Ersi, Mother of Thorns is a Wild Harvest boss.
Wild Thornfruit is a Tier 4 Harvest Seed. When harvesting the seed, it will spawn the boss Ersi, Mother of Thorns.
While growing a tier 4 seed is difficult, defeating Ersi, Mother of Thorns is easy.
HHC 3.11 Wild Boss Ersi, Mother of Thorns