At first glance, you might think the rounded mound sticking out of the sand was a mushroom cap. But look closer – those purple spots are flowers. It’s not a fungus, it’s a plant -- and as you might guess from the complete absence of green leaves, it’s a parasitic one.
Sandfood (Pholisma sonorae) lives in the sandy deserts of southern California and Arizona. It grows in loose sand near its hosts, which are typically small shrubby desert perennials like arrowweed, burro-weed, or dyebush. The relationship between host and parasite isn’t obvious when you walk by, because the two are attached at the roots.
A sandfood plant taps into its host’s root system and siphons off sugars and proteins to put toward its own growth. And can they ever grow – at the end of a growing season there can be a fleshy stem as long as a grown man hiding underneath that mushroomy flower. A full-grown sandfood can actually weigh more than its host plant, though a lot of that mass is water. P. sonorae doesn’t need a host for that part – it absorbs water through the modified scaly leaves covering its stem. And it’s possible that sandfood’s ability to store up fluid lets its hosts turn the tables on it during long droughts: sucking water out of the parasite to let them keep photosynthesizing in conditions that make other plants shut down their food factories. If that turns out to be true, it may be fair to ask which plant is actually the parasite. And the answer may be as changeable as the weather.
Photo © 2008 Michael L. Charters,
used with permission