You find a strange plant growing in your garden-so you photograph it, and contact your local university botany dept. What happens next-do you get the creit for this? Or does the botany professor (that you contacted) steal your thunder?
Not that I’d ever done this before, but if I needed dated proof of something, I sent a copy of it to myself in the mail. The sealed copy would bear a postmark dating when it was sent.
In this case, take a picture (even a digital one), print it out, and mail it to yourself. Then wait a week before contacting the botanist. That way if he does try to steal your thunder, hey look! You’ve got an ‘earlier discovery’ all for the mere pittance of 41-cents!
Tripler
If it ain’t enough to discredit him/her, it’s enough to raise the question of “Who was first?”
I say the botanist gets the credit. At that point you’re just some knuckledragging mouthbreather toting around some local flora. He’s the one that’s going to have to do all the damned work to figure out what it is, publish the papers etc. Just because it grew in your yard doesn’t mean squat.
What kind of “credit” do you want, exactly?
The botanist would collect the plant (or parts of it, particularly flowers, if there were only one), press it, and deposit it in an herbarium. Then he or she would painstakingly compare it to specimens of other apparently related species to ensure it was in fact different. This would also entail a comprehensive literature search to make sure the species had not been described before. In some cases, it might involve asking for loans of specimens from other herbaria, or in some cases visiting them.
If it was indeed new, the botanist would write up a very detailed description, comparing the key characters that distinguish it from related species. He or she would then send the article out to a scientific journal, where it would be sent for peer-review by other botanists. If accepted, it would be published and the name would be official.
What the botanist gets out of this is their name attached to the species name as the author of the description. For example, a new species of cherry would be listed in catalogs as:
Prunus novus Smith
The “credit” you would receive would usually just be acknowledgment in the article: “Smith would like to recognize the important contribution of ralph124c in first recognizing this species and bringing it to my attention.”
In special cases, the botanist might choose to actually name the species after you: Prunus ralphii Smith. This, however, is an important honor, and typically reserved for collectors who have collected a lot of specimens, other honored scientists, financial donors, drinking buddies, or girls you really really have the hots for.
Note that, although it is not forbidden, it is considered very poor form for a scientist who describes a species to name it after himself. If you did that, you would be ridiculed by your peers.
That’s so easily faked it doesn’t really prove anything. Send yourself an unsealed empty envelope, it gets postmarked, then put anything you like inside whenever you like.
Not if I had left it sealed and let the judge open it in court. Why would I open it if I already knew what was inside? 
ETA: Oh, I see what you mean. . . Certify and register that letter too, then.
Tripler
Judge Wapner, in my hand I have proof that Lee Harvey Oswald killed the aliens that landed on the moon with Neil Armstrong.
I may have no idea what I am talking about but I definitely read it once. It said that there are so many unidentified species that a child that studied their own suburban lawn for a summer would find about two new ones. Like I said, I have no idea if that is true but a person one a new species crusade could find a few of new ones on their own somewhere around where they live.
I was convinced that I found a new species when I dug a huge hole as a kid. I only identified what they were through Google 20 years later. They were Mole Crickets which were the damnedest insects I had ever seen. They are really strong and sort of personable. You can’t hold one in your hand without it forcing your fingers apart. They are cuter than they look in the picture. I couldnt find anyone including farmers in Louisiana that had ever seen one. It might have been a new species for all I know.
Probably not multicellular plants, at least in the US. However, if you extend it to things like mites, nematodes, and so forth that could be true.
I’ve just been putting together an exhibit here on newly described or undescribed species in Panama. I went through the beetle collections with an entomologist and without half trying he gave me 20 specimens in the collections that represent species that the experts haven’t gotten around to describing yet. There were dozens more represented by a single specimen; I didn’t want to take things that there was only one of, and besides entomologists generally won’t describe a species if they only have a single specimen of it.
It is quite easy here in Panama to go out and collect dozens of new species if you concentrate on the smaller and more obscure life-forms like small insects and soil organisms.
I’m in the middle of publishing with a co-author a new species description of a bird we found in Africa in 2003. New birds are pretty hard to come by.