MELBOURNE, Australia — In the monsoon tropics of northern Australia, a little plant with prickles, gray-green leaves and purple flowers sprouted. It did not have a name, and it confounded scientists: Every time they encountered the plant, the sex of its flowers had changed.

It is not unusual for plants to be hermaphrodites — that is, for their flowers to have both male and female reproductive functions — but this species, a bush tomato whose fertilized purple flowers produce cream-color fruits, did not conform even to the fluid norms of the plant kingdom.

“This has me puzzled,” Peter Latz, a botanist from central Australia, wrote after a 1974 field trip in which he encountered the plant.

On Tuesday, some of the mysteries about this enigmatic species were revealed in a study published in the open access journal PhytoKeys. The researchers, from Australia and the United States, say they hope the work will shed light on the diversity of sexual expression in the plant kingdom, as well as challenging the notion of “normative” sexual conditions for other living things.