Excerpts from Jim Conrad's
Naturalist Newsletter

from the July 10, 2016 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán MÉXICO
SPURGECREEPER

Twining up through a thicket of dead, weather-bleached stem-remains of last season's beautiful roadside Sunflower Goldeneyes, along a narrow, gravel road to a local garbage dump, a homely little vine with leaves caught my eye, simply because it was something green amid a lot of grayness. You can see the situation below:

Spurgecreeper, DALECHAMPIA SCANDENS

One of its deeply three-lobed leaves is shown below:

Spurgecreeper, DALECHAMPIA SCANDENS, leaf

Its flower cluster was very unusual, with flowers mostly hidden inside two deeply lobed, leafy bracts a little paler green than the leaves, as shown below:

Spurgecreeper, DALECHAMPIA SCANDENS, bracts

While taking these pictures I was thinking that something I'd not seen in the Cucumber/Melon Family had turned up, though I couldn't recall any species in that family producing such bracts. Since I don't see so well, it wasn't until I got home and put the following picture on the computer screen that it became apparent that not only was this in some other family, but that the flowering structures were outright bizarre. Below, you can see what I mean:

Spurgecreeper, DALECHAMPIA SCANDENS, maturing ovaries

In this picture, notice the vertical, green, slender item atop the uppermost roundish thing. The slender thing is a style topped by an expanded stigma, so the roundish thing beneath it is an ovary. Notice that the ovary appears to be somewhat 3-lobed. The picture shows at least three ovaries, all subtended by slender calyx lobes equipped with stiff, white bristles. There's no hint of male flower structures in the picture. When you see a 3-lobed ovary with the style emerging where the lobes join, and the flowers are unisexual, you should automatically think of the big, widely occurring Spurge or Euphorbia Family.

In the world of flowers, certain species can bear several separate ovaries in a single flower, as appears to be the case here, but in those blossoms each ovary is not subtended by its own calyx or bracts, which each of these ovaries clearly is. I can't recall having ever seen anything like this. However, I did remember seeing pictures of a vining member of the Euphorbia Family enveloping its flowers with large bracts like this, so now that species finally had turned up.

It's DALECHAMPIA SCANDENS, sometimes in English known as Spurgecreeper, distributed from the southern US where it's sometimes weedy, southward through all the America tropics, plus, apparently, and surprisingly, also there are native populations in Africa.

There's plenty of scientific literature about the genus Dalechampia and its 100 or so species of twining vines, precisely because its flowering structure is so weird. Evolutionary biologists like to explain how things evolved to be the way they are, and this vine's "bibracteate inflorescences" have been hard to explain. It's more or less understood now to be a "terminal staminate pleiochasim juxtaposed to a 3-flowered pistillate cyme," as Grady and Barbara Webster at the University of California, Davis, describe it, but once such a kinky arrangement is recognized the question becomes, "What forces of evolution could account for such a curious thing?"

The ongoing attempt to explain it all has come up with some unexpected insights that, of course, just lead to more questions. For example, our local Spurgecreeper species has been shown to comprise two or maybe three or even more "cryptic species" -- cryptic species being populations in which it looks like all the individuals are of the same species, but then it's found that certain groups within the species don't interbreed with one or more other groups -- another. And, by definition, populations that don't interbreed with one another are considered different species. They're "hidden species," cryptic.

With our local Spurgecreeper species the mystery is even greater because sometimes the different cryptic species live in the same place, and even share the same pollinators, which are bees. How do the genetically isolated populations stay genetically isolated? Researchers in the field try to figure it out.

A further curiosity is that though each cluster of flowers on each Spurgecreeper vine bear both unisexual male and female flowers, and regular pollination definitely takes place, sometimes Spurgecreeper closes its bracts over its flowers, keeping out pollinators, and pollinates itself -- a process that seems to kick sand in the face of sexuality itself. Why have sex, Surgecreepers seem to be asking, when you can impregnate yourself exactly when you're ready?

Who would have thought that such an humble little vine might live such an iconoclastic existence? I'll be keeping my eye on this vine, hoping to find some male flowers, and maybe see other features of its strangeness.