Newly recognised carnivorous plant Triantha occidentalis

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When picking roses, one has to be careful with the prickles on the plant. Well, some small insects have to be extra careful when approaching the flowers of Triantha occidentalis, for it might trap them between trichomes and use them as diet supplements.

The species T. occidentalis, found in western North America, from California to Alaska, belongs to the Tofieldiaceae, in the order Alismatales. From July to September, when it blooms, the flowering stem does more than just hold a cluster of flowers higher up.

Researchers had observed that herbaria specimens of T. occidentalis often have tiny insects fixed to its peduncle, thanks to a sticky substance secreted by the plant, but hadn’t made too much of it until recently.

In 2016, a phylogenetic study reported that, just like some known carnivorous plants, T. occidentalis lacks genes involved in the NADH dehydrogenase complex, making researchers suspect of its love for insects. Because of this, Qianshi Lin from the University of British Columbia (UBC) and colleagues from UBC and the University of Wisconsin-Madison decided to investigate its apparent carnivory.

In their recent publication in the Proceedings of the National Academy of Sciences, the authors report that T. occidentalis is indeed a carnivorous plant. Isotopic analyses of its stems, leaves and fruits revealed that plants had absorbed and transported nitrogen-15 from fruit flies trapped by the plant that were enriched with the isotope. In addition, trichome exudates on the plants’ floral stems were found to contain phosphatase, an enzyme that is characteristic of carnivorous plants that don’t rely on other organisms for prey digestion.

While there are various mechanisms of botanical carnivory, for a plant to be considered truly carnivorous, it needs to be adapted for baiting, trapping, or breaking down its prey and being able to absorb nutrients from it. The presence of phosphatase in T. occidentalis, and the evidence that nitrogen from flies reached different parts of the plant, validate T. occidentalis recognition as a carnivorous plant.

The ability to absorb nutrients from their prey implies an advantage for the plant in terms of growth or reproduction. In T. occidentalis, “most or all of the N temporarily stored in the stem and fruit tissue migrates to the roots/rhizome, the only available storage sites for carryover to next year’s growth,” Lin and his colleagues write, making them conclude that “64% of Triantha foliar N comes from carnivory in preceding years.”

These findings are significant at different scales. In the broad plant grouping known as Monocotiledoneae, carnivorous plants were only recognized within order Poales. Now the order and family to which T. occidentalis belongs add to the list of plant lineages where carnivory has been confirmed.

The discovery of T. occidentalis carnivory not only reflects that carnivore traits can evolve independently on different plant lineages. It also shows, as the authors note, that “much is still to be learned about the ecology of individual plant species, even in relatively well-known floras.”

RESEARCH PAPER:

A new carnivorous plant lineage (Triantha) with a unique sticky-inflorescence trap Qianshi Lin, Cécile Ané, Thomas J. Givnish, Sean W. Graham Proceedings of the National Academy of Sciences Aug 2021, 118 (33) e2022724118; DOI: 10.1073/pnas.2022724118

Patrick Gibson graduated Cum Laude with a bachelor of science in biological sciences from Arkansas State University Campus Querétaro. He is interested in the different facets of botany and is happy to share his fascination for plants and science with others. Follow him on Twitter @pgibsonc.

Spanish translation by Lorena Villanueva Almanza