Living in sand is not easy, and life – animal and vegetable - comes up with all kinds of wonderful solutions for doing so. Perhaps qualifying for one of the more bizarre adaptations is Pholisma sonorae, a perennial herb also known as sand food. It can be found in the sands of the Sonoran Desert, particularly in the Algodones Dunes. Sand food is unusual and bizarre in a number of ways: for a start, is a heterotoroph, lacking chlorphyll and looks for all the world like a dull grey powder-puff lying half-buried in the dunes sand. However, from April to June, it is covered in incongruously colourful flowers.
If the wind blows the sand away from around Pholisma sonorae, it takes on the appearance of a mushroom, with a long scaly stalk revealed. But this is only the beginning of the revelation – the stalk continues down as far as a couple of meters below the surface, eventually linking up with the roots of one of a number of different desert shrubs. For Pholisma sonorae is a parasite, depending for nutrients on the roots of its host. It does not, however, depend on its host for water – that it seems to deal with itself, absorbing water through stomata in its scale-like leaves; this independent skill means that sand food is not a parasite in the strict sense – its host does no appear to suffer from the attention of its guest.
And why sand food? The answer is simple: because Pholisma sonorae is remarkably clever at absorbing whatever water is available, its root is fleshy and edible, and it has long been a food source for the indigenous inhabitants of the Sonoran Desert.
[Header image, Photo credit: USFWS/Jim A. Bartel, Creative Commons License; other images http://www.calflora.net/recentfieldtrips/algodonesdunes08.html; for more details and images of sand food, see, for example, http://waynesword.palomar.edu/pholisma.htm, CalPhotos, Berkeley, and DCREP, California’s Desert Renewable Energy Conservation Plan.]