Parts of a Cactus

Everyone knows it is a plant, but what is a cactus exactly? These succulents have unique, exciting characteristics that set them apart from other flora, and they are associated with dry, arid regions, like deserts. There are 2,000 species with 139 genera, and the way they look, live and reproduce are all pretty fascinating.

Cacti have roots, and cacti roots are responsible for absorbing water and nutrients from the ground to provide them to the stem or trunk that is filled with thick, succulent vascular tissue. A neck connects the roots to the stem, which is how the water and nutrients travel there. Cacti also have areolas, which are spine and flower growth nodes that come in different shapes. Most are whitish to light brown and are round with hair, spines or thorns; these are the only spots on which the hair or thorns grow on the trunk.

Why does a cactus have thorns? These are actually modified leaves and function to direct water toward the trunk, prevent evaporation and protect the plant from herbivorous predators and the sun. These adaptations for a cactus help it survive and thrive in areas with bright sun and little water.

A cactus corona is its highest part and connects directly to the plant's vascular tissue. Cacti can also have small, medium or large flowers that can be white, yellow, pink, orange and red. Insects and bats pollinate these flowers.

The inside structure of these succulent plants varies depending on the species, but you can get a good idea by looking inside a giant saguaro cactus. In the middle of the trunk are woody ribs for stability; humans can use these ribs in the same ways as regular tree wood for crafting and building. There is spongy flesh (vascular tissue) around the ribs, and this is where the water and nutrients are stored. The tissue consists of thin-walled storage cells made up of gummy substances.

You can also see environmental adaptations for a cactus inside its root system. The roots may be tuberous, fleshy and thick or fibrous, made from connective tissue. Small and shallow, these are covered in corklike layers to retain moisture. The roots have absorbent, fine hairs on the outside; these are shed and replaced by new ones as the plant grows.

Like many other plants, cactus plants reproduce through their seeds. The colorful flowers are solitary for the most part. They consist of a floral tube and can have petal or leaflike structures. The floral tube is above a one-chambered ovary that is covered with pollen receptors (stigmas). Once fertilized, the ovary may evolve into a fruit. Most cacti fruits are berries with tiny seeds inside. After the ovary has become a fruit, the whole floral tube separates from the ovary and leaves a noticeable scar on the plant.

Other kinds of cacti reproduce at the ground level vegetatively by sprouting small plantlets; some can also reproduce via the process of fragmentation. This fragmentation is when segments break off from the central part and root to form clonal individuals. Interestingly, cacti tissues from different kinds of species are so compatible that scientists can graft part of one onto another species.