NOW is the height of the fleeting season for desert truffles. (You didn't know?)

As soon as the first spring rains fall, the Bedouins who frequent the wide sand plains that commence just east of Damascus and stretch hundreds of miles to Baghdad begin scouring the ground for the telltale grasses and cracks indicating that truffles lie just beneath the surface.

They will tell you that the first sign of an auspicious year for the delicacy comes earlier. If lightning strikes in ferocious amounts during the first storms of November and December, the Bedouins say, the truffles will grow thick underground. If there is none, wait until next year.

"The thunder cracks the land, and then they appear," said Usama Calipha, who was plying desert truffles in carefully arranged one-foot-high pyramids in a downtown Damascus traffic circle for $10 a kilo (2.2 pounds). "It has something to do with the autumn rains, and it has something to do with God."

Desert truffles are a species of the mushroom family, and are distantly related to their more pungent, far more costly European cousins. Numerous varieties grow from Morocco to Saudi Arabia, but the desert of Syria and Iraq produces two main types, both known here by the Arabic name kamah.

There is a dark, reddish version, which is more dense and more prized than the slightly spongy white variety. Both resemble small round potatoes — some gnarled, some smooth — and the taste lies between the soft earthiness of a mushroom and the mealy chunkiness of an artichoke.

Desert truffles are packed with protein. Indeed, some aficionados compare them to tofu, in that truffles can serve as a meat substitute that both echoes and enhances the flavor of whatever they are cooked with.

Zeinab Osseiran Saidi, a hostess in Beirut, Lebanon, who likes to serve the truffles with meat and rice in a stew, searches for the least crinkled available. "Big or small doesn't matter; you want them smooth so you can just wash and peel them," she said.

The main hurdle in cooking truffles is the cleaning. As they expand, the truffles can embrace the sand in which they grow, so the more gnarled they are, the more likely they are to contain grit. Men scouring through baskets of the stuff in the Damascus wholesale fruit and vegetable bazaar also swear that truffles both soothe sore eyes and have a powerful aphrodisiac quality. "It makes you hotter," said Samir Rifai, a 28-year-old porter in the souk, adding quickly, "I mean for older guys."

Mostafa Abo el-Nil, a plant biologist at the Kuwait Institute for Scientific Research, who has studied the fleshy fungi, dismisses the Viagra-substitute idea. The lightning legend, though, appears to have some basis in fact.

The truffles spring from microscopic spores distributed just underneath the surface of the sand. (Cultivation has long proved elusive.) They grow into long, invisible threads, which attach themselves to the roots of squat rockrose bushes. Lightning triggers a chemical reaction that makes the accompanying rain rich in nitrogen compounds, which in turn seem to prompt the truffles to grow.

If there are no early thunderstorms, the truffles do not appear; indeed, sellers say five years can go by without any truffles. One Bedouin nickname for them translates as "the potatoes of thunder."

As they reach the size of golf balls, they begin to crack the surface of the sand, appearing as a field of bumps across the desert. Bedouin, knowing that they grow in tandem with rockroses, keep an eye out for those bushes before beginning their search for the unpredictable treasure. Big ones can be almost the size of a tennis ball. Those from Iraq have a reputation for being larger, but in recent years their cachet has fallen due to unverified suspicions that fallout from American weapons has contaminated them.

If the truffles are not dug up during the few weeks of winter rains, they pop up onto the surface and burst once the sand dries out, Mr. Abo el-Nil said, scattering millions of spores and starting the cycle again.