Acaciella angustissima (prairie acacia, white ball acacia, ocpatl, or palo de pulque[4]) is most recognized for its drought tolerance and its ability to be used as a green manure and ground covering. It is a perennial, deciduous, and belongs to the family Fabaceae (beans/legumes) and as it grows it starts as a shrub but eventually matures to a small tree. The tree has a high density of leaves along with small clumps of white flowers and creates 4–7 cm long seed pods.
Acaciella angustissima is found in tropical areas around the equator since, its water needs can vary from 750 to 2,500 mm a year. It has an advantage it can withstand a moderate drought, since its leaves are retained even in long dry periods. Aside from being drought tolerant, Acaciella angustissima also has the benefit of being a green manure, since it has such a high leaf density, but also loses the majority of its leaves each season. So the leaves can be used in composting or can be saved and used as livestock feed. It should only be used as an additive to the feed and not the main source, since it also toxic in high doses.
Description
Acaciella angustissima is normally a shrub but can also look like a small tree when fully grown, since its height can vary from 2–7 m depending on the growing conditions. Large clumps of small white flowers cover the branches of the bush. The flowers have 5 petals with a large number of stamens extended far past the petals.[5] The plant also produces a small seedpod that starts out green, but then turns brown when fully matured. The seedpods usually have a length of 4–7 cm, and are 6–8 mm wide. The leaves which are one of the plant's key traits are made up of 10–20 pairs of long thin leaves that go down a stem. They come in pairs of 3–12. One unique feature of the Acaciella angustissima is that it is thornless unlike most members of the genus Acacia[6] (which it formerly belonged to).
History
Acaciella angustissima comes from the plant family Fabaceae. It only grows in very wet parts of the world, usually around the equator due to its large consumption of water. It is native to southern parts of North America, the Caribbean and the majority of South America.[6] However, it is able to grow at almost any elevation and usually prefers a warm climate of 25–30 degrees Celsius. Acaciella angustissima is still one of the many crops under-utilized and researched. Luckily there is hope, roughly 20 years ago researches started evaluating it in tropical areas such as Zimbabwe.[5]
Natural habitat
Acaciella angustissima fruit (bean)
Altitude: 0-2600m Annual temperature mean: 5–30 deg. C. Annual rainfall mean: 895-2870mm Soil: A. angustissima is well-suited for acidic, low-nutrient soils and it has very good resistance to drought.[7]
Growing conditions
Since Acaciella angustissima is a shrub, it propagates (spreads) through its seeds or clippings.[6] The seeds come from all the pods that the Acaciella angustissima grows each year, and the clippings should be taken from a somewhat hard branch, to better support themselves when transplanted.[8]Acaciella angustissima should be planted in March or April in soil that has good drainage and is more on the acidic side on the pH scale.[9] To be most effectively utilized it should be used to prevent erosion, since it has such a large root system. This is also one of its downfalls, since when it is intercropped with other species its roots can be a major competitor for vital nutrients. Luckily its fallen leaves can provide enough N, K, and P to keep smaller nearby plants healthy, and provide some shade at the same time.[10]Acaciella angustissima is self-sustaining and does not need fertilizer, but has been found to respond well to fertilizer when added. However, the plant has a large water requirement. It requires a minimum "rain fall" of 700 mm but can handle up to a maximum of 3 000 mm.
Uses
Alcoholic beverages
The bark is used in the production of alcoholic beverages.[7] The root is used in the drink pulque in Mexico.[11]
Forage
The seeds of Acaciella angustissima are high in protein and are somewhat useful as forage for livestock.[12] The tree has a tannin content of 6%, which inhibits the ability of livestock to make use of the tree's protein.[7]
There are unfortunately many constraints holding Acaciella angustissima back from being adopted. Firstly the amount of water it needs to survive is 3 – 4 times the amount of rainfall found in more northern parts of Africa. This is unfortunate since dry land farmers could benefit the most from this tree. The second and most important constraint is that, Acaciella angustissima can actually act as a weed. It is so effective at propagation that it spreads rapidly.[10] Thirdly, Acaciella angustissima contains roughly 10% tannins, which is the plant's natural defense mechanism. The taste created by the tannins is not usually welcomed, and the compound itself negatively affects livestock digestive systems.[13]
Practical information
The most important fact about Acaciella angustissima is that it has turned into a weed in its native habitat, so it should only be used in a controlled environment or when absolutely necessary.[5] The only times it should be considered are when dealing with a harsh conditions where only weeds can survive, and some type of ground cover is needed to help with erosion control. If these circumstances are true, then the expected final height of the plant should be kept in mind when planting to prevent over crowding. Intercropping would also be complementary, by allowing farmers to take advantage of the unused space between plants, the nitrogen fixing habit, and the shade provided by the bushy branches.[10] Due to the complex structure of the leaves it can take a year for them to decompose and release nutrients into the soil. To create a seed bank, it is important to remove all the seeds from the pod, and then clean them before storing, so that the pod doesn't break down and start attracting insects.
