Shi Wei, “the leather of stone”

Shi Wei reads word for word “the leather of stone”, and the name is an exact description: it is a fern that grows on rocks and tree trunks, whose thick, firm, leathery fronds really have the feel of leather. Their underside is covered with a reddish felt of star-shaped hairs, which earned the genus its botanical name, Pyrrosia, “red”. The frond of Pyrrosia lingua is used, olive green above, which can be harvested in any season, then dried in the shade or the sun. An ancient text gives a quality criterion unlike any other: the best fronds grow on rocks where one hears neither the sound of water nor human voices. It appears in the very oldest Chinese work on materia medica.

Helping water flow, without drying

In Traditional Chinese Medicine, the fern is slightly cool, bitter and sweet: bitter brings down and clears, sweet spares and moistens. This is its signature: it clears Heat and Dampness from the lower body without drying, where purely bitter, cold herbs leave the passages raw, and tradition considers it more moderate than its neighbours for this reason. Its first and oldest action is to make urine flow and to open the waterways; linked with the Bladder, it removes Heat and Dampness there while moistening the passage. It is readily paired with plantain seed.

From the Lung to the Bladder

The pair of its meridians, the Lung and the Bladder, seems strange: the highest and the lowest. A classical text gives the most elegant explanation: when the Lung Qi descends and transforms, the waterways flow. For tradition, the water below depends on the Lung, which brings it down, and the fern works at both ends of the same movement. It clears Heat from the Lung and brings its Qi back down, while its sweetness moistens. Modern research takes a particular interest in quercetin and kaempferol, two flavonoids it contains.