Rheum rhaponticum : Sustainable cultivation Options in Central Europe

1. Introduction

Rhubarb root extract is a natural substance obtained from the roots of plants in the Rheum genus. It has a long history of use in traditional Chinese medicine (TCM) and herbal pharmacology.^1-3 Rhubarb root extracts are considered herbal or phytoextracts as they are plant-derived extracts that contain biologically active compounds, which can then be used as a sustainable source for innovative products. ⁴ However, while rhubarb is often cultivated for its roots, the aboveground parts of the plant may also be used for health food or other additives as they are rich in active ingredients and nutrients. ⁵

Medicinal natural resources are considered the basis of health care for 80 % of humanity. ⁶ Depending on definition and counting methods applied, between 36,000 and 50,000 plant species are used medicinally worldwide. ⁷ 70 % of these plants come from wild collection. Germany ranks first in the EU in the trade in medicinal plants, which speaks in favour of the high esteem in which this medical sector is held. ⁷ In the USA, Rhubarb first appeared on the mainstream channel’s top 40 herbal supplement ingredients list in 2021, ranking 39th, after sales more than doubled from 2020. The herb experienced two years of sales declines in 2022 and 2023, but climbed to rank 29 in 2024, after a 29.7% sales increase to $12.8 million. ⁸ This marks the highest sales ever recorded for this ingredient in mainstream retail stores and the third-largest percentage sales gain in this channel in 2024. In 2024, nearly 78% of rhubarb supplement sales, approximately $10 million, were attributed to products marketed for menopause support, representing a 21.5% increase over the previous year. ⁸ This significant rise in market demand highlights the growing need for rhubarb root cultivation.

It is important to distinguish Rheum rhaponticum from Rhaponticum, as Rhaponticum is a separate genus within the Asteraceae (tribe Cardueae). ⁹ Despite similar names, they belong to different families and differ in both root and aerial metabolites. Plant monographs are detailed, standardized scientific documents describing a specific plant’s identity, active ingredients, effects, areas of application, contraindications, potential side effects, interactions, dosage and pharmaceutical form. They aim at establishing official standard for herbal medicines to ensure quality and consistency and to serve as reliable scientific reference for safety and efficacy. Plants with adequate evidence of efficacy and safety are assigned positive monographs. ¹⁰ Plant monographs are prepared and published by expert committees, scientific institutions, or regulatory bodies that evaluate research data on medicinal plants. Monographs are available from the World Health Organisation (WHO), the Herbal Medicinal Products Committee (HMPC) of the European Medicines Agency (EMA), ¹¹ the European Scientific Cooperative on Phytotherapy (ESCOP), ¹² or from Commission E (authorisation and preparation commission set up at the Federal Institute for Drugs and Medical Devices (BfArM) in Germany ¹³ ). Currently, monographs on the following rhubarb root extracts are available: rhei radix from Rheum palmatum L. and Rheum officinale Baillon radix for the therapeutic area of constipation. While no official monograph on Rheum rhaponticum is currently available, the plant was included in the S3 guideline “Peri- and Postmenopause - Diagnostics and Interventions” in Germany in 2020. ¹⁴ The S3 guideline is part of the national system for clinical practice guidelines and represents the highest level of methodological rigor. Treatments listed in the S3 guideline have to be fully evidence-based, including systematic literature reviews, ¹⁵ critical appraisal of the available evidence, and formal consensus procedures. The purpose of this paper is to describe the taxonomy of Rheum rhaponticum, and to review current evidence on cultivation, propagation, and postharvest strategies to evaluate sustainable, regionally adapted production in Central Europe that ensures high quality, supply security, and biodiversity protection.

