|from the March 28, 2010 Newsletter issued from
Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO
BULL-HORN ACACIA & ITS ANTS
On a forest trail I almost stepped on something that would have lamed me if I'd been barefooted. It was a twig section from the tree above me, the tree shown above. This is one of a couple of Bull-Horn Acacias we have here, probably ACACIA COLLINSII, Subín in Maya, now in the dry season nearly completely leafless. A close-up of some thorns shows what's bull-hornish about them below:
In that picture notice that two of the 2-¾ inch (4 cm) spines bear holes near their tips. Ants chew these holes, enter the hollow thorns and live inside. A single ant colony may span several A. collinsii trees. If a herbivore comes along and touches the tree, the ants rush onto the animal and bite. Thus it's a mutualistic relationship, with both tree and ant benefiting.
The tree not only provides handy shelters for the ants but also feeds them. Take a look at the expanding leaf below:
Acacia leaves are bipinnate -- twice compound -- so the entire feathery, purplish, ant-mounted structure in the picture's lower right corner is a leaf about to expand. At the top, left of the leaf the shoehorn-like thing with two green-doughnut-like items in the horn is the leaf's stem, or petiole, and the green doughnuts within petiole's concavity are glands producing sweet, energy-rich nectar the ants feed on. Notice that many but not all the leaves' ultimate leaflets bear teardrop-shaped, dark purple, shiny things. Those are Beltian bodies, which are protein- rich structures eaten by the ants as well. Once the leaves are fully expanded, the Beltian bodies will have been eaten and there won't be a sign left of them.
The Bull's-Horn Acacia above me that day was practically leafless, but nearby grew a shoulder-high sapling. Saplings often bear leaves even when larger trees of their species don't. You can see a couple of the Bull-Horn Acacia's feathery, bipinnate leaves below:
from the April 3, 2011 Newsletter issued from Hacienda
Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO
|At least two closely related species of Bullhorn Acacia occur in the central Yucatán.
Earlier I decided that our local species was probably was Acacia collinsii, but
there was always a little doubt about whether it might be Acacia cornigera. The
only difference I can find mention of is that the fruits, or legumes, of A collinsii
split open when mature, while those of A cornigera don't.
While photographing the above flowers it occurred to me to look for old fruits in the leaf litter below the trees. After a lengthy search I found what's shown below:
That's a woody, split-open legume with its seeds, or beans, long gone. Therefore, now it's almost certain that our local plants really are Acacia collinsii.