Taproot

A plant's taproot is a straight tapering root that grows vertically down. It forms a center from which other roots sprout.

Plants with taproots are difficult to transplant. The presence of a taproot is why dandelions are hard to uproot — the top is pulled, but the long taproot stays in the ground, and re-sprouts.

A taproot system contrasts to a fibrous root system with many branched roots.

Most trees begin life with a taproot, but after one to a few years the main root system changes to a wide-spreading fibrous root system with mainly horizontal growing surface roots and only a few vertical, deep anchoring roots. A typical mature tree 30–50 m tall has a root system that extends horizontally in all directions as far as the tree is tall or more, but well over 95% of the roots are in the top 50 cm depth of soil.

Many taproots are modified into storage organs.

Some plants with taproots:

*Burdock
*Dandelion
*Kudzu
*Parsnip
*Patterson's Curse
*Poppy mallow
*Radish
*Turnip
*Carrot
*Green alkanet
*Sturt's Desert Pea
*Welwitschia

Development

Taproots develop from the radicle of the seed, which forms the primary root. It produces branches called the secondary roots, and they in turn produce branches to form tertiary roots. These may further branch to form rootlets.

Typical taproots

*Conical root: this type root tuber is conical in shape, i.e. broad at the base and tapering gradually towards the apex: e.g. carrot.
*Fusiform root: this root is swollen in the middle and tapers towards the base and the apex: e.g. radish.
*Napiform root: the root has a top-like appearance. It is very broad at the base and tapers suddenly like a tail at the apex: e.g. turnip.

External links and references

* [http://www.sciencedaily.com/releases/2006/01/060112035906.htm 2006-01-13, Sciencedaily: Deep-rooted Plants Have Much Greater Impact On Climate Than Experts Thought] Citation: "…The tap roots transfer rainwater from the surface to reservoirs deep underground and redistribute water… increases photosynthesis and the evaporation of water… by 40 percent in the dry season… During the wet season, these plants can store as much as 10 percent of the annual precipitation as deep as 13 meters (43 feet) underground, to be tapped during the dry months… tree roots acting like pipes to allow water to shift around much faster than it could otherwise percolate through the soil."
* [http://www.hcs.ohio-state.edu/mg/manual/botany.htm Botany Manual] at Ohio State University.
* [http://www.arboretum.fullerton.edu/grow/taproot.asp Fullerton Arboretum on taproots]