Phytochemical Diversity, Extraction Methods, Analytical Profiling, and Quality Control of Rheum tanguticum (Maxim. ex Regel) Balf.: An Evidence-Stratified Narrative Review

Rheum tanguticum (Maxim. ex Regel) Balf. is one of three botanical sources of Dahuang and exhibits chemical and processing variability that complicates species attribution and quality assessment. This review aims to synthesize species-specific phytochemical, extraction, analytical, pharmacological, and quality-control evidence and to propose a research framework tailored to the product matrix. A targeted narrative search of PubMed, Europe PMC, DOI-linked publisher records, and official botanical and regulatory sources covered material available through 18 September 2026; evidence was classified as authenticated direct studies (A), species-derived isolates (B), comparative Rheum evidence (C), or the broader compound-level literature (D), with authentication uncertainty stated explicitly. The synthesis shows that reported extraction outcomes are not directly comparable: crude decoction yield, target-analyte recovery, and chromatographic purity measure different endpoints. The current Chinese Pharmacopeia includes a Dahuang monograph, but its drug-level status should not be mistaken for a validated R. tanguticum-specific chemical profile. Five free anthraquinones are analytically accessible compositional markers but are not species-specific identifiers; glycosides, sennosides, stilbenes, tannin-related chemistry, phenylbutanones, and polysaccharides require matrix- and evidence-specific interpretation. We conclude that no single marker establishes botanical identity, efficacy, or safety. A defensible research strategy combines official compliance with voucher-supported authentication, validated multi-class profiling, processing-sensitive measurements, and safety assessment. The proposed panels are research priorities, not validated release specifications.