Classification of plants is useful. Why Mushroom cannot be kept in the division algae. Why
A pea plant is kept in the class dicotyledon. Why
A mustard plant is placed under phanerogams. Why

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1) The word Fungi is itself a Latin word, which means "Mushroom." That's why mushroom is present in fungi group. Algae produce it's food by itself by the photosynthesis and are not parasitic.

2)A pea is a dicotyledonous plant, the seed (the pea itself) has two halves, cotyledons, hence dicot - di=2.

3)Those plants that bear flower and fruits after their maturity are called phanerogams. So mostly, they reproduce sexually. And mustard is the example if phanerogams.

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