The genus has an ancestral basic chromosome number of x = 5, and three ploidy levels have been documented: diploids with 2n = 10 chromosomes found in all sections, tetraploids with 2n = 20 found only in section Paeonia, and mostly artificial hybrid triploids with 2n = 15 chromosomes. Peonies are unusually good subjects for karyomorphology, the study of chromosome form, because their chromosomes are large for flowering plants, measuring 10 to 15 micrometers in length compared with the much smaller chromosomes of most other angiosperms. This makes them an ideal model for practicing and teaching cytological techniques, which involve measuring the long and short arms of chromosomes in spread metaphase plates to characterize the physical structure of a chromosome complement.

Such approaches are simple, inexpensive and powerful sources of comparative information in systematic studies. The research emerged from a four-day course held in Pisa between February 6 and 9, 2024, organized by the Group for Floristics, Systematics and Evolution of the Italian Botanical Society. Participants analyzed permanent microscope slides prepared by one of the researchers roughly two decades earlier, between 2002 and 2005, as part of a study on Italian Paeonia species whose chromosome counts were only partially published at the time.

The slides had been made from root tips of plants cultivated in pots at the Botanical Garden of the University of Calabria, in Arcavacata di Rende, Cosenza. After hydrolysis in 1N hydrochloric acid at 60 degrees Celsius for seven and a half minutes, the tips were stained with leuco-basic fuchsine and squashed onto slides. In total, fourteen metaphase plates were analyzed by the course participants using the MATO software package.

The team focused on four quantitative traits. The first, total haploid chromosome length, serves as a proxy for genome size and is calculated by summing the lengths of all chromosomes in a plate and dividing by the ploidy level. The second, mean centromeric asymmetry, captures intrachromosomal asymmetry by measuring the average difference between the proportions of long and short chromosome arms.

The third and fourth, the coefficient of variation of chromosome length and the coefficient of variation of centromeric index, quantify interchromosomal asymmetry and heterogeneity in centromere position, respectively. The results were remarkably uniform. All four taxa displayed the expected tetraploid chromosome number of 2n = 4x = 20.

Total haploid chromosome lengths ranged from about 93 to 127 micrometers across plates, while values of the asymmetry indices fell within broadly overlapping ranges. Non-parametric Mann-Whitney pairwise tests revealed no significant differences among the four taxa for any of the karyomorphological parameters, and a principal component analysis, whose first two axes accounted for 85 percent of total variation, showed extensive overlap among all groups. One taxon offered a faint hint of divergence.

The two accessions of Paeonia mascula subsp. russoi showed slightly elevated values of chromosome length and centromeric index variation, which marginally separated them from the other taxa in the multivariate analysis. Intriguingly, this species is also considered taxonomically more distinct from P. officinalis and P. peregrina on the basis of leaf and root structure. However, the researchers caution that the very limited sampling prevents any firm conclusion, and the homogeneity observed across the sample remains the dominant signal.

To the authors' knowledge, this is the first quantitative study of karyotype asymmetry and structure in tetraploid European peonies, though the results agree with earlier qualitative observations from the 1980s and 2000s. The apparent homogeneity may extend even further: the coefficients of variation measured in the studied taxa closely resemble those reported for the tetraploid Paeonia mairei, a species endemic to China, suggesting that similar chromosome architecture could characterize large portions of section Paeonia worldwide. This uniformity also poses a methodological challenge.

Karyotype similarity can obscure the allotetraploid origin of these species, meaning their genomes may combine chromosome sets from different ancestral parents, a hypothesis advanced by earlier evolutionary studies. Traditional Feulgen staining approaches may simply be unable to reveal such hidden hybrid ancestry. The authors point to molecular cytogenetic techniques such as genomic in situ hybridization, which has proven effective in cultivated hybrid peony varieties, as a promising path forward for untangling the origins of wild tetraploid peonies and the evolutionary history written into their remarkably similar chromosomes.

