Populus tremuloides Michx. - Salicaceae
quaking aspen, trembling aspen, American aspen, Canadian aspen, Amerikanische Espe

Deciduous tree, up to 20m high, native to North America (Canada, Rocky Mountains); bark greenish-gray; leaves on long stalkes (3-7cm), small (4-8cm), oval to nearly round, with small rounded teeth; flower at catkins (4-6cm long), produced in early spring before the leaves, dioecious.
http://en.wikipedia.org/wiki/Populus_tremuloides

„Poplar bark is a traditional medicine against rheumatoid arthritis and other rheumatic conditions, but also cystitis, diarrhoea and the common cold. The leaves and bark are used for urinary problems resulting from an enlarged prostate. Buds are used against chronic bronchitis and rheumatism and externally for treating superficial wounds, external haemorrhoids, frostbite and sunburn (and as an ointment for myalgia).“
[Medicinal Plants of the World. Ben-Erik Van Wyk and Michael Wink, Pretoria 2004, 252]

„The hot water extractives of the fresh smooth green bark, leaves, and leaf stem twigs of a diploid Populus tremuloides tree cut in June were fractionated by ethyl acetate extraction and polyamide chromatography. Crystalline components isolated in quantity included salicin, salicortin, 1-O-p-coumaroylglucose, tremuloidin, tremulacin, and salireposide.“
[Hot water phenolic extractives of the bark and leaves of diploid Populus tremuloides. Pearl, Irwin A., and Stephen F. Darling., Phytochemistry Vol.10(2), 1971 483-484]

The dried leaves contain condensed tannins (5-20%) and phenolic glycosides (salicin, salicortin, tremuloidin and tremulacin, 2-6%).
[Within-and between-year variation in early season phytochemistry of quaking aspen (Populus tremuloides Michx.) clones. Osier, Tod L., Shaw-Yhi Hwang, and Richard L. Lindroth., Biochemical Systematics and Ecology Vol.28(3), 2000, 197-208]

Populus tremuloides Michx.
Lounsberry, A., Rowan, E., A guide to the trees, t. 129 (1900) [E. Rowan]
http://plantgenera.org/species.php?id_species=1268109