Bush tomato defies binary gender norms

A gender-fluid Australian plant, a distant relative of the aubergine, has been formally identified, ending a 50-year mystery.

The plant, commonly known as the Dungowan bush tomato, has baffled scientists ever since the first examples were collected in the 1970s. The confusion arose in part because it was unclear whether the specimens represented a new species, or variants of already described ones.

Mostly, though, it was because the flowers of the plant refused to conform to what might be termed botanical gender norms: some appeared to be female, others male, and still others a combination of both. 

And that, report a team of US and Australian researchers led by Angela McDonnell from Bucknell University in Philadelphia, turns out to be because it was exactly the case. The Dungowan bush tomato is transsexual, and has now been formally named Solanum plastisexum as a result. 

“This name, for us, is not just a reflection of the diversity of sexual forms seen in this species,” McDonnell and colleagues write in the journal PhytoKeys. 

“It is also a recognition that this plant is a model for the sort of sexual fluidity that is present across the Plant Kingdom – where just about any sort of reproductive form one can imagine (within the constraints of plant development) is present.”

Co-author Chris Martine, also from Bucknell, led the genetic research that underpins the findings. He is an unashamed bush tomato specialist, and with colleagues recently described two other members of the genus, including Solanum watneyi, named in honour of Mark Watney, the central character in author Andy Weir’s hit science fiction novel The Martian.

He and his current fellow scientists are also not ashamed to see a metaphor in their discovery of a gender-fluid plant.

“In a way, S. plastisexum is not just a model for the diversity of sexual/reproductive form seen among plants – it is also evidence that attempts to recognise a ‘normative’ sexual condition among the planet’s living creatures is problematic,” they write.

“When considering the scope of life on Earth, the notion of a constant sexual binary consisting of two distinct and disconnected forms is, fundamentally, a fallacy.”