Same Species, Different Chemistry: Scientists Redefine What a Plant Chemotype Really Is

Two plants standing side by side in a meadow may look identical, carry the same Latin species name, and yet be chemically worlds apart. One may smell sharp and camphor-like, another sweet and resinous, and a third may be toxic where its neighbor is harmless. This hidden chemical diversity within a single plant species is the subject of a new study published in Trends in Plant Science by researchers at Bielefeld University, who argue that the scientific term used to describe it — the chemotype — has been applied so inconsistently that decades of research findings may be far less comparable than scientists have assumed. The team, led by Professor Dr. Caroline Müller, now proposes a systematic framework for defining chemotypes in a way that is precise, unambiguous, and reproducible across laboratories.

A chemotype, in principle, describes a group of plants within one species that share a characteristic chemical composition, setting them apart from other members of the same species. The compounds involved are typically the specialized metabolites that plants deploy as chemical weapons and signals: terpenoids, which give many herbs their volatile aromas, and alkaloids, which often carry potent pharmacological or toxic effects. These substances influence how a plant interacts with herbivores, pathogens, and pollinators, shaping its ecological success. Because the same species can produce markedly different blends of these compounds, two individuals may occupy subtly different ecological niches despite being genetically close enough to interbreed.

The core problem identified in the study is definitional drift. Until recently, Müller explains, plants of the same species were routinely assigned to different chemotypes without specifying precisely which organ of the plant was analyzed and which chemical family was being compared. That omission matters enormously, because chemical profiles are not uniform across a plant. Leaves, flowers, and roots can each carry distinct mixtures of metabolites, and a classification built on flower chemistry may contradict one built on leaf chemistry for the very same individual. Similarly, a plant that appears to belong to one chemotype when judged by its terpenes may fall into another when its alkaloids are measured.

To demonstrate just how consequential this ambiguity can be, the researchers turned to common tansy (Tanacetum vulgare), a widespread flowering plant whose terpene composition varies dramatically between individuals. Working within the DFG-funded Research Unit FOR 3000, the team showed that the assignment of a tansy plant to a particular chemotype depends strongly on which chemical family is examined. In their analyses, terpene profiles differed markedly between the flowers and leaves of plants belonging to three chemotypes, while the roots displayed more similar profiles across individuals. A single plant, in other words, can present different chemical identities depending on where and how one looks.

The proposed solution is a set of clear criteria: any chemotype designation should explicitly state which plant organ was sampled and which chemical compound class was used as the basis for classification. This systematic approach, Müller and her colleagues argue, establishes what exactly constitutes a chemotype and removes the interpretive latitude that has allowed the term to be stretched in different directions by different research groups. The method of research underlying the publication is a meta-analysis, meaning the authors synthesized and evaluated existing literature to expose the inconsistencies and formalize the new criteria.

The stakes extend well beyond taxonomy. Chemotypic differences are largely genetically determined, which means they are heritable and stable across generations, but environmental conditions can further modify the precise chemical composition a plant produces. Temperature, soil, light, and herbivore pressure can all nudge the metabolic output of an individual, layering environmentally induced variation on top of genetically fixed differences. Disentangling these two sources of variation is essential if researchers want to make reliable claims about why one population of a species smells different from another, or why one is more resistant to a particular pathogen.

Practical consequences follow directly. Tansy itself was historically used as a so-called worm herb to treat intestinal worms, yet depending on its chemotype the plant can vary considerably in toxicity — a serious concern for anyone relying on traditional remedies without chemical verification. Cannabis offers an even more prominent example: different chemotypes of the same species can differ substantially in their tetrahydrocannabinol (THC) content and, consequently, in their physiological and legal implications. In both cases, a chemotype label that is not anchored to a defined organ and compound class conveys far less information than users, clinicians, or regulators need.

Agriculture and plant protection stand to benefit as well. The chemical properties that define a chemotype influence how attractive a plant is to herbivores and pathogens, so knowledge of chemotypic variation could eventually help breeders and agronomists select plant lines more specifically and increase crop resilience to environmental stresses. Rather than treating a species as a chemically uniform entity, breeding programs could exploit the natural diversity within it, choosing chemotypes whose metabolite profiles confer resistance or reduce pest attraction. Müller emphasizes that a consistent way of describing chemotypes makes this diversity visible and provides a foundation for better understanding and using it in both research and practical applications.

The Bielefeld study also connects to a broader scientific shift toward recognizing individuality within species. Research at Bielefeld University addresses individual differences within plant species as part of the university’s strategic focus area InChangE — Individualization in Changing Environments — reflecting a growing awareness that population-level averages can conceal biologically meaningful variation. As climate change alters the environmental conditions that modulate plant chemistry, understanding how genetically determined chemotypes respond and shift becomes increasingly urgent for ecology, conservation, and food security alike.

What the study ultimately delivers is a call for rigor in a corner of botany where imprecision has quietly accumulated. By requiring researchers to name the organ and the chemical family behind every chemotype assignment, the new criteria promise findings that can be replicated, compared, and built upon across studies. For a field whose subject matter ranges from the fragrance of a meadow herb to the potency of medicinal cannabis, that clarity is not a formality — it is the difference between chemical diversity that can be systematically understood and used, and diversity that remains, however fragrant, scientifically opaque.

Subject of Research: Standardizing the definition of plant chemotypes based on organ-specific and compound-class-specific chemical variation

Article Title: Same plant species, different chemistry

Article References: Same plant species, different chemistry. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: chemotype, plant chemistry, Tanacetum vulgare, terpenoids, alkaloids, medicinal plants, agriculture, plant protection, THC, Bielefeld University, Trends in Plant Science, chemical ecology