2. Authentication and Determination

The earliest culinary rhubarb varieties were likely hybrids of R. rhaponticum L., R. undulatum L. (syn. R. rhabarbarum L.), species initially introduced to Europe for medicinal use, and the unidentified R. hybridum.^16-18 Authentication of commercial herbal products plays a very important role to ensure correct species identification, consistency of active compounds, for safety reasons including avoidance of contaminants, for regulatory compliance, and to grow consumer trust and maintain brand reliability. ¹⁹ As the chemical composition of a plant may change depending on soil, climate, and harvesting conditions, provenance and origin determinations,^20-22 as well as characterizations^23,24 matter. Molecular analysis of Rheum species, ²⁵ including studies on molecular phylogeny, recent radiation and evolution of genus’s ²⁶ gross morphology, and extensive hybridization, ²⁷ assist in clarifying the phylogeny and accurate identification of Rheum species. ²⁸ A distinction must be made between plant extracts in foods.^29-31 Mixtures of natural substances with a complex spectrum of ingredients require continuous stability testing to ensure high quality standards. ³² Compliance with the Supply Chain Due Diligence Act and other regulations governing value chains for herbal medicinal products is mandatory. ³³ Adulteration can unfortunately be of concern despite strict quality assurance measures. Shen et al (2024) evaluated 63 rhubarb samples (five Polygonaceae species: Rheum tanguticum, Rheum palmatum, Rheum officinale, Rumex japonicus and Ru. sp.) and found that 33.3% of the samples consisted of adulterants. ³⁴ Rhubarb raw materials are frequently mixed or fully replaced by Rumex japonicus and other Rumex spp., which do not only differ genetically but are also considered chemically inferior to genuine Rheum species, resulting in a potential loss of efficacy.^35,36

Climate change, climate stress and its effect on plants^37-39 and humans, ⁴⁰ species extinction, declining biodiversity, endangered seed diversity also due to concentration in the seed sector, where the three largest seed companies (Bayer/Monsanto, Du Pont, Syngenta) currently dominate 40 % of the market, are threatening developments. ⁷ Small farmers still produce 70% of the world’s food, 1.5 billion of whom are dependent on their own seeds. ⁷ However, patents on seed increasingly restrict their ability to exchange and multiply their own seeds. ⁴¹ Also, insect populations have declined by 70% over the last 15 years, including many pollinators and beneficial insects. ⁷ Contributing factors include the destruction or modification of habitats. Also, pesticide use has increased dramatically, for example by over 50% since 1995 in Germany alone, where currently over 100,000 tonnes of pesticides are applied every year. ⁷

3. Wild Collection and Cultivation

Wild-collected medicinal herbs are often the only source of income for Indigenous communities and provide their clients not only with relatively favourable prices but also access to traditional knowledge about the use of the plants. ⁷ However, there is often a risk of overexploitation of the plant populations or even complete eradication, as well as the possibility of physical or chemical contamination. Rheum rhaponticum L. is a perennial species with a large, slow-regenerating root system, potentially making it particularly vulnerable to overharvesting. ²¹ It is considered a protected species ⁴² and listed as critically endangered in the Red Data Book of the Republic of Bulgaria. ⁴³ In addition, unclear local ownership structures and the often inadequate infrastructure can create uncertainty and result in supply bottlenecks.

However, in some countries or areas, wild collection is well-organized, the ecological principles guiding sustainable harvesting, and the economic significance of this practice for the medicine and health sector is immense. For example, in Germany commercial wild collection of medicinal plants is applied,^44,45 as well as wild collection of medicinal plants, ⁴⁶ and ecological wild collection. ⁴⁷ In particular, the value of ecological wild collection as both an environmentally responsible method and an important contributor to the pharmaceutical, herbal remedy, and wellness industries are described. ⁴⁸

Possible sources of raw materials for medicinal and cosmetic plants include.

