One three-ft-tall plant along the trail leading into the valley was almost the opposite of the rare, fragile, monotypic fern described above. It was the weedy Tropical Soda Apple, SOLANUM VIARUM, which is about as gangly and spiny as an herb can be. That's it below:
Many herbs bear spines, but it's unusual for big spines to arise from major leaf-veins as well as the rest of the body. In the woods near El Madroño I saw only three or four Soda Apples, but judging from what's happening in other places this is just the beginning of an invasion, now limited to appearing along trails but soon to extend onto slopes being logged because of dying trees.
This species is native to Brazil and Argentina but as a very unwelcome weed it's invaded many other tropical and subtropical areas, including the southern US. You can imagine how hard it is on a cow who chews into one of those leaves. You can visit a page showing fields invaded by Tropical Soda Apple in Georgia, plus people trying to root it out, and kill it by dousing it with a pathogenic species of bacterium at http://www.invasive.org/browse/subthumb.cfm?sub=2446&start=1.
Not only are Tropical Soda Apple's thorns dangerous to herbivores, but the the seeds can host several plant diseases such as Cucumber Mosaic Virus, Potato Leafroll Virus, Potato Virus Y, Tomato Mosaic, and a potato fungus. Each Tropical Soda Apple plant can produce more than 50,000 seeds. Fruits are eaten by livestock and wild animals, and a single cow patty can hold up to 150 seeds.
Yet, there are people who grow big fields of Tropical Soda Apple, on purpose. In fact, US Patent #20030226180 is for an efficient, large-scale process for growing this plant. Tropical Soda Apple is medicinal. In India it's grown commercially as a source for Solasodine, used by pharmaceutical companies as a starting material for the production of steroid compounds used for everything from contraceptives to arthritis and behavioral disorders.