Researchers led by Thao Thanh Nguyen and colleagues at the University of Science, Vietnam National University Ho Chi Minh City, examined five natural varieties of Cosmos sulphureus collected in southern Vietnam. Their work, published in Plant Biosystems, combined three complementary lines of evidence: measurements of external morphological traits, microscopic examination of stem and leaf anatomy, and phytochemical analysis of the plants’ secondary metabolites. The varieties included single-flowered forms in yellow and orange, as well as semi-double forms in light yellow, yellow, and orange, allowing the team to ask whether the architectural distinction between single and semi-double flowers is echoed deeper inside the plant.

The short answer from the study is yes, and in a strikingly coordinated way. When the researchers subjected their morphological, anatomical, and chemical data to multivariate analysis, the five varieties separated into three groups, with the most important divide running between single-flowered and semi-double forms. In other words, a plant’s floral architecture predicted not just how its flower head is arranged, but also how its stem is reinforced and what kinds of defensive and medicinal compounds it accumulates. This kind of trait integration, where external form and internal physiology move together, is exactly what evolutionary biologists look for when trying to understand how complex phenotypes evolve as a package.

The anatomical differences were among the most vivid findings. Single-flowered varieties grew taller and showed clear signs of structural reinforcement: enlarged vascular tissues for transporting water and nutrients, and a continuous layer of sclerenchyma, the thick-walled support tissue, running through the stem. These are the hallmarks of a plant investing heavily in mechanical strength and hydraulic capacity, which makes sense for forms that channel resources into elongated growth and a simpler floral display. Lignin, the tough polymer that stiffens cell walls, was distributed more abundantly in these robust, single-flowered plants, giving their stems the internal scaffolding needed to hold up their height.

The semi-double varieties told the opposite story. These plants showed reduced lignification, meaning less investment in woody, structural tissue, but they compensated with markedly higher accumulation of secondary metabolites, the chemically diverse compounds plants use for defense, signaling, and interaction with their environment. In the Cosmos sulphureus varieties studied, this included elevated levels of phenolics, flavonoids, and alkaloids, three classes of compounds with well-documented antioxidant and pharmacological relevance. Phenolics and flavonoids in particular are the molecules behind much of the antioxidant activity attributed to plant extracts, and their enhanced presence in the semi-double forms points to a real phytochemical advantage.

Histological observation added an anatomical explanation for where these extra chemicals might be stored. The semi-double flowers contained a higher abundance of secretory structures, the specialized tissues and cells that plants use to produce, sequester, and release metabolites. This suggests that the enhanced chemical profile of the semi-double forms is not simply a matter of more chemistry per cell, but is supported by additional storage and secretory capacity built into the flower itself. The finding provides a satisfying mechanistic link: a change in floral architecture is accompanied by a change in the internal tissue landscape that accommodates a different metabolic strategy.

Among all the varieties examined, one stood out consistently. The orange semi-double type displayed the highest phytochemical levels across the tissues analyzed, making it the chemical champion of the group. For anyone interested in Cosmos sulphureus as a source of bioactive compounds, whether for pharmaceutical screening, nutraceutical development, or traditional medicine validation, this single variety emerges as the most promising starting material. The authors frame this as a practical outcome of the study: by linking floral form to chemical investment, breeders and researchers now have a visible, easily assessed trait, flower architecture, that can serve as a proxy for selecting germplasm with enhanced phytochemical potential.

Interpreted broadly, the study proposes a coordinated shift in resource allocation tied to floral modification. Plants cannot spend their finite carbon and energy budget twice; resources devoted to building thick, lignified stems are not available for synthesizing phenolic defenses, and vice versa. The single-flowered forms appear to prioritize the structural route, building taller plants with reinforced plumbing and support, while the semi-double forms redirect that investment toward secondary metabolism, filling their tissues with defensive and bioactive chemistry. This trade-off between structure and chemistry is a well-recognized theme in plant physiology, but demonstrating it so cleanly across naturally occurring varieties of a single medicinal species is a valuable contribution, because it shows the two strategies operating as alternatives within one species’ gene pool.

The findings also sit within a larger scientific conversation about how floral diversity evolves in the daisy family. Asteraceae is one of the largest flowering plant families, and its characteristic composite flower heads, which are actually inflorescences of many tiny florets, are famous for their developmental flexibility. Variations such as single versus double or semi-double forms arise from changes in how ray florets develop, and related research on chrysanthemums and other composites has shown that these architectural shifts can have deep developmental and genetic underpinnings. What the new Cosmos sulphureus study adds is evidence that such shifts ripple outward through the whole plant, influencing stem anatomy, lignin deposition, secretory tissue abundance, and metabolic profile simultaneously.

