As part of a science project, my daughter needed to prepare herbarium vouchers to substantiate her research. So, I made her a plant press.
CHECK YOUR LOCAL LAWS REGARDING COLLECTING BEFORE YOU PICK ANYTHING! Get proper permits etc.
Basically, I made two identical, incredibly simple frames.
Unfortunately, the first one I made wouldn't fit into a backpack for our collecting trip. It was 16" by 22".
The instructable photos document the building of the extra large version. The photo below is the finished project - It is 11" by 16 ". Same wood, same weight as the larger version (because I overdid it on the number of boards I used!). If I had to do it again, I would use ChrysN's Pocket Flower Press instructions https://www.instructables.com/id/Pocket-Flower-Press/
, but make it larger and drill holes in the top and bottom pieces of wood to lighten the load and allow for air circulation..