Rhizome

A rhizome grows underground like a root, but it is a stem [1]. Ingredient records often name both parts: Health Canada's Rhodiola monograph lists the dry root and rhizome as the part used [3], and the European Union herbal monograph is titled for Rhodiola rosea "rhizoma et radix", Latin for rhizome and root [4].

Studies of Rhodiola's chemistry have centered on these underground parts. A 2010 review reported that about 140 compounds had been isolated from Rhodiola roots and rhizome [2], and a 2017 review names salidroside, rosin, rosavin and p-tyrosol as the main constituents of the rhizome [1].

The plant part is part of the identity of an herbal ingredient, alongside the species and the extract. The part named on a label or in a methods section is worth checking before comparing two products or two studies.

For Rhodiola, the extract matters as much as the part. A 2010 review noted that a number of clinical trials used repeated doses of one extract, SHR-5 [2]. Results from one named extract describe that extract; they do not automatically apply to every Rhodiola product.

When a study or label names "root", "rhizome" or both, it is describing which underground organ was harvested. The same habit of naming the part appears with other ingredients in this glossary, such as the stigma of saffron and the fruiting body or mycelium of mushrooms.

For the graded evidence, see Rhodiola rosea.

• Botanical extract
• Standardized extract
• Adaptogen
• Stigma (saffron)