For a species with recognized medicinal value, the practical implications are considerable. Cosmos sulphureus has been documented as a source of antioxidant compounds, has been studied for its phytochemical screening and chromatographic profiles, and even serves as a bioindicator for bee diversity in agroecological research. If semi-double varieties reliably offer higher concentrations of phenolics, flavonoids, and alkaloids, then flower form becomes a low-tech selection marker that farmers, herbal producers, and plant breeders can use without expensive laboratory screening. At the same time, the study raises ecological questions worth pursuing: whether the chemical differences between floral forms affect pollinator attraction, herbivore pressure, or the plant’s performance as a nectar resource. By connecting what a flower looks like to what the whole plant is made of, this Vietnamese team has turned a familiar garden ornamental into a model for understanding how form, function, and chemistry are woven together in plants, and has given phytochemistry a surprisingly simple visual clue to follow.

Subject of Research: Floral polymorphism and its relationship to anatomy and secondary metabolism in Cosmos sulphureus

Article Title: Morpho-anatomical variation and secondary metabolism associated with floral polymorphism in Cosmos sulphureus Cav. (Asteraceae)

Article References: Nguyen, T. T., Nguyen, H. T., Nguyen, L. T., Nguyen, L. N., & Tran, T. T. (2026). Morpho-anatomical variation and secondary metabolism associated with floral polymorphism in Cosmos sulphureus Cav. (Asteraceae). Plant Biosystems, 160(5), Article 242. https://doi.org/10.1007/s44473-026-00248-9

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00248-9

Keywords: Cosmos sulphureus, floral polymorphism, plant anatomy, secondary metabolites, phenolics, flavonoids, alkaloids, lignin, Asteraceae, phytochemistry, Vietnam, medicinal plants

Mild steel is the workhorse metal of pipelines, automobiles, construction, and machinery because it is cheap, ductile, and strong, but its Achilles heel is corrosion. One of the standard industrial remedies is acid pickling, in which hydrochloric, sulfuric, or phosphoric acid strips rust and mineral scale from steel surfaces before further processing. The problem is that once the scale is gone, the acid keeps attacking the freshly exposed metal. Synthetic organic inhibitors can slow this secondary attack, but many are expensive, poorly biodegradable, and environmentally hazardous, which has pushed corrosion scientists toward so-called green inhibitors derived from plant extracts rich in nitrogen, oxygen, sulfur, and phosphorus-bearing phytochemicals capable of bonding to metal surfaces.

Cosmos sulphureus caught the team’s attention because prior phytochemical surveys had already catalogued a dense inventory of flavonols, anthocyanins, chalcones, and related phenolics in its tissues, molecules loaded with hydroxyl, carbonyl, and aromatic groups that are ideal electron donors for coordination with iron. The researchers collected matured aerial parts of the plant around the university gardens, shade-dried and ground them, and extracted roughly 5.56 grams of crude material from 300 grams of powder using a Soxhlet apparatus with 95 percent ethanol, yielding about 1.85 percent by weight. Fourier transform infrared spectroscopy then confirmed the presence of broad hydroxyl stretching near 3307 inverse centimeters, methylene bands at 2925, carbonyl absorptions around 1624, and ester, ether, and phenolic C-O stretches between roughly 1047 and 1268 inverse centimeters, precisely the functional architecture needed for metal binding.

The electrochemical evidence came from a standard three-electrode cell in which mild steel coupons of API X70 grade pipeline steel served as the working electrode in one molar hydrochloric acid at 298 kelvin. Electrochemical impedance spectroscopy, which measures how the metal-solution interface resists charge flow, showed a well-defined semicircular capacitive loop for the blank acid, signaling rapid metal dissolution. As the extract concentration rose from 200 to 1000 parts per million, the charge transfer resistance climbed while the double-layer capacitance fell from 6.55 x 10^-4 to 2.11 x 10^-4 microfarads per square centimeter, a classic signature of organic molecules displacing water and crowding the surface with an insulating barrier. Inhibition efficiency from impedance measurements reached 88.77 percent at the highest concentration, up from 76.93 percent at the lowest, confirming a concentration-dependent protective effect.

