upper part of root or rhizome

例句：

1. 1. The tree's root system is extensive.
   这棵树的根系很发达。
2. 2. The roots of the plant are visible through the soil.
   植物的根系在土壤中可见。
3. 3. Root vegetables are rich in vitamins and minerals.
   根菜富含维生素和矿物质。