Polygonum is a large genus encompassing many species, such as Polygonum cuspidatum (Japanese knotweed), Polygonum aviculare (common knotgrass), and others. In traditional medicine systems—especially in Chinese and some European herbal traditions—various Polygonum species have been used to support respiratory health, including bronchitis. For example, Polygonum aviculare has been described in traditional European herbal texts as an expectorant and anti-inflammatory agent, used to ease symptoms of coughs and bronchial catarrh. Similarly, Polygonum cuspidatum (Hu Zhang in Traditional Chinese Medicine) has been used for respiratory complaints, though more commonly cited for other indications.

The justification for using Polygonum species in bronchitis is therefore rooted primarily in tradition rather than scientific validation. Modern clinical trials or pharmacological studies directly supporting the use of these species for bronchitis are lacking. Some in vitro and animal studies suggest anti-inflammatory and antimicrobial properties in certain Polygonum species, which could, in theory, help with bronchial inflammation, but these findings are preliminary and not bronchitis-specific. Overall, evidence is limited to historical use and indirect pharmacological plausibility, with no robust scientific validation for bronchitis specifically.