There are currently two types of scythe in Wildernether: the Blackstone Scythe, and the Soul Scythe.
Scythes allow you to harvest Wildernether plants from Nether Sprouts, Warped Roots, Warped Fungi, Warped Vines, Crimson Roots, Crimson Fungi, Crimson Vines, and Shroomlight.
Using the Soul Scythe, you can a 200% increased chance to find secret plants. There are 5 in total, and they have no purpose other than as a collectible (or to show off).