Tap root are modified mainly for storage of food. They are known as tubers.  Based on shape tap root tubers are classified into four groups.
a) Fusiform tubers: A swollen root tapering at both ends is called fusiform.
fusiform- radish Example: Radish (Raphanus sativus)
b) Napiform tubers: The root is globular and tapers abruptly at the base.
Napiform- beet root Example: Beet root (Beet vulgaris), Turnip (Brassica campestris)
c) Conical tubers: The root is broad at the top and tapers towards the lower end like a cone.
Conical - Carrot Example: Carrot (Daucus carota)
d) Tuberous roots: The root is thick and fleshy. It has no definite shape.
Tuberous roots- Mirabilis jalapa

Example: 4 o’ clock plant (Mirabilis jalapa)
See also: Adventitious roots tubers
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