Mosses and ferns both belong to the plant kingdom.
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Biological taxonomy term. 界 is the rank 'kingdom'. The full set: 动物界 (Animalia), 植物界 (Plantae), 真菌界 (Fungi), 原生生物界 (Protista), 原核生物界 (Monera). Don't confuse with the colloquial sense of 界 = 'world / circles' (e.g. 娱乐界, entertainment industry).
