taproot

1. (botany) A long, tapering root, exhibited by many plant species (such as carrots and dandelions).Examples: "The taproots of trees like the false acacia, growing between Park Royal and Alperton, thrust deeply into the ground, while the spreading roots of the silver birch stitch the soil."; "Above the lower headcut, phreatophytic mesquite and little leaf sumac hug the banks, drawing pendulate water from the silts remaining from former marsh deposits and sending long taproots into channel stores."; "On the other hand, those who are compelled by a single strong desire are obsessed with a well-defined problem, which touches the taproot of their soul. They are on the attack, on the move."