Polypodium formosanum 'Cristatum' ET Fern is a member of the Polypodiaceae family and is native to China and Taiwan. This unique and interesting fern is also known as the Grub Fern and Caterpillar Fern. What makes this fern so unique is the rhizome. It does resemble E.T.'s finger a bit and we can understand where it got that name. The rhizomes are hard and creep along the top of the soil, sending out roots every few centimeter or so. This is not a fast growing fern and it will take a bit of time to get a full size plant. That can work in your favor if you're trying to keep it contained in a small pot or terrarium. It will thrive in a terrarium because it does appreciate the humidity, but remember to allow for water drainage. It can also be grown as an epiphyte, which is how is normally grows in its native environment. Polypodium formosanum is easily pruned as it ages so containing it isn't really an issue as it could reach heights of 18" or so.