Jungle Burrs are seeds dropped by Rainforest Trees in the Hamlet DLC. They are only dropped during the Lush Season when the Rainforest Trees bloom and Strong Winds blow, or the trees are chopped down. Burrs can then be planted to grow into a new tree. They cannot be planted on Rocky Turf.
If a Jungle Burr is planted in the Gas RainforestBiome, it will grow a rotten version of Rainforest Tree instead of normal one.