Wai Nian Song

Wai Nian Song does not match a standard entry in the principal Chinese materia medica references and is most plausibly a transcription error for Wan Nian Song, identified as Selaginella tamariscina, the resurrection spike-moss (family Selaginellaceae). It is a perennial lycophyte (a fern ally rather than a true fern) forming dense, cushion-like rosettes 5 to 15 centimetres across atop a stout, branched, scaly caudex of persistent old stem bases that resembles a small woody trunk. Numerous radiating, repeatedly forked branches bear two ranks of tiny, overlapping, scale-like green leaves; under drought the branches curl tightly inward and the plant appears dead, but re-expands and greens rapidly upon re-wetting, the basis of the colloquial name. The species inhabits exposed rock outcrops and cliff faces across much of China.