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SOLVED: which Acacia is it ?

Biskra, Algeria

this Acacia grows in southern cities of Algeria, it is a thorny tree, evergreen, more than 4m high, Leaves are alternate, bipinately compound, a pair of white thorns, about 10cm long or more. identication of the acacia species is difficult in the absence of specialized flora. thanks for your aide

Thumbnail by gibinfo Thumbnail by gibinfo Thumbnail by gibinfo Thumbnail by gibinfo
Vienna, VA(Zone 7a)

The Acacia genus was divided, and one of the new genus names is Vachellia. Your tree could be Vachellia karroo, which is naturalized in North Africa.

Here is one link for V. karroo:

There are other sites but I had difficulty copying the best link.

Biskra, Algeria

Hi Muddy1, there is a great similarity between the leaves and thorns and even fruit, but the thorns of my Acacia are smaller, it would be of the environmental conditions!

Vienna, VA(Zone 7a)

It could be due to different environmental conditions, or it could be a different species altogether.

There were more than 1,300 species of Acacia before the genus Acacia was divided into 5 separate genera, one of which is Vachellia.
This article does a much better job of explaining it than I can, and also lists the other new genera if you want to do more research:

Good luck, and have fun!

Sodwana Bay KZN, South Africa

I agree that your tree is Vachellia (Acacia) karroo, definitely.
As per the "Guide to the Acacias of South Africa" by Nico Smit, Briza Publications 1999:

"On large, mature trees the spines can be short, while on younger plants and on new growth they may attain a length of 100 mm or more. In most cases they have a mean length of 40 mm."

The 25 cm long thorns in the link above is extremely far fetched!! And it definitely is not a weed in Souh Africa.

Regards, Maddy

This message was edited Nov 12, 2013 8:23 AM

Vienna, VA(Zone 7a)

Thanks for the input, Maddy! It's interesting that the thorns on young trees and new growth are longer than those on mature trees; I would have thought it to be the opposite.

Adelaide, Australia(Zone 10a)

Also, on large mature trees, the parts of the crown of the tree that are around the edges are thornier than the parts in the centre of the crown. It is a significant biological burden on the health of the tree to make so many thorns, rather than flowers for propagation and leaves for food production. Evolutionary processes have favoured the survival of the plants that only make thorns where they need them most, rather than all over the plant.

Elephants and Giraffe are the major browsers on African "Acacia" species - the tree only "needs" thorns until its leaves are above the head height of Giraffes and its main trunk and branches become too thick for the Elephants to break them down. Relatively few plants survive to reach this size - hence the classic African savannah with grassy plains and scattered trees. (Please note that I am simplifying madly here - many other things influence the density of trees as well, but I just wanted to mention the stuff about the thorns and why they grw where they grow.)

Sodwana Bay KZN, South Africa

But of course the thorns do not stop a giraffe (nor elephant) from browsing on Acacia, no matter how long they are...

This message was edited Nov 13, 2013 12:39 PM

Thumbnail by maddy
San Francisco, CA

Man, I hate it when giraffes get in my garden!

Adelaide, Australia(Zone 10a)

True maddy, what they do, though, is to make the Giraffe eat more slowly - this does allow the plant time to bring its other defenses "on-line".

There is a fairly good write up on the whole process here: . I think I first came across this in a nature documentary, but I can't remember which one. I find the complexity and fine-tuned nature of the whole system fascinating.

Vienna, VA(Zone 7a)

Thanks for the link, KK; I found it fascinating as well. So, Gibinfo was right: the thorns on his trees are shorter due to environmental conditions; i.e. few if any predators.

Biskra, Algeria

Hi,thanks to your help Muddy, I was able to finally know the species Acacia seyal, it has a great simillary with Acacia karoo, thank you even more

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