The Cattail Knife
This knife is a marvelous tool I learned about at Cosumnes River Preserve in California. On days when the Habitat Restoration Team decides to remove cattails (Typha to provide open water for waterfowl, these tools are brought out by the bucketful. They are inexpensive, only about $5-10 each, and can slice through even the thickest plants. They also work well on herbaceous stems like mustards and thistles (use very thick gloves with the latter!). Of course, since they are so sharp, you can easily cut your hand off, so be careful.
Fibrous plant tissue dulls the blade quickly, so after a few hours of use the knife does not decapitate plants as easily. But just a few minutes with a file sharpens them back to a deadly edge.
You can get these knives at any medium sized hardware store.
--Barry Rice, TNC/GIST, May 2000