• Biodynamic cultivation and wild collection in the company’s own gardens

The organic cultivation of medicinal, ⁴⁹ aromatic and cosmetic plants^50,51 offers particular benefits. It can tap into the exceptionally rich biodiversity with tens of thousands of species available from nature for cultivation. This broad diversity results in numerous opportunities for selection and development, including breeding efforts and - after thorough research into optimal growing conditions – the production of high-quality active ingredients free from any problematic substances such as pyrrolizidine alkaloids. The cultivation of wild plants has a long-standing tradition, and as a result, there is considerable expertise in the processes required to transition a species from wild to cultivated. This begins with an in-depth study and characterization of the plant’s natural habitat and the conditions in which it thrives. These findings are then translated into cultivation protocols, which are first tested through field trials. It is important to distinguish between in situ and in vitro cultivation systems. In situ cultivation refers to field-based production under natural soil and climatic conditions, whereas in vitro approaches include micropropagation and subsequent greenhouse or controlled-environment cultivation. Both systems are relevant for Rheum rhaponticum and are addressed in this review.

Among other aspects, plants from different origins are also tested. This is followed by several years of cultivation in gardens or greenhouses. Including seed production and selection (e.g. according to HORTUS principles), until a gene pool is established that meets all necessary requirements. ⁷ Some examples of such projects include.

• Selection cultivation

Both harvesting options, plant cultivation as well as wild collection, display advantages and disadvantages: Cultivating medicinal plants offers the benefit of a reliable supply of raw materials and reduced collection pressure on wild stocks. In addition, it allows for breeding, enabling the development of genotypes that are optimized for specific uses. While local value creation is a potential benefit, significant investments are also required in land as well as in the development of cultivation and harvesting technologies, which can ultimately increase production costs. Moreover, targeted breeding may reduce genetic diversity, which could be disadvantageous in the long term given environmental changes such as climate fluctuations. ⁷ Another aspect to consider is the prevention and control of pests in an economically viable, environmentally sound, and socially acceptable way. Integrated pest management is the core approach in the cultivation of medicinal and aromatic plants, prioritizing preventive, biological, biotechnical, and agronomic measures, while chemical pesticides should be used only as a last resort and under strict residue limits. Guidelines on integrated pest management in the medicinal and aromatic plant sector also stress the need for regular crop monitoring, thorough documentation, use of resistant varieties where possible, and continuous evaluation to ensure product safety, quality, and environmental protection. ⁵³

The top priority when cultivating is to align practices with the climate and soil conditions of the plant’s natural habitat, particularly for field-based (in situ) cultivation systems. Since not all details can be predicted, it is essential to conduct experiments to allow for assessment of the following areas.

• Generative propagation, e.g. breaking of dormancy mechanisms

Preliminary research on the cultivation of Hydrastis indicated, among other findings, that generative propagation is time-consuming and challenging, whereas vegetative methods can yield high-quality plants under certain conditions. ⁵⁹

4. Rheum Cultivation

Cultivation guidelines exist for medicinal rhubarb,^60,61 and for dedicated areas in Central Europe, specific field-based cultivation data are also available. ⁶² Rheum species can be diploid and tetraploid. ⁶³ The aforementioned cultivation instructions for medicinal rhubarb provide detailed guidance on rhapontic rhubarb.^60,61 To our knowledge, however, no published cultivation guidelines exist for Rheum rhaponticum itself, although references to such work can be found. ⁶⁴ It is noted that rhaponticin is extracted from plants approximately two years old and is used in gynecology. The benefits of plant-derived estrogens include their ability to regulate human hormone metabolism similarly to endogenous hormones, reduce the risk of breast cancer, and, unlike synthetic estrogens, be broken down in sewage treatment plants. Current rhaponticin imports from China no longer meet pharmaceutical industry standards, as the active ingredient content has declined from 11% to less than 5% in recent years. With growing consumer acceptance of herbal-based products, there is an increasing interest in producing these raw materials in Germany. Sustainable cultivation of phytopharmaceuticals has been analysed for Baden-Wuerttemberg, Germany and Rheum rhaponticum has been identified as particularly suitable.^65,66 Therefore, the cultivation of Rheum rhaponticum (Rhapontic rhubarb) in Central Europe is possible due to favourable climatic conditions and may be of increasing interest due to its increasing market demand. Cultivation of the plant in Central Europe may also simplify quality and authenticity control. Researchers estimate that optimized rhubarb cultivation could cover approximately 1,200 – 2,400 hectares. ⁶²

