You can do it pretty quickly by using Google to search the whole forum. Click on Search, which is next to APC Home. Then chose "Search Site / Google and select the aquaticplantcentral.com button. Type in "hornwort plantfinder". If you chose the button next to Google, the search will include the whole web, but if you chose aquaticplantcentral.com, google limits the search to APC. This will give you every post where both plantfinder and hornwort are together, but it does not take long to pick out the actual plantfinder article on hornwort.