Morphology of Solanum nectarifolium, a newly-described species of Australian bush tomato. Credit: Kym Brennan

A recent study led by Bucknell University Professor Chris Martine, biology, the David Burpee Professor of Plant Genetics and Research, has identified and described a new species of bush tomato with a special connection to ants—a taxonomic journey sparked by unusual specimens held in Australian herbarium collections.

The study, co-authored by a set of Australian botanists and Jason Cantley—the former Burpee Postdoctoral Fellow in Botany at Bucknell who is now Associate Professor of Biology at San Francisco State University—appears in PhytoKeys and underscores the critical role that natural history collections play in biodiversity science.

The new species, Solanum nectarifolium (Tanami bush tomato), was named for the location of its original collection area—the northern edge of the Tanami Desert—and for the uniquely conspicuous nectar-producing organs on the undersides of its leaves. These extrafloral nectaries exude a sweet liquid to attract ants that might protect the plant from herbivores. This remarkable trait marks the first known Solanum species with extrafloral nectaries visible to the naked eye, a feature previously observed only microscopically in a handful of related Australian species.

Martine first had an inkling that something was unusual about the plants from that region of the Northern Territory while working on a project with another former Burpee Postdoc, Angela McDonnell, now an Assistant Professor at St. Cloud State University. The pair included DNA extracted from two herbarium specimens representing Solanum ossicruentum, a species known as the blood bone tomato, that the Martine Lab described in the same journal in 2016, in an ongoing analysis meant to build a new bush tomato evolutionary tree.

Immature fruit and fruiting calyx of Solanum nectarifolium. Credit: Kym Brennan

Investigating unusual herbarium specimens

"We couldn’t understand why the two collections of the same species kept showing up in different parts of the tree," says Martine. "I had collected one of them and was certain that it represented Solanum ossicruentum, so I reached out to the person who collected the other one, David Albrecht, and asked whether he thought the plants he saw in 1996 at a place called Jellabra Rockhole could be something else."

Albrecht, Senior Botanist at the Northern Territory Herbarium at Alice Springs, suggested that the best way to know would be for botanists to revisit that remote region of the northwestern Tanami Desert and see for themselves. Martine, who had participated in seven collecting expeditions to northern Australia since 2004, wasn’t disappointed.

"I was kind of hoping he’d tell me that," Martine says. "Because I was already planning some new fieldwork in the Northern Territory and this would give me a great season to visit an area I had never been to before. But to really be prepared for a trip like that, I first needed to understand what other botanists had recorded and collected there in the past—and there is only one surefire way to do that: check what is in the herbarium collections."

So Martine started by using the Australasian Virtual Herbarium (AVH), a database of every plant specimen held in every herbarium in Australia. He searched for collections made of Solanum ossicruentum and a similar species called Solanum dioicum in the northern Tanami, finding 15 records for specimens gathered as far back as 1971.

Extrafloral nectaries (EFNs) on the leaves of Solanum nectarifolium. Credit: Kym Brennan

Fieldwork and discovery in Australia

"It was a really interesting distribution of points on the map, too," Martine says. "These were far south of the other records for Solanum ossicruentum, with hundreds of miles of ‘empty’ country between the two clusters. I couldn’t wait to get to Australia to see what those Tanami plants looked like."

In May 2025, Martine headed to Australia to meet his team for the trip: Cantley and paper co-authors Kym Brennan, Aiden Webb, and Geoff Newton, all associated with the Northern Territory Herbarium at Palmerston. But, first, Martine made a stop at another plant collection in the southwestern city of Perth.

"The visit to the Western Australian Herbarium was my first chance to spend a bunch of time with some of the actual specimens that I had earmarked based on the data in AVH," Martine explains. "And what I saw there legitimately blew my mind."

Staminate flowers of Solanum nectarifolium. Credit: Kym Brennan

Every specimen looked similar to Solanum ossicruentum, except for a few subtle characteristics—and one thing that Martine had never seen in more than two decades of Outback botanizing.