5. Rheum Rhaponticum Cultivation

Wojtania et al (2023) ¹⁶ evaluated the response of micropropagated Rheum rhaponticum plantlets to different growing media and light conditions compared to a control group (natural sunlight). Their study demonstrated that the early ex vitro growth of micropropagated rhubarb plantlets is significantly influenced by the type of growth substrate and LED light quality, with a high-EC peat substrate and a combined red, blue, green, and far-red LED spectrum producing the most favorable growth and soluble sugar accumulation. Among the LED treatments, the R+B+G+FR combination promoted the best overall growth, biomass, and sugar content, while white LED light resulted in the highest phenolic compound and anthocyanin levels, which are associated with antioxidant activity. The findings highlight the potential to optimize rhubarb planting material production through tailored substrate choices and specific light spectra, especially emphasizing the role of white LED light in enhancing phenolic biosynthesis.

Another study examined how photoperiod and temperature affect growth and dormancy in micropropagated Rheum rhaponticum ‘Raspberry’ plantlets. ⁶⁷ Plantlets grown under a 16-hour photoperiod and moderate temperatures (17–23 °C) showed active leaf and rhizome growth without entering dormancy. In contrast, a 10-hour photoperiod or elevated temperatures triggered rapid growth cessation, leaf senescence, and the onset of endodormancy, similar to effects previously observed in greenhouse-grown rhubarb seedlings in spring. Physiological and molecular analyses indicated that dormancy induction involved increased abscisic acid (ABA), starch accumulation, and upregulation of genes related to carbohydrate metabolism, ABA signaling, and stress responses. In another study, the authors investigated dormancy regulation in micropropagated ‘Malinowy’ rhubarb plantlets, assessing changes in carbohydrates, total phenolics, endogenous hormones and gene expression during dormancy induction and release. ⁶⁸ Dormancy was induced under high temperature (25.5 °C) and long-day (LD) photoperiod conditions, coinciding with leaf senescence and elevated starch, total phenolic, ABA, IAA and SA levels. Breaking dormancy required five weeks of cold treatment at 4 °C (with longer storage producing faster, more uniform sprouting and longer stalks), while non-cooled rhizomes showed no growth response. At the molecular level, dormancy release was characterized by increased expression of genes such as AMY3, BMY3, SUS3, BGLU17, GAMYB (carbohydrate metabolism) and ZEP, ABF2, GASA4, GA2OX8 (hormone metabolism/signaling), linking carbohydrate and hormone metabolism with dormancy status in this rhubarb cultivar. These findings highlight that careful control of temperature and storage duration is crucial for optimizing rhubarb yield, uniformity, and stalk length during harvest.

Salata & Kozak (2013) evaluated yield and morphological characters of Rheum rhaponticum L. ‘Karpow Lipskiego’ and found that vegetative methods produce more uniform plants with greater crown development, more leaves, and higher early and total petiole yields than seed propagation. Overall, cultivation of vegetatively propagated plants proved to be an effective method for producing high-quality planting material, delivering the highest early yield and making it well suited for establishing productive commercial rhubarb plantations. ⁶⁹

