenya in preparation for work in the High Plains of Texas beginning in late October. Texas has a large number of Acacia–as many as 18 species. Some members of the genus are excellent small trees and shrubs for landscaping . As the water supply in the High Plains continues to diminish, we ought to think more about acacias.
Acacias are some of the most drought-tolerant bushes and trees one can grow. Once established, they need no water or fertilizer except what Mother Nature provides. Even during historic droughts, the acacias survive just fine.
An acacia known and loved in Central and South Texas is huisache (Acacia farnesiana or A. smallii), also known as sweet acacia. This spiny acacia usually it gets no more than about 15-20 feet high. During early spring, the branches are densely packed with half-inch spheres of bright-golden-yellow blossoms
Some of the prettiest early-spring sights in northeastern Mexico are broad valleys covered in huisache trees. On February mornings, the whole landscape glows golden yellow as far as the eye can see.
Reportedly, “huisache” comes from an Aztec word, huitz-axin. “Huitz” means she comes, and “axin” is a yellow oily substance derived from a bug and used to stain skin and other things yellow.
Some people consider it a trash tree. In South Texas it rapidly infests disturbed land and is consider a nuisance by many ranchers. However, on the eastern Edwards Plateau it seems much less likely to spread out of control. One gardener says: “We’ve had two small huisache trees in our yard for years. They grow slowly and have not multiplied.”
Another common acacia around College Station and Austin is Roemer’s acacia (A. roemeriana), sometimes mistakenly called catclaw. This multi-branched shrub or small tree has doubly compound leaves with 4-8 pairs of leaflets. In late spring it puts on round, fluffy clusters of white flowers. The curved catclaw-like thorns will get your attention if you brush against this shrub.
The true Catclaw acacia is a cold-hardy Acacia and grows 25 or 30 feet high. It has twice-compound leaves 1-2 inches long. Leaflets number 2-6 pairs. Instead of the bloom head being spherical as in Roemer’s acacia, flowers are cylindrical spikes of many tiny white flowers. This is the most cold-hardy acacia native to Texas and we hope to find it in the High Plains.
There also exists a Texas acacia which can be used as a groundcover. Fern acacia (A. angustissima) is a low-growing shrub with delicate, fern-like foliage. Its leaflets close together at night and when touched. Unlike most other acacias, fern acacia is thornless. White round flowers appear from time to time during the summer and fall. It is hardy in full sun or partial shade, and it never needs watering.
Acacia salicina is another thornless species of Acacia tree and native to Australia. Common names include Cooba, Willow Wattle, and Black Wattle. It is a large shrub or small evergreen tree growing 3 to 20 m tall. It has a life span of about 10–15 years. In the Northern Hemisphere, Acacia salicina flowers primarily from October to January and the seed pods are often visible from April to July. The tree’s seeds are shiny, black and have a crimson appendage-like aril.
The tree’s foliage and seed pods are important fodder for livestock during dry periods, since the tree can withstand pretty severe droughts. Its foliage and pods due compare poorly to other fodders in digestibility by livestock. But when drought hits, animals love it.
The wood is very hard and it is used in making fine furniture. At one time, the tree’s wood was used in the manufacture of axles for wagon wheels. Acacia salicina’s wood burns nicely and makes good fuel. The tree produces seed and timber for woodworking in as little as five years after planting.
The bark has been traditionally put to use by indigenous Australians as a toxin for fishing. The leaves of A. salicina are thought to be psychoactive, since indigenous Australians burn its leaves and smoke the ash to obtain a state of inebriation.
It’s great fun to be in Africa exploring the Acacias once again. My first trip to Kenya was in 1991 to work with ICRAF on a project sponsored by Michigan State University. Thanks to Catholic Relief Services I’m back in Kenya again to get refreshed and re-motivated to stoke the Acacia movement in the High Plains of Texas and anywhere drought is imminent in the US. After our August visit to drought-stricken Maine, anywhere may be fair game for Acacia.
For more in-depth studies:
Source of quote: ‘A few days before the onset of the rains, Acacia trees start flowering. They also become very green’. Kagunyu et al., 2016. The use of indigenous climate forecasting methods by the pastoralists of Northern Kenya. Pastoralism 6:7.
https://link.springer.com/article/10.1186/s13570-016-0054-0 or https://pastoralismjournal.springeropen.com/articles/10.1186/s13570-016-0054-0