Subject of Research: Karyotype asymmetry and structure of tetraploid European peonies (Paeonia sect. Paeonia)

Article Title: Tetraploid European paeonies ( Paeonia ) show a homogeneous karyotype asymmetry and structure

Article References: Peruzzi, L., Franzoni, J., Giacò, A., Abidi, E., Alù, E., Barone, G., Bianchi, E., Cataudella, C., Di Iorio, E., Guerrina, M., Mondello, F., Paino, L., Pentassuglia, M., Porrovecchio, M., Rivieccio, G., Siccardi, E., Stinca, A., Tei, A., Volanti, V., & Tiburtini, M. (2024). Tetraploid European paeonies (Paeonia) show a homogeneous karyotype asymmetry and structure. Italian Botanist, 18, 51-57. https://doi.org/10.3897/italianbotanist.18.135403

Image Credits: AI Generated

DOI: 10.3897/italianbotanist.18.135403

Keywords: Paeonia, peony, karyotype, cytotaxonomy, tetraploid, chromosomes, karyomorphology, PCA, Italian Botanical Society, genome size, allopolyploidy, European

The BBCH scale, developed originally by Germany’s Biologische Bundesanstalt, Bundessortenamt and chemical industry, provides a universal decimal coding system for describing plant development, from BBCH 000 (the dry seed) through BBCH 907 (a fully desiccated, dead plant). While the system has been applied to countless crops and to related chenopods such as quinoa and the Taiwanese supergrain djulis, no comprehensive framework had ever been established for C. album itself. That gap mattered, because the species occupies a peculiar dual position in agroecosystems: its young shoots deliver vitamins A, C and K, iron, calcium and protein to rural diets, while mature plants compete aggressively with wheat, mustard and barley, host plant pathogens and insect vectors, and replenish soil seed banks with tens of thousands of seeds per plant.

To build the framework, the research team, led by Reena Rathore and Dipti Bisarya of Lovely Professional University in Punjab, worked with two naturally occurring seasonal populations that differ not only in phenology but in chromosome number. The winter population, a hexaploid with 2n = 54 chromosomes, dominates Rabi crops in northern India between November and March and is characterized by broadly ovate leaves, a semi-dwarf stature and a short-day flowering response. The summer population, a tetraploid with 2n = 36 chromosomes, occupies wastelands and field margins from April to September, growing taller with lanceolate leaves and a long-day response. Ploidy levels were confirmed through chromosome counts of root tip meristems and floral buds, supplemented by measurements of stomatal size and density, and voucher specimens were deposited in the Botanical Survey of India herbarium.

Field trials were conducted at the university’s research farm in Phagwara, Punjab, in a subtropical climate with sandy loam soil of pH 7.9. The winter population was sown on 6 November 2023 and grown until 25 March 2024; the summer population ran from 18 April to 29 September 2024. Each population was established in three replicate plots with irrigation supplied as needed but fertilizers, herbicides and pesticides deliberately withheld to maintain near-natural conditions. Tagged plants were observed daily throughout both seasons, with developmental timing expressed in days after sowing, plant height measured at representative stages, and thermal accumulation calculated as growing degree days using a base temperature of 5 °C and an upper threshold of 45 °C.

The results exposed a striking seasonal divergence in developmental strategy. During the vegetative phase, the summer population was the clear front-runner. Cotyledons unfolded at 12.0 days after sowing compared with 16.5 days in the winter population, the first true leaves appeared nearly a week earlier, and nine or more leaves had developed by day 22.0 versus day 30.7. Branching told the same story: the first side shoot emerged at 25.5 days in summer plants against 35.4 days in winter plants, and stem elongation began at 45.7 versus 51.7 days. By the time winter plants had completed stem elongation at 78.1 days, the summer cohort had already finished the same stage twelve days earlier. Virtually every vegetative milestone was statistically significantly advanced in the summer population.

