A nature rune obtained in the Runespan is created by siphoning nature esshounds and shifters, requiring one rune essence and giving 43.5 and 86.8 experience respectively. This requires 44 Runecrafting.
Nature runes are worth 1.5 Runespan points and can be used to cross vine platforms and mist platforms. They can also be used to chip death esswraiths. They will disappear and be converted into points if you leave the Runespan.
If you try to bank any runes or essence from Runespan you get the message "A magical force prevents you from banking this item."