minecraft-assets/data/minecraft/recipes/muddy_mangrove_roots.json

{
  "type": "minecraft:crafting_shapeless",
  "category": "building",
  "ingredients": [
    {
      "item": "minecraft:mud"
    },
    {
      "item": "minecraft:mangrove_roots"
    }
  ],
  "result": {
    "item": "minecraft:muddy_mangrove_roots"
  }
}