Oops. That mangrove tree's no lady.

The supposedly female trees of the white mangrove have turned out to be perfectly good hermaphrodites.

This raises the question of why in the world there are male white mangroves, say Carol L. Landry of the University of Michigan in Ann Arbor and her colleagues. They estimate that less than 1 percent of flowering plants have both hermaphroditic and male plants, a mating system called androdioecy. In the past few years, botanists have reported this odd sex mix in a Japanese ash tree as well as in a member of the cucumber family.

The presumed female flowers of the white mangrove, Laguncularia racemosa, sport what look like male parts, but botanists had assumed that these organs didn't work. Landry tested that assumption in Florida by covering these flowers with small bags to seal out pollen from other trees. About half of the bagged flowers still managed to produce fruit.

Landry experimented with other crosses and found that the hermaphroditic flowers set more fruit when fertilized with pollen from all-male trees than when they self-pollinated.

In a field test on San Salvador in the Bahamas, Beverly J. Rathcke, also of Michigan, and Lee B. Kass of Elmira (N.Y.) College also found functional hermaphrodites, as well as males.