Steamy. Warm philodendron blooms lure pollinators.

Philodendrons Like It Hot and Heavy

SYDNEY, AUSTRALIA--Philodendrons may look like leafy dullards, but their image conceals a racy secret: hot sex. The reproductive antics of the tree philodendron, Philodendron selloum, generates heat that apparently serves to attract and reward pollinating beetles, who bask in its warmth. Now researchers have discovered that this warm glow is made possible by a finely honed system for rapidly getting oxygen to heat-producing cells.

Biologist Roger Seymour, of the University of Adelaide in Australia, had shown previously that P. selloum and a distant relative, the sacred lotus, regulate the temperature of their blossoms during flowering. They can keep their blooms warmed to about a balmy 35°C, regardless of the ambient air temperature.

Seymour's new work offers the first explanation of how P. selloum manages to get oxygen into the flower without the lungs and circulation system available to hot-blooded mammals. In an upcoming issue of the Journal of Experimental Botany, Seymour reports that it all begins when the plant "breathes" in large amounts of oxygen through stomata, or pores, in its flowers. When ambient temperature drops, the flowers cool slightly, triggering a heat-producing "breath." The oxygen diffuses through the stomata and eventually makes its way to mitochondria, power packs located inside the cells of the flowers, where it is used in the oxidation of lipids to release heat energy.

A key factor in a plant's "breathing" is the density of the stomata. Seymour found that each tiny flower, called a floret, has an average of 168 stomata, 1/20 the number in a leaf. "The airways are matched precisely to supply oxygen to the center of the floret and no more," Seymour explains. More stomata would cause excessive heat loss through evaporation, he speculates, while fewer would not let in enough oxygen for heat production.

"I think it's amazing that a plant can sustain the sort of metabolic [activity] that we expect of some mammals and birds," says Philip Withers, an expert in animal heat production at the University of Western Australia in Perth. Adds Seymour: "They do everything that animals do, except get up and walk ... for now."

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