Firs, Pines, and Douglas-firs, oh my!

'Tis the season when many people purchase decorative conifer trees; otherwise they own some ersatz version thereof. No option exists in our household because Mrs. Phactor is of the most firm opinion that only a natural tree will do. On an ecological basis cut conifers are grown as a crop and can be fully recycled. So here is your holiday conifer primer. 1. Evergreen is not synonymous with "pine tree" or "conifer". 2. The vast majority of trees sold this time of year are firs, douglas-firs, or pines, and these are three different genera (Abies, Pseudotsuga, and Pinus respectively). 3. Douglas-fir is not a true fir, but most confusingly it's also called Oregon pine and Douglas spruce. See the problem with common names?
Here's how you tell these three genera apart. One pines needles are in clusters or bundles of 2, 3, or 5. The other genera have needles borne singly upon the twigs. The common pine species sold as cut trees have two (Scotch) or 5 needles (white pine). Firs and Douglas-firs have different buds at the end of twigs. Firs have resinous buds, that is coated in resin, and rounded in shape. Douglas-firs are smooth, dry, and conical. Distinguishing among the various species of firs is too tricky for verbal descriptions.