Researchers were also impressed by the lotus's sheer output of energy. A heating lotus flower can crank away at one watt, with 40 lotus blossoms churning out the same amount of heat as a living room light bulb. Seventy such flowers produce the heat of a human being at rest reading a newspaper.

''This is a lot of energy,'' said Dr. Todd Dawson, plant physiological ecologist at Cornell University. ''This is going to be expensive for a plant to do. It's burning up carbohydrate. So there's a cost involved here, and then the question is, what's the benefit?''

Researchers have begun to answer that question for a few of the thermogenic plants. When skunk cabbage blooms in early spring, its heat can melt away ice and snow around it, apparently protecting the flower from damaging cold. When the voodoo lily, another flower that can produce heat but does not regulate its temperature, heats up, its intensely putrid perfumes are more quickly turned to vapor and dispersed, helping to draw in pollinators. The effect is similar to that of putting a droplet of perfume on the warm human skin.

But why should a lotus flower keep on at a steady 85 to 96 degrees?

The authors of the new paper suggest that lotus flowers may be luring in heat-hungry pollinators, most likely beetles, with an attractively warm environment, providing an energetic reward for those that come to visit.

Dr. Bernd Heinrich, a physiological ecologist at the University of Vermont in Burlington, said such an environment might also be important for keeping beetles active in a flower during a cold night. An active beetle could rummage about and be fully coated in pollen by morning. In fact, a previous study found that beetles that lingered in lotus flowers and were trapped when the petals on these bowl-shaped blooms closed up for the night were indeed very active, spending the night mating and feeding.

Dr. Schultze-Motel suggests that the next morning these well-dusted beetles could quickly complete their job as pollinators. Rather than having to wait for the sun to warm them, the beetles, warmed by the flower, could take off to deposit pollen on the next lotus flower.

But Dr. Heinrich notes that warming may serve other purposes, including speeding flower development, and that there may be more than one explanation for the heat production.