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Excerpts from Jim Conrad's
Naturalist Newsletter
Entry from notes taken during a camping trip on April 1, 2019 in El Seibal Archaeological Park in northern Guatemala's Petén department; tropical rainforest, elevation ~220m (~720 ft), ~N16.492°, W90.209°
SANDMAT ON A MAYA RUIN
Last April 1 in northern Guatemala's El Seibal Archaeological Park, a little forest trail entered a large plaza in the center of which stood a reconstructed ruin of an ancient Maya altar, as shown below:
At midday the heat was overwhelming, so I climbed the ruin's steps looking for shade. The ruin's stones were so hot that my feet burned through my shoes. And yet, when I sat down, right in front of me was a little plant that seemed to be thriving, rooted in a narrow crack in the stone. A hotter, drier environment hardly could be imagined. The plant's general form and flower structure were very familiar, being typical of the herbaceous, mat-forming kind of the genus Euphorbia, as shown below:
However, the genus Euphorbia is one of the largest of all genera, so what was the exact species of this one? Some euphorbias are treelike, others bushy, so this one being of the herbaceous, mat-forming kind by itself narrowed the choices down quite a bit. In the past, this group was designated as the genus Chamaesyce, but now that genus has been lumped into Euphorbia. An important feature distinguishing this mat-forming Euphorbia species from others is highlighted below:
The feature to notice is that the yellowish-green flower clusters grow at branch tips, not from leaf axils along the stems, as with most in this group. Other important fieldmarks are shown below:
The plant's vegetative parts are heavily covered with stiff hairs. The flower cluster's rounded top and the thick, yellowish green stems holding the pinkish cyathia (the special kind of flower structure of the genus Euphorbia firm up the ID.
This amazingly tough little plant is EUPHORBIA OPHTHALMICA, distributed in warm and hot environments throughout the Americas, including the southern US. The online Flora of North America gives its English name as Florida Hammock Sandmat, but Florida constitutes such a tiny part of its distribution, and the species occupies so many kinds of habitats between Florida hammocks and sun-stunned Maya ruins, that that name just won't do. We'll just call it Sandmat. Euphorbia ophthalmica has become an invasive weed throughout much of the Old World, too.
The species name ophthalmica surely indicates a traditional use of the plant for eye diseases, because very often plants that bleed white latex, as euphorbia species do, traditionally are used for that purpose. That's because of the Doctrine of Signatures, the belief that plants display special signs revealing to humans how to use them, and the euphorbias' white latex is similar to the whiteness of certain diseased eyes. However, white euphorbia latex often contains powerful alkaloids that can blind an eye, so in this case the Doctrine of Signatures is especially dangerous.
This particular sandmat is fairly common, often turning up in sidewalk cracks along city streets. In fact, two or three other sandmat species may occur with it, sometimes in the same crack. Once you get the fieldmarks of Euphorbia ophthalmica in mind, you might enjoy looking for other sandmat species in your area.