Excerpts from Jim Conrad's
Naturalist Newsletter

Oleander, NERIUM OLEANDER, fruits & leaves

from the March 16, 2014 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
OLEANDER WILD ON THE DRY FRIO

On the cobblestone floodplain of the Dry Frio River over a mile from any residence, a bushy tree turned up that was familiar, yet its glossy greenness seemed very out of place in that, winter-locked, isolated little valley. You can see it below:

Oleander, NERIUM OLEANDER, invasive in Texas

It's familiar because it's one of the most frequently planted ornamentals in the world's tropics and subtropics, so we've seen it often in Mexico, and it's out of place because surely no one planted it here on this isolated stretch of the Dry Frio. It's the Oleander, NERIUM OLEANDER, which has been so widely cultivated for such a long time that its native region is uncertain, though southwestern Asia has been suggested, as has the Mediterranean.

The above plant is adorned with brown, cigar-sized fruits currently splitting open to release fuzzy seeds, as shown at the top of this page. Technically, these fruits are known as follicles, a follicle being a dry fruit that splits open only along its front suture, and which is the product of a simple pistil. Notice that the follicles are vaguely like milkweed pods, which similarly split open to release seeds whose long hairs carry them on the wind. The similarity is accountable by the fact that, now that the Milkweed Family has been merged with the Dogbane Family, both milkweeds and Oleanders are members of the Dogbane Family, the Apocynaceae. However, hairs of milkweed seeds elegantly radiate from atop a slender stem atop the seed, umbrella-like, while hairs on Oleander seeds are more generalized, as you can see in a seed close-up below:

Oleander, NERIUM OLEANDER, seeds

While we're looking, the Oleander's leaves just by themselves are pretty enough, as shown below:

Oleander, NERIUM OLEANDER, leaves

Even close up the leaf veins' primary symmetry and ultimate reticulations are good to see, as seen below:

Oleander, NERIUM OLEANDER, leaf veins

If this were a normal bush, leaves on its lower branches would have been eaten off by deer, who grossly overpopulate this area. Deer avoid Oleander leaves because they are toxic. Texas A&M's "Plants of Texas Rangelands" Oleander page says that as few as ten to twenty medium-sized Oleander leaves can kill an adult horse. They are toxic to all animal species, the page asserts, and many livestock and pets are poisoned, usually because they eat Oleander clippings or dead leaves. Even dead leaves remain toxic, though they become palatable. Compost containing Oleander leaves has been incriminated in poisoning. 

For my part, I appreciate any pretty bush that can survive the drought, pollution and physical abuse that Oleander can. With global warming about to reconfigure the biosphere in many unforeseen ways, eventually people may be happy to have any plant around able to survive the daily weather.