Do all the plants in Morrowind and Oblivion (with the exception of Nirnroot, of course) exist in real life? I recognise the names of a lot of the flowers as being real-world flowers but I am uncertain of some of them, such as the fungi.

Yes, to Oblivion, however they look nothing alike (except for a few of the trees). Not really to Morrowind. They have a few inspirations like the bittergreen plant I believe is loosely based on foxglove, or wickwheat being based on... well guess. But mucksponges? Giant Parasol's? Nothing real life about those.

Plants from the realm of Oblivion on the other hand...

some are and some arent..

Fantastic answer...
Morrowind plants, some are, some aren't. Most aren't
Cyrodil plants, most seem to be, some probably aren't. (Not too sure)
Oblivion plants. noooooooooooooo
Shivering Isles plants, no

Saint Jahn's Wort: totally doesn't have a real life counterpart. Completely original, and it's absolutely not jarring or 4th-wall breaking to see it in the game.

On the same note, Marshmerrow. They didn't even try.

Oh hell yes. Saint of whose?


Stinkhorns exist, by the way, and they grow in Oblivion.

As for Mucksponges, well, http://upload.wikimedia.org/wikipedia/commons/6/62/SpongeColorCorrect.jpg.

Actually, there is island on earth with some very morrowind like flora. (No mushroom trees, but it definitely feels morrowindish)

http://www.darkroastedblend.com/2008/09/most-alien-looking-place-on-earth.html

Thanks guys.

So, I guess it's a case of checking each plant on a case-by-case basis, then.

Actually I think they mispelled it, there is a plant called Saint John's Wort which has yellow flowers, and was used to treat depression.

Anyways many of the plants in Cyrodill are based off real-life plants, though their medical abilities are completely different. For instance Mandrake can be used to cure diseases, when in real life it is a very poisonus plants that does nothing like that. You also have Ginseng which is treated like a poisonus plant in the game, but in real life it is a very benificial plant used in cooking. Also another thing I noticed is that the plants in Cyrodill tend to be 10x bigger then the real ones on Earth.

They fixed it in the UOP, so misspelling or not, it should be John's for most of us. I doubt that marshmerrow was a misspelling, though. Why would they misspell their plants two games in a row?