Visitors to the Franklin Park Zoo gaze at the flower in a temporary greenhouse set up near the zoo’s entrance.
Visitors to the Franklin Park Zoo gaze at the flower in a temporary greenhouse set up near the zoo’s entrance.
Yoon S. Byun / Globe Staff

Rising from the moist soil like an alien pod, a rare plant affectionately known as Morticia is giving many Franklin Park Zoo visitors reason to hold their breath this weekend.

If estimates hold true, the horticultural gawkers may soon be holding their noses, too.

Since Friday, the 4-foot-6-inch amorphophallus titanum, known as the corpse flower, has been on the precipice of blooming, which occurs once every 5 to 15 years.

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When it finally unfurls, the flower will emit an odor of rotting flesh, an evolutionary advantage that draws flies, beetles, and other pollinators that help it reproduce. The flower could be a large as 5 feet wide.

“I’m excited,” said Mitch Rosenfield, 40, of Roslindale, one of about 250 people who toured a tiny, temporary greenhouse set up near the zoo’s entrance. “The suspense is killing me.”

Weighing in at 200 pounds, the massive potted specimen is one of four at the zoo that were donated by a New Hampshire doctor, but is the only one in a flowering phase.

Zoo staff estimate that since Friday 3,700 people have pushed through the plastic curtains into the greenhouse, which is kept around 82 degrees, to view the plant, a native of Indonesia.

In a nod to plant geeks and the horticulturally curious, the zoo opened early Sunday and offered free admission. In a little more than an hour, dozens of cameras snapped, fingers pointed, and children’s mouths hung agape at the plant’s slow lurch toward reproduction.

Through a large mirror above the plant’s mammouth center, a slight corona of deep lavender has appeared, a sign of things to come. A sheath of protective leaves has begun to fall away, exposing the massive, striated underside of the petals, called spathe, that cling to the oblong, vertical core, known as the spadix.

To Anna Cynar, 26, a science teacher in the Fitchburg schools, the true wonder was that such a low-intensity spectacle would draw so much interest.

“It’s nice to see faith in the natural world, that people would leave their homes and their computers to see a plant bloom,” Cynar said.