Different types of root systems

Taproot root system or taproot

Basically, it’s a carrot! This type of root system is found in many plants, notably among dicotyledons and gymnosperms (conifers, Cycas and Ginkgos).

The primary root penetrates deeply and vertically into soil, while lateral secondary roots develop from it. Taproots can take several shapes: conical like a carrot, fusiform like a long radish or napiform like a turnip. Plants with this type of root system are difficult to uproot and transplant. Many taproots have been modified through evolution to become particularly efficient storage organs.

Some examples: Tomato, carrot, parsnip, radish (yes, what we eat is simply a swollen taproot!), oak, hawthorn, pine, spruce, dandelion…

Taproot © Gwenaëlle David-Authier

Fascicular root system

Root system more common in monocotyledons, notably grasses and bulbous plants.

Fasciculate root system forms a vascular bundle of roots that all start from the same point, so there is no main root. This is very clear when pulling up a clump of grass but is also very visible on leeks, whose roots all arise from the base of the swollen stem (as a reminder, bulbs are swollen stems transformed into a storage organ, so they are not roots, which emerge from below).

Some examples: leek, tulip, onion, grasses, maize, plantain…

Fasciculate root © Gwenaëlle David-Authier

Running root system

In this case, the primary root is underdeveloped, so the lateral roots take over. These grow horizontally at shallow depth and, at regular intervals, form a kind of mini taproot. This is what makes some groundcover plants so effective at rapidly colonising a given area, but it also occurs in some trees in our regions.

Some examples: poplar, willow, bamboo, beech, ash, Fabaceae (beans, peas, broad beans…).

Running root © Gwenaëlle David-Authier

Adventive roots

Often complementary to a primary root system, adventive roots form on stems, arising from a node. As soon as a stem touches the soil, roots appear and allow a second shoot to grow. But adventive roots can also appear on the stem of some plants (tomato or maize, for example) above the “true” root system; from a viewpoint that could be summed up as: “two root systems will be more effective than one!“

Some examples: strawberry, mint, periwinkle…

Adventive root © Gwenaëlle David-Authier

More anecdotal root systems

• climbing roots : as in ivy or climbing Hydrangea, these are adventitious roots that allow the plant to attach to a support (wall, tree…). They do not absorb nutrients and are therefore never harmful to the host tree ;
• aerial roots : they develop on the vegetative part of the plant and are designed to absorb atmospheric moisture. They are found on tropical plants, especially epiphytes (orchids, bromeliads, Tillandsia…)  ;
• internal roots : surprisingly, inside a hollow but still living tree, roots can develop. They will take up nutrients from the humus formed there. The tree can then grow inward and restore an internal bark ;
• storage roots : like tuberised roots (tubercle) in lesser celandine or dahlia, or in some succulent roots that allow water storage ;
  

  Tuberous root © Gwenaëlle David-Authier

   

• structural roots : such as stilt roots, adventitious roots anchored in the soil (mangrove trees) or the buttress roots of kapok trees which, by extending up the trunk, stabilise trees. Both types of root help keep trees upright on very loose or very shallow soils (equatorial forest) ;
• respiratory roots : these are vertical roots that emerge from the water and ensure gas exchange as is the case for many mangrove or marsh trees (example: bald cypress) ;
• haustorial roots : these are roots that allow them to “suck” water and nutrients directly from the host plant. This is the case for parasitic or hemiparasitic species such as mistletoe.

Aerial roots of an orchid (photo: Gwenaëlle David), roots of a kapok tree at Cadiz botanical garden (photo: Gwenaëlle David), bamboo roots (photo: Ken Ishikawa)

Did you know?

In reality, some plants depending on species but also on external interactions (human activity, soil, climate, humidity…) can adopt mixed root systems that can be taproot, fasciculate or running root systems at the same time.

Roots interact with soil flora and fauna. Thus some plants, such as legumes and alder, are able to fix atmospheric nitrogen thanks to bacteria present in their roots.

Trees, but not only them, live in symbiosis with fungi, which allows them to exchange nutrients and even “communicate” with one another: these interfaces are called mycorrhizae. Everyone benefits from this association: fungus helps plant absorb water and certain minerals from soil, while plant supplies fungus with carbon that fungus cannot synthesise because it lacks photosynthesis.