The Bracts of Saussurea velutina (Asteraceae) Protect Inflorescences from Fluctuating Weather at High Elevations of the Hengduan Mountains, Southwestern China

Several members of the subgenus Amphilaena (Saussurea; Asteraceae) growing at high elevations in the Himalayan region have semi-translucent bracts covering their inflorescences, the function of which is not fully understood. We investigated the thermal benefits of these bracts in Saussurea velutina in situ in the Hengduan Mountains, SW China, and compared the reflectance spectra and anatomical characters of bracts and rosette leaves in the laboratory. After removal of bracts in the field the average inflorescence daytime temperature was 2.5 °C colder than in control plants with intact bracts. Manually opened treatment inflorescences grew slower and set significantly fewer seeds than control inflorescences with bracts intact. The mesophyll of bracts is a single cell layer with a lower reflectance in the infrared range than rosette leaves. We show that the semi-translucent bracts in S. velutina function to ensure warmer temperatures for floral and seed development at high elevations in the Hengduan Mountains.