Thanks for that. I've always wondered what an aspen tree was and simultaneously loved poplars.

I found this useful description of the two varieties:

"The quaking aspen (Populus tremuloides) was named by the eminent French botanist Andre Michaux in his 1803 Flora Boreali-Americana. The scientific name tremuloides means "like tremula," commemorating its resemblance to the European form (Populus tremula). Subtle geographic variations have led some scientists to split aspens into multiple species, while other scientists have considered assigning all aspens to a single circumboreal superspecies. Given the difficulty of determining the age of individual aspens, the possibility of a close relationship to one ancestral form must be kept in mind.

The generic name of aspen, Populus, is from a Latin word meaning "people, a great number," for the similarity between the continuous motion of a crowd and the trembling of leaves.

The word "aspen" is itself an old word, encoded in some Indo-European languages for thousands of years. Originally the tree was known as "asp" with "aspen" being used as an adjectival form. Metaphorically, the adjective once referred to trembling, especially in fear or anger (as in Chaucer's, "That lyk an aspen leef he quook for ire")."

http://arts.envirolink.org/literary_arts/DavidLukas.html