The different types of root systems

Taproot system or taproot

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

The main root grows deep and vertically down into the soil, while lateral secondary roots develop from it. Taproots can take several forms: conical, like a carrot; fusiform, like a long radish; or napiform, like a turnip. Plants with this type of root system are difficult to pull out of the soil and to transplant. Over the course of evolution, many taproots have become modified into particularly efficient storage organs.

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

Taproot © Gwenaëlle David-Authier

The fasciculate root system

A root system more commonly found in monocotyledons, particularly grasses and bulbous plants.

A fibrous root system forms a bundle of roots that all emerge from the same point, so there is no main root. This can be seen very clearly when you pull up a tuft of grass, but it is also highly visible on leeks, whose roots all emerge from the base of the swollen stem (as a reminder, bulbs are swollen stems transformed into storage organs, so they are not roots, which emerge from underneath).

A few examples: leek, tulip, onion, grasses, maize, plantain…

Fibrous root system © Gwenaëlle David-Authier

The running root system

In this case, the main root is poorly developed, so the lateral roots will take over. These will grow horizontally at a shallow depth and regularly produce a sort of mini taproot. This is what makes certain groundcover plants so effective at quickly colonising a given area, but the same also applies to a few trees found in our regions.

A few examples: poplar, willow, bamboo, beech, ash and the Fabaceae (beans, peas, broad beans…).

Running root © Gwenaëlle David-Authier

Adventive roots

Often complementing a primary root system, adventive roots form on stems from a node. As soon as the stem touches the soil, roots appear and enable a second shoot to grow. However, adventive roots can also appear on the stems of certain plants, such as tomatoes and maize, above the “‘true’” root system, in a process that could be summed up as follows: “‘two root systems will be more effective than one!’”

A few examples: strawberry, mint, periwinkle…

Adventive root © Gwenaëlle David-Authier

More unusual root systems

• clinging roots: as in ivy or climbing Hydrangea, these are adventive roots that enable the plant to attach itself to a support (wall, tree…). They cannot absorb nutrients under any circumstances and are therefore never harmful to the supporting 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, roots can develop inside a hollow but still living tree. They take up the nutrients contained in the humus that forms there. The tree can then grow towards its centre and restore an internal layer of bark;
• “storage” roots: such as tuberised roots (tubercles) in lesser celandine or dahlia, as well as certain succulent roots that enable water storage;
  

  Tuberous root © Gwenaëlle David-Authier

   

• structural roots: such as stilt roots, adventive roots anchored in the soil (mangrove trees), or the buttress roots of kapok trees, which stabilise trees by extending up along the trunk. These two types of root enable trees to remain standing in very soft or very shallow soils (equatorial forest);
• pneumatophores: these are vertical roots that emerge from the water and ensure gaseous exchange, as is the case with many mangrove or marsh trees (for example, the bald cypress);
• haustorial roots: these are roots that enable them to “suck up” water and nutrients directly from the supporting plant. This occurs in parasitic or semi-parasitic plant species such as mistletoe.

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

Did you know?

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

Roots interact with the flora and fauna in the soil. Thus, some plants, such as fabaceae and alder, for example, are capable of fixing atmospheric nitrogen from the air thanks to bacteria present in their roots.

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