Dunno… So I looked.
Found info on Aspen on indexing extras (very bottom of page).
Interesting read and I can see why they did not break it down into individual species since it would have really extended the listing.
Way I would approach this is to call it Popular, which seems to be all inclusive to popular, cottowood, and aspen.
Seems safe but that Low Flammability probably means tweaking the pews a little. (A is for Adventure).
Added: Info seen during this quest below:
For identification purposes, Populus species can be divided into two main groups: cottonwood (including poplars), and aspen.
And from Wiki:
Aspen wood is white and soft, but fairly strong, and has low flammability. It has a number of uses, notably for making matches and paper where its low flammability makes it safer to use than most other woods. Shredded aspen wood is used for packing and stuffing, sometimes called excelsior (wood wool). Aspen flakes are the most common species of wood used to make oriented strand boards. It is also a popular animal bedding, since it lacks the phenols associated with pine and juniper, which are thought to cause respiratory system ailments in some animals. Heat-treated aspen is a popular material for the interiors of a sauna. While standing trees sometimes tend to rot from the heart outward, the dry timber weathers very well, becoming silvery-grey and resistant to rotting and warping, and has traditionally been used for rural construction in the northwestern regions of Russia.
Happy Trails and Keep On Burnin’