Then the tables turned. The moment the plants shifted from building bodies to making seeds, the winter population surged ahead. Inflorescence initiation occurred at 63.1 days after sowing in the winter cohort, a full thirty days before the summer population reached the same stage at 93.6 days. First flowers opened at 72.0 days in winter plants compared with 114.0 days in summer plants, and the entire flowering sequence, fruit development, fruit maturation and senescence followed in the same pattern, with every reproductive milestone significantly earlier in the winter population. Whole-plant death arrived at 140 days for the winter cohort and 164 days for the summer cohort. The winter plants, in effect, compressed their reproductive schedules to beat the approaching heat of spring, while summer plants lingered vegetatively much longer before committing to reproduction.

Thermal-time analysis added a deeper dimension to the story. Although the summer population reached vegetative stages sooner in calendar days, it required vastly more accumulated heat to finish its life cycle: 4261.18 growing degree days compared with just 1301.82 for the winter population. That enormous thermal budget reflected the summer cohort’s prolonged vegetative growth, delayed reproduction and greater final stature. Plant height itself diverged dramatically, with summer plants reaching a maximum of 226 centimetres against only 81 centimetres for their winter counterparts. In both populations, height increase was essentially complete by flowering, after which growth was redirected toward seed production, indicating that stem elongation is strategically front-loaded before the reproductive phase claims the plant’s resources.

The authors are careful about interpretation. Because each cytotype was grown during its natural season, temperature, photoperiod and other environmental variables were inherently confounded with chromosome number, so the observed differences represent phenological variation between seasonal cytotypic populations rather than proof that ploidy alone dictates developmental behaviour. The timing patterns nonetheless align well with known environmental regulation of flowering, in which temperature and photoperiod cues govern developmental transitions in annual plants. Higher summer temperatures plausibly accelerated vegetative growth, while the winter population’s rapid reproductive transition is consistent with short-day, cool-season flowering responses documented in the species since the classic photoperiod studies of Ramakrishnan and Kapoor in the 1970s.

Beyond its scientific value, the framework carries immediate practical weight. By coupling standardized BBCH staging with accumulated thermal time, farmers and researchers can predict when weed populations will germinate, flower and set seed, allowing herbicide applications, mechanical control and scouting operations to be synchronized with biologically vulnerable stages rather than fixed calendar dates. The team also mapped stage-specific ecological functions and risk windows across the life cycle: seedlings and young plants can serve as reservoirs for soil-borne pathogens and nematodes, dense flowering canopies create microclimates favourable for downy mildew caused by Peronospora variabilis, reproductive tissues support pollinators while facilitating vector-borne virus transmission, and senescent residues can harbour fungal inoculum and nematodes that carry over between cropping seasons.

The standardized coding also opens the door to precision agriculture technologies, including remote sensing, drone-based monitoring and automated growth-stage identification, all of which depend on objective, transferable developmental reference points. The authors caution that the study covered a single location and one growing season per population, so the framework should be validated across multiple years and climates, and common-garden experiments will be needed to disentangle cytotype effects from environmental plasticity. Still, the achievement stands: a plant that has both fed and frustrated humanity for millennia finally has a complete, reproducible developmental language, one that promises to sharpen everything from weed management to comparative phenology in a warming world where the seasonal rhythms of aggressive weeds will increasingly determine who wins the contest for the field.

Subject of Research: Phenological staging of seasonal hexaploid and tetraploid populations of the weed and vegetable species Chenopodium album using the extended BBCH scale

Article Title: Phenological documentation of two seasonal cytotypic populations of Chenopodium album L. using extended BBCH scale

Article References: Rathore, R., Kumar, V., Shankhwar, A. K., Faizan, M., Alam, P., Manzar, N., & Bisarya, D. (2026). Phenological documentation of two seasonal cytotypic populations of Chenopodium album L. using extended BBCH scale. Discover Plants, 3(1), Article 391. https://doi.org/10.1007/s44372-026-00861-0

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00861-0

Keywords: Chenopodium album, BBCH scale, phenology, cytotypes, hexaploid, tetraploid, weed ecology, growing degree days, seasonal populations, weed management, plant development, agroecosystems