"On the backs of the leaves, along the veins, were these visible round disks," Martine notes. "They were each around a half-millimeter wide, really obvious, and the only bush tomato specimens that had them—we’re talking hundreds and hundreds of collections—were the ones from the northern Tanami."

Extrafloral nectaries and ant interactions

Martine thought they could be extrafloral nectaries (EFNs), non-flower organs on a plant that exude sweet liquid, typically as a means to attract ants that might protect the plants from herbivores. These were known to exist in a few Australian bush tomatoes, but those are tiny and have only been confirmed with microscopes. EFNs that could be seen without magnification would be something truly novel.

A few days later, Martine was in the herbarium at Palmerston and found the same pattern: more visible disks and only on plants from that same geographic area. Then he noticed that the most recent collection, from 2021, had been made by Kym Brennan—a renowned field biologist with an expertise in photography who was preparing for their trip in the next room.

"I ran in there and asked whether he remembered anything unusual about that collection—and before I could finish my explanation for why, he was already showing me an incredible photo of the leaves of that same plant. They were positively oozing with shiny, round droplets of nectar, all from those disks on the veins."

Eight days and more than 1,000 kilometers of driving later, the team arrived near Brennan’s collection site 50 kilometers southwest of the community of Lajamanu, right along the edge of the unpaved Lajamanu Road.

"This was more or less the same place where others had collected it in the early 1970s, so we were cautiously optimistic that we’d not only find it there again, but that the plants would have the flowers and fruits on them that we needed to describe this as a new species," explains Martine. "But it’s a harsh environment and the abundance of bush tomatoes is often dependent on fire occurrence. Sometimes you get to a place and there is nothing but old gray stems. Other times there are more happy plants than you can count. In this case, it was the latter situation."

The team got to work taking notes, making measurements, and shooting photographs. Then Cantley called for Martine to come over to the plant he was examining. There were ants all over the leaf undersides, avidly moving from disk to disk and probing them for nectar. That confirmed the hypothesis.

The collaborators decided on the scientific name "nectarifolium"—which translates to "nectar leaf," for obvious reasons—and the English-language name Tanami bush tomato. Martine then contacted a few experts about the conspicuous nature of the EFNs and whether they had been seen anywhere else in the genus Solanum, a group of around 1,200 species that includes the tomato, potato, and eggplant.

"As far as we know, this is the first Solanum species to be described as having extrafloral nectaries that you can see with your naked eye. That’s a pretty cool finding—and it all started with the examination of specimens that have been waiting in herbaria for as long as a half-century for someone to come along and take a closer look."

Significance of herbarium collections

Bucknell’s own Wayne E. Manning Herbarium, which holds approximately 25,000 plant specimens, now includes new samples of the Tanami bush tomato. But the official holotype remains at the Northern Territory Herbarium in Palmerston—almost 10,000 miles away from Bucknell’s campus.

"The Manning Herbarium may be small, but every specimen is a snapshot of biodiversity," Martine says. "These collections allow us to study where species occur, how they’ve changed over time, and—in cases like this—even help discover new ones."

The publication of the new species comes amid broader concern over the fate of natural history collections, such as Duke University’s recently announced closure of its herbarium housing more than 800,000 specimens. Martine and his colleagues agree that such closures could hinder future discoveries and conservation efforts.

Martine, a leading expert on Australian bush tomatoes, was recently elected president of the Botanical Society of America. He will begin his term as president following the organization’s annual meeting in August 2026.

"It still doesn’t feel real and probably won’t until I start my term just after Botany 2026," Martine says. "But I promise to do my best because plants are awesome and so are botanists."

More information: Christopher T. Martine et al, A new dioecious bush tomato, Solanum nectarifolium (Solanaceae), from the northern Tanami Desert, Northern Territory, Australia, with reassessment of S. ossicruentum and a change in the circumscription of S. dioicum, PhytoKeys (2025). DOI: 10.3897/phytokeys.268.169893

Citation: New species of bush tomato with visible nectar glands discovered in the Australian outback (2026, January 5) retrieved 5 January 2026 from https://phys.org/news/2026-01-species-bush-tomato-visible-nectar.html

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