Potentiodynamic polarization, which sweeps the electrode potential and extrapolates the anodic and cathodic Tafel branches, delivered the headline number. The corrosion current density collapsed from 3.83 x 10^-4 to 2.77 x 10^-5 amperes per square centimeter in the presence of 1000 ppm of the extract, corresponding to 92.77 percent inhibition. Because the corrosion potential shifted by less than 85 millivolts relative to the blank, the extract qualifies as a mixed-type inhibitor, damping both the anodic dissolution of iron and the cathodic hydrogen evolution. Polarization resistance values rose steadily with inhibitor concentration, and when the temperature was raised to 308 kelvin, efficiency fell to 69.45 percent, indicating that the adsorbed film loosens with heat but remains appreciably stable. The team deliberately capped testing at 308 kelvin to avoid thermal degradation of fragile flavonoid glycosides such as rutin.

Scanning electron microscopy provided the visual proof. Polished steel coupons emerged smooth, coupons bathed in plain hydrochloric acid for eighteen hours came out rough and pitted, and coupons immersed in acid containing the extract retained a comparatively even surface. Together with the sharp drop in double-layer capacitance, which reflects the replacement of high-permittivity water at the interface by a lower-permittivity organic layer, the micrographs support the formation of a continuous protective film that physically bars aggressive chloride ions from reaching the metal.

To understand which of the weed’s countless phytochemicals actually do the work, the team turned to density functional theory calculations on five representative molecules reported in the literature for Cosmos sulphureus: cosmonidin, cosmonidin 4′-O-glucoside, chlorogenic acid, quercetin, and rutin. Geometry optimizations at the B3LYP/6-311G(d,p) level yielded frontier molecular orbital energies, electronegativities, hardness, softness, dipole moments, and the fraction of electrons transferred. High HOMO energies in cosmonidin, chlorogenic acid, and rutin point to facile electron donation, while high softness in cosmonidin 4′-O-glucoside and quercetin indicates molecules that deform easily to bond with the metal. All selected molecules showed a fraction of electrons transferred below 3.6, the threshold beyond which electron-donating ability ceases to correlate with inhibition efficiency, meaning each can feed electron density into iron’s vacant d-orbitals through coordinate bonds.

Local reactivity descriptors sharpened the picture further. Fukui indices and dual descriptors computed with UCA-FUKUI software identified the specific carbon and oxygen atoms most willing to surrender electrons, including particular positions in caffeic acid, chlorogenic acid, cosmonidin, quercetin, and rutin. Mulliken charge analysis flagged electron-rich oxygen atoms in the phenolic and carboxylic groups as the primary donor centers. Monte Carlo simulations in the Adsorption Locator module then placed each molecule over a cleaved Fe(110) surface surrounded by roughly 200 explicit water molecules, and the resulting adsorption energies for chlorogenic acid, cosmonidin, and rutin were consistent with chemisorption, the stronger and more durable of the two adsorption modes. Side views of the most stable configurations show the large planar molecules lying flat against the iron lattice, acting as steric barriers against the corrosive medium.

The proposed mechanism weaves these threads together. Chloride ions first displace water molecules and form an anionic underlayer on the steel, which electrostatically attracts protonated heteroatoms of the phytochemicals. Simultaneously, lone pairs on oxygen and the pi-electron clouds of aromatic rings donate into iron’s empty d-orbitals, anchoring a dense chemisorbed film that suppresses both anodic iron dissolution and cathodic hydrogen liberation. The authors conclude that Cosmos sulphureus extract is a competitive, natural, and sustainable inhibitor suitable for room-temperature acid pickling at around 1000 ppm, and they suggest that deeper experimental and theoretical work could push the efficiency further and pin down the molecular mechanism with even greater precision.

Subject of Research: Green corrosion inhibition of mild steel in hydrochloric acid using Cosmos sulphureus plant extract studied by electrochemistry and computational simulation

Article Title: Electrochemical and computational study of a weed based inhibitor for mild steel corrosion in an acidic medium

Article References: Kotupalli, M. R., & Pulapa, V. K. R. (2026). Electrochemical and computational study of a weed based inhibitor for mild steel corrosion in an acidic medium. Discover Electrochemistry, 3(1), Article 81. https://doi.org/10.1007/s44373-026-00168-5

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00168-5

Keywords: Cosmos sulphureus, green corrosion inhibitor, mild steel, hydrochloric acid, acid pickling, electrochemical impedance spectroscopy, potentiodynamic polarization, density functional theory, Monte Carlo simulation, Fukui indices, plant extract, chemisorption