UPDATE: This fix is now bundled with the unofficial community patch starting with version 1.2, so it is no longer necessary to install it separately. You can get the community patch from here:http://steamcommunity.com/app/223510/discussions/0/648812916771880184/
Download my BotanicalBadAssPatcher.exe from here:https://github.com/DarkStarSword/miasmata-fixes/releases/tag/botanical-v1.0
Run it and follow the instructions on screen to point it at Miasmata.exe and patch the game, then play the game and collect all 36 different types of plants/fungi to unlock the achivement.
Despite the fact that the achievement description claims that it only requires 32 plants/fungi, it actually requires all 36 different types of plants that are in the game. They do not have to be researched to unlock it, but the "I discovered..." entries must be in your journal.
If you have already discovered all 36 types of plants, you should be able to trigger this achievement by picking up a note (like the lab or cartography tutorial notes), or re-researching any plant.http://steamcommunity.com/sharedfiles/filedetails/?id=197690566
Don't forget to also grab the unofficial community patch from here to fix a number of other problems with the game:http://steamcommunity.com/app/223510/discussions/0/648812916771880184/
-- ALTERNATIVE WAY TO PATCH THE GAME --
Most people should just use the BotanicalBadAssPatcher I posted above. But, if you would prefer to patch the game manually, you will need to open Miasmata.exe in your favourite hex editor (back it up first!), go to address 0x1321F5 and replace the byte there with 0x73. In the ascii view you should see that is replacing a null byte with an 's' to complete the word "plants". Thankfully, there is enough padding after that string that we don't need to rearrange memory at all to fix this.