from The Century Dictionary.
- noun A crystallizable substance (C20H22O8) found in the bark, root, and leaves of the aspen, Populus Tremula, along with salicin. It forms delicate white needles, which have a sweet taste like that of licorice.
from the GNU version of the Collaborative International Dictionary of English.
- noun (Chem.) A glycoside, related to salicin, found in the bark of certain species of the poplar (Populus), and extracted as a sweet white crystalline substance.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun organic chemistry A
glycoside, related to salicin, found in the barkof certain speciesof the poplar(Populus).
from Wiktionary, Creative Commons Attribution/Share-Alike License
Aspen contains salicin and populin, which have properties similar to aspirin in reducing fever, pain and inflammation.
In the willow and poplar,  a crystalline, bitter substance, salicin or populin, is found.