If rarest, then I guess mine would be an “extremely rare”, the Hairy-nosed Otter (Lutra sumatrana) https://www.inaturalist.org/observations/334179371 with two sightings in less than a year. Researchers have described it as the rarest otter in Asia, with only a few scattered populations across its range and extremely low encounter rates.
Looking forward to more sightings if the habitat remain undisturbed and intact.
Wonderful! And you got so many nice, clear photos, from different angles, too!
a Canvasback x Redhead hybrid drake is probably the rarest critter I have ever observed and photographed. It was a perfect hybrid, as each of its features looked to be exactly between that of a Can and that of a Redhead. Even the irises of its eyes were partially red like a Can’s and partially yellow like a Redhead’s.
I’m not sure what it is, I have seen quite a few priority listed plants and endangered fauna species though.
Probably something not really rare at all, but if the ID is correct, only the second inat observation of it. I was making coffee yesterday morning, but noticed some white powder all over the top of my coffee bean bag. Then I noticed that the powder was coming out of the wood clip I use to keep the bag shut, and that the clip had several holes - and something was peeking out of one of the holes! Now of course I spent the next half hour splitting the clip with a knife until the beetle fell out and then I took 100ds of pictures (99% just completely blurry) of the little guy running around until he had enough and flew away… I didn’t expect the observation to ever get to species since usually I think beetles need dissection for that, but only hours later someone gave it a species ID! Little adventures like this is why I love inaturalist 
Lyctoxylon dentatum is some Asian beetle usually found in bamboo, so considering I’m in Europe, I most likely bought him along with the clips already.
Putting flighty subjects in the fridge for a while often makes them more sluggish and easier to photograph.
I’ve added it to the “hitchhikers” project.
Probably Entomobrya petri, a springtail species which only got named in August 2025 and that only has ~50 observations on iNat.
…I have 6 of those 50 observations, by the way, and the only reason I’m not first on the leaderboard is because someone else got 13 observations of it :)
Probably this hopper.
Little dude looks unimpressive, but it’s the first and possibly only record of a living individual anywhere, evidently…
Don’t know the numbers for most of what I’ve seen, but I think a fairly good guess would be Cirsium joannae, which apparently only has ~200 individuals in the wild (as per correspondence with Darrin Gobble, user dee_gobbs).
As far as which species had the least observations, I think my observations make up the bulk of images for Cirsium harrisonii and Cirsium longistylum.
…..in case there’s any doubt of what my favorite genus is:
Probably the Great Egret × Great Blue Heron hybrid I saw at Vinoy Park in St. Petersberg several year ago. Apparently only a handful of wild documented cases exist in the world and this is one of them. Link to the observation is here: https://www.inaturalist.org/observations/338007266
What an amazing find! It’s so pretty! Welcome to the forum!
Thanks MK!
When I was in remote Northern Ontario, I happened upon some really strange mosses that I thought was a fungus at first. There were two species, Red and Yellow. Red apparently is more rare than Yellow, with only 89 observations. Though, Yellow is critically endangered, and has a 460 observations!
Behold! Splachnum rubrum, the Brilliant Red Dung Moss and Splachnum luteum, the Yellow Moosedung Moss!
wow! I get that their common names are derived from their preferred habitat, but I think they deserve lovelier names.
i have touched the largest known surviving eastern hemlock, the cheoah hemlock. i don’t think that really counts as rare, but dang what a tree!
I’ve always thought the name was funny! But I do agree. Something like Brilliant Red Umbrella Moss!
They’re by far one of the most colorful mosses we have in Ontario. Very eye catching in the wild.
New to this thread, but I’ve seen three animals that could be considered rare: the Eastern Barred Bandicoot (was declared extinct in the wild in 2013, but has been reintroduced to mainland Australia successfully).
The Florida Scrub-Jay, of which only about 1000 remain:
And last weekend I got a chance to see the Brush-tailed Rock Wallaby; estimates put their population in the wild at ~100. The ones I saw are wild, but are safely living their best life in a preserve that’s protected from foxes by an electric fence. I haven’t finished processing those photos yet though.
