A new carnivorous plant lineage (Triantha) with a unique sticky-inflorescence trap – pnas.org

Significance

Since Darwin’s ground-breaking monograph on carnivorous plants, scientists have recognized only 11 independent origins of plant carnivory. We report the discovery of a new lineage of carnivorous plants, represented by the North American flowering plant Triantha occidentalis. Among monocots, Triantha represents the only instance of a sticky-trap mechanism and a clearly documented case of holocarnivory, marked by enzymatic secretion consistent with prey digestion. Its trap is unique among carnivorous plants and, unexpected based on theory, in placing all of its prey-capture sites next to its insect-pollinated flowers. Given the existence of Triantha in close proximity to major urban centers on the Pacific coast, our study serves as a vivid reminder that other cryptic carnivores may yet remain to be discovered.

Abstract

Carnivorous plants consume animals for mineral nutrients that enhance growth and reproduction in nutrient-poor environments. Here, we report that Triantha occidentalis (Tofieldiaceae) represents a previously overlooked carnivorous lineage that captures insects on sticky inflorescences. Field experiments, isotopic data, and mixing models demonstrate significant N transfer from prey to Triantha, with an estimated 64% of leaf N obtained from prey capture in previous years, comparable to levels inferred for the cooccurring round-leaved sundew, a recognized carnivore. N obtained via carnivory is exported from the inflorescence and developing fruits and may ultimately be transferred to next year’s leaves. Glandular hairs on flowering stems secrete phosphatase, as seen in all carnivorous plants that directly digest prey. Triantha is unique among carnivorous plants in capturing prey solely with sticky traps adjacent to its flowers, contrary to theory. However, its glandular hairs capture only small insects, unlike the large bees and butterflies that act as pollinators, which may minimize the conflict between carnivory and pollination.

Footnotes

  • Author contributions: Q.L. and S.W.G. designed research; Q.L. performed research; C.A. contributed new reagents/analytic tools; Q.L., C.A., T.J.G., and S.W.G. analyzed data; and Q.L., C.A., T.J.G., and S.W.G. wrote the paper.

  • The authors declare no competing interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2022724118/-/DCSupplemental.

Data Availability

All study data are included in the article and/or SI Appendix.

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