80,000 plants, landscape architects, etc.

[ilima]

Well, you generally don't learn them all at once. You can cram for an exam, but to learn the names and retain them you can only learn so many at a time. There are also things like pneumatic devices and abbreviations.

I used to do botanical/ecological surveys in Montana over the summer when I was in and right after college. We coded everything by 4 and then later 6 letter codes, and I tended to learn those before the full name. For example, one habitat type was known as ABLA/MEFE. I knew what what plant ABLA was (fir tree) and what MEFE was (shrub) but it was a couple weeks in that I remembered ABLA=Abies lasiocarpa and MEFE=Menziesia ferrugina.

The soil conservation service (or whatever it's named now) uses six letter codes (first three letters of the genus+first three of the specific epithet) for all plants. A number is added if more than one species have the same 6 letter code.

Now, horticultural varieties--that's a whole 'nother ball of wax.

[Zen]

There are also things like pneumatic devices and abbreviations.

Pneumatic devices like a jackhammer to pound the names into your short term memory?
I think you mean mnemonic devices

[NbyNW]

Rote memorization.

When I took plant ID, the courses were divided into spring & fall (this was in the Bay Area, so if something flowered during one part of the year, that was the semester it was taught).

We made flashcards for study aids. One side had a dried, pressed plant specimen mounted on it under clear contact paper. The other side had botanical name, common name(s), and other descriptive information about the plant -- family, genus, height, form, flower/fruit type, area of distribution, whether it provides food or habitat, etc., etc.

I also spent time volunteering at the local arboretum, and that was a great way to get familiar with the plants and how they look different throughout the year.