National Geographic : 2013 Dec
136 national geographic • december 2013 both fire and herbicides, and yellow toadflax, which exudes a skin-burning chemical (a Homo sapien-icide) to fight off human pickers like me. The names we give these creatures are a testa- ment to humanity’s disgust: pigweed, dogbane, horseweed, sow thistle, stink grass, ragwort, poverty sumpweed. Programmed by evolution to eke out a living in the harshest regions of the planet, they find life anywhere else like retiring to Florida. Salsola, I would discover, is their Genghis Khan. An invader from the Eurasian steppes east of the Ural Mountains, Russian thistle has shown an appalling ability to thrive in its adopted land. Every winter the plants die, and the stems become brittle, breaking with a gust of wind. Then they go rolling and roll- ing, merging into masses of ugly, brown thorn clouds that can bury a house or feed the fury of range fires. Good for almost nothing, the biggest plants—they get as large as Volkswagen bugs—can scatter as many as 250,000 seeds along a path extending for miles. The seeds By George Johnson Photographs by Diane Cook and Len Jenshel T he trouble begins around sundown, when a couple of city slickers out for a drive in the desert become stranded along a lonely canyon road. It’s silent and windless. Yet one by one, like wolves in the night, tumbleweeds start gathering around them. “They’re following us,” the heroine cries. When her husband tries to intervene, one of the tumbleweeds leaps at his eyes. “It was just like an octopus!” he shouts, af- ter tearing it from his face. “There was living strength in it!...Where did all that energy come from? How can you animate a dead weed?” There were scarier moments in The Outer Limits, the old black-and-white science fiction series. But this episode, “Cry of Silence,” holds a special horror for me. My own encounter with these monsters be- gan one autumn when my wife and I decided to buy some land—a couple of acres for horses on the outskirts of Santa Fe. We had noticed a few brittle tumbleweed skeletons lying around. But that was to be expected. Salsola tragus, a s i t ’s properly called, or Russian thistle, has become ubiquitous in the West. A few months later, after purchasing the property, we found more: piles of tumbleweeds that had accumulated against a stand of piñon and juniper trees during the March winds. I tried not to worry. I had fought weeds of all kinds at our house in town, including the occa- sional tumbleweed. There was also kochia and flixweed, a wild mustard that seemed to resist Science writer George Johnson has lived in Santa Fe for 19 years. Diane Cook and Len Jenshel shot gardens at night for the March 2013 issue.