Clapa et al (2020) developed an efficient micropropagation protocol for Rheum rhabarbarum, achieving a shoot proliferation rate of about 5.0 ± 0.5 and rooting of 96% in vitro, followed by successful acclimatization (90%) ex-vitro. ⁷⁰ Genetic fidelity of the micropropagated plants was confirmed using SRAP markers, showing identical banding profiles to the mother plant (100% similarity). The study also compared phenolic compound profiles between field-grown and in-vitro propagated plants across rhizome, petiole, and leaf tissues, identifying high levels of compounds such as catechin, p-coumaric acid, rosmarinic acid and resveratrol (229–371.7 µg g^-1 in rhizome extracts). The authors conclude that in-vitro propagation of R. rhabarbarum offers a reliable route for large-scale production of true-to-type planting material with valuable bioactive compound content. The study by Clapa et al demonstrated that the phenolic composition of Rheum rharbarbarum plant extracts can differ between in vitro propagated and field-grown plants. ⁷⁰ Wojtania & Mieszczakowska-Frąc (2021) developed an efficient in vitro propagation protocol for the selection of rhubarb ‘Malinowy’, enabling rapid, virus-free clonal multiplication of high-quality planting material. ⁷¹ Optimized cytokinin (especially meta-topolin) and sucrose conditions supported efficient shoot multiplication, rooting, and ex vitro establishment of phenolic-rich plants.

Kozak & Sałata (2011) ⁷² assessed the effects of four cytokinins (BA, kinetin, 2iP, TDZ) on in vitro shoot multiplication of rhubarb and subsequent ex vitro acclimatization and field growth. They found that BA at 11.1–22.2 µmol·dm^-3 produced the highest number of axillary shoots, while kinetin (4.7–11.6 µmol·dm^-3) and 2iP (12.3 µmol·dm^-3) promoted strong shoot elongation and larger leaves; by contrast, all TDZ treatments significantly inhibited elongation. Rooting was adversely affected by BA and TDZ, but media with kinetin or 2iP (and the hormone-free control) achieved 100% rooting, and plants propagated with 2iP showed the most uniform and vigorous field growth after eight months.

R. khorasanicum roots collected in December, February, and April were found to display extracts with substantial total phenolic and flavonoid contents, along with antioxidant activity. ⁷³ The sample harvested in April showed the highest levels of phenolics and flavonoids, and this corresponded with the strongest antioxidant (FRAP assay), antibacterial, and cytotoxic effects on cancer cell lines (C6, A549, HT-29). This shows that harvest timing significantly affects the bioactive compound content and biological activity of the plant: later harvest (April) gave better potency. For practical application, this means that to maximize therapeutic (antioxidant/antibacterial/cytotoxic) potential from R. khorasanicum roots, scheduling harvest around April (in the given climate/context) is advantageous compared to earlier months. Kalisz, et al (2020) compared Red Malinowy and Viktoria varieties of rhubarb, obtained in spring (May) and autumn (September) harvest under climatic conditions of Poland and showed that the harvest date significantly affects the content of polyphenolic compounds in edible stalks of rhubarb. ⁷⁴

Environmental factors such as light quality/intensity, temperature, and stress conditions have been found to significantly influence the biosynthesis of stilbenes in plants. Under more stressful or sub-optimal conditions (e.g., low temperature or UV-light exposure) plants ramp up stilbene production, suggesting these compounds act as protective/defence metabolites. ⁷⁵ Therefore, management of environmental factors can be used to boost stilbene levels in crops for enhanced nutritional or phytochemical value. However, species/genotype differences, as well as timing and tissue types affect stilbene accumulation. Hence, targeted cultivation strategies are needed to maximize yield of these bioactive compounds.

