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from the June 14, 2015 Newsletter issued from Río Lagartos, on the Yucatan Peninsula's northern coast (~N21.60°, ~W88.16°), Yucatán state, MÉXICO
GLOBULAR ACACIA
On very thin soil atop limestone in the transition zone between savanna and mangrove nowadays there's a scrubby, super-spiny, feathery-leafed, small tree that even at a distance looks like it could be nothing other than an acacia. Usually its branches mingle with those of similarly gnarly, similarly spiny neighboring trees, but one individual about belly high grew in a savanna/cow-pasture producing the amazingly wide, flat-topped form shown below:

Up close it's the big, white, broad-based spines that get your attention, as you can see at the top of this page. In that photo, something else to notice is that the flowers are orangish-yellow and that they occur in unusually small, spherical heads. The twice-compound leaves also are strikingly small. Below, you can see how small the heads are in a picture with my finger in the background for scale:

Its one of the "ant acacias," an acacia that does what it can to make ants feel at home, probably so ants will rush out and bite anything thinking about nibbling the leaves. A close-up of a leaf with numerous pinnae and four dimpled, nectar-producing glands on its petiole, with an ant supping at the lowest gland, is shown below:

Another shot closer up showing an intently feeding ant and sharp stipular spines at a petiole base appears below:

Last season's brown, dried-up legume husks remain on the tree, tightly curled into such unkempt-looking clusters that you wonder why the tree keeps them, shown below:

The tree's well armored, splotchy trunk is shown below:

So many acacia species exist -- ten taxa listed for the Yucatan Peninsula -- that identifying them can be tricky. Luckily I know an Acacia expert in Germany, Dr. Wolf-Achim Roland, who seems happy to look at acacia pictures, so I just sent our pictures off to him.

Of course it's dangerous to identify things just from pictures, but Dr. Wolf figures we probably have Globular Acacia, VACHELLIA [ACACIA] GLOBULIFERA, which he calls Vachellia globulifera, because he's one of those who believe in splitting up the noble, old, huge and well-known genus Acacia into hard-to-remember genera like Vachellia. For years I continued to use Acacia, but eventually had to yield.

Anyway, Vachellia globulifera sometimes is known as the Globular Acacia, and it occurs from southern Mexico to Honduras.

Acacias are members of the Legume Family, and as such possess mycorrhiza on their roots that fix atmospheric nitrogen so that other living things can use it. Bees were buzzing the flowers as I photographed, and the soil in that area was so thin atop the limestone that all plants provided a great service just by being there, holding what little soil there was in place, photosynthesizing and producing cool shade instead of yielding their spots to naked, lifeless, hot rock.