Sumbembayev et al (2023) examined seed morphological (size, weight) and external structural features for 7 species of Rheum from Kazakhstan. ⁷⁶ Rheum species show measurable differences in seed size, weight, and structure, influenced by habitat and ecological conditions. Some seed traits, especially in section Ribesiformia (R. cordatum, R. maximowiczii), were found to be stable and useful for species identification. Most species occupy narrow habitats, limiting morphological variation, but seed morphology still reflects species boundaries. Overall, seed morphometry can serve as a reliable tool for identifying and distinguishing Rheum species, particularly in cases where other plant traits are hard to assess (e.g., outside the flowering season). This may support accurate species identification and lead to taxonomic clarification. It is also of importance for producers or processors of rhubarb (Rheum rhaponticum) to note that the application of a controlled ozone gas treatment immediately post-harvest may help retain moisture, reduce spoilage, improve texture (mechanical robustness), and maintain or boost nutritional/antioxidant quality. ⁷⁷ Ozone treatment is relatively low cost and may offer an alternative to refrigeration especially in supply chains where cold storage is limited. Because microbial load is reduced, ozone treatment can be part of a post-harvest sanitation strategy, potentially reducing reliance on conventional chemical sanitizers or fungicides. Ozone treatment therefore may provide a practical, safe, and economical method to improve post-harvest storage and marketability of rhubarb. In vitro cultures are important for rapidly multiplying value genotypes and producing plants free of viruses. The study “Optimizing the Micropropagation of Red-Stalked Rhubarb Selections: A Strategy for Mass Production of High-Quality Planting Material” aimed to develop an in vitro propagation method for six rhubarb selections. ⁷⁸ The highest content of anthocyanins and rhaponticin was found in Raspberry selections. On the other hand, Leader selections were characterized by the highest content of resveratrol and phenolic acids. Positive effects of Ethylene in Adventitious Root Formation of Red-Stalked Rhubarb in Vitro have been observed. ⁷⁹

Yorkshire Forced Rhubarb is cultivated in the Rhubarb Triangle, which is a 9-square-mile (23 km²) area of West Yorkshire, England famous for producing early forced rhubarb. In 2010, Yorkshire Forced Rhubarb was awarded Protected Designation of Origin (PDO) status by the European Commission’s Protected Food Name scheme. ⁸⁰ Rhubarb plants of the varieties ‘Timperley Early’, ‘Stockbridge Harbinger’, ‘Reeds Early Superb’ or ‘Fenton’s Special’, ‘Prince Albert’, ‘Stockbridge Arrow’ and ‘Victoria’ are currently mostly used for the cultivation of this rhubarb speciality. The plants are usually propagated by division and must be cultivated for two to three years under the special climatic and soil conditions until they are suitable as forcing rhubarb. During this time, no stems are harvested so as not to weaken the plant during this phase. ⁸¹

In our own experience, Rhapontic rhubarb has been grown and used for over 70 years, ⁸² long before the 1992 Convention on Biological Diversity in Rio.^83,84 Overall, the cultivation of Rheum rhaponticum encompasses both in situ (field) and in vitro (micropropagation and greenhouse) systems, with field cultivation representing the primary approach for large-scale production of raw material. In our Rhapontic rhubarb cultivation projects in Baden-Wuerttemberg, a state in Germany,^85,86 Stolbur transmission by Cixiidae affected rhubarb roots at cultivation sites both in north-western Baden-Wuerttemberg (Kraichgau) and in central Baden-Wuerttemberg (near Stuttgart). We were able to avoid such potential negative effects of outdoor cultivation in vertical farming projects.^87,88

6. Conclusion

The increasing demand for rhubarb-based phytoextracts highlights the need for sustainable and regionally adapted cultivation strategies. Optimizing propagation methods, environmental conditions, and postharvest practices can ensure high-quality raw materials while reducing reliance on imports and preserving biodiversity. Central Europe offers favorable conditions for large-scale production according to Good Agricultural and Collection Practice, positioning Rheum rhaponticum as a promising crop for future phytopharmaceutical development. Unfortunately, despite the long history of use of Rheum rhaponticum, systematic data on its agronomic requirements and optimized cultivation strategies remain remarkably limited. Future research should therefore focus on controlled cultivation approaches, including vertical farming systems, and on targeted selection programs aimed at identifying lines with maximal accumulation of bioactive constituents. In addition, harmonized evaluations of cultivation parameters across regions could lead to the development of standardized cultivation diagrams, control points, and reliable visual summaries for successful cultivation of Rheum rhaponticum.