Areoles beneath the sand. Roots of Opuntia arenaria

A habitat in loose sand

Opuntia arenaria (formerly also O. polyacantha var. arenaria) grows in deep, loose sands of the Rio Grande valley and around the Potrillo Mountains, on the USA–Mexico border. Its underground system includes long, relatively thick roots from which shoots can develop. In 2026, Gorelick and Beaudin described these organs using observations of living plants and stained sections. [Gorelick and Beaudin 2026][2-WWW]

An areole forming inside a root

An areole is a specialised cactus short shoot. On roots of O. arenaria, it begins inside the tissues. The developing structure breaks through the periderm, the secondary covering replacing the original epidermis. After emerging, it retains hairs and usually glochids. Areoles may occur singly or in denser clusters. [Gorelick and Beaudin 2026]

Glochids are small, barbed elements of armature familiar from above-ground prickly pear segments. In the roots described, they were accompanied by trichomes, or hairs. Persistent, long spines were not found. Formation of such an organised areole indicates activation of a shoot developmental programme within the root. [Gorelick and Beaudin 2026]

Anatomy reveals organ identity

Sections of the main root showed a multistranded primary xylem arrangement, termed polyarch, and a central pith. Lateral roots also had many xylem strands, but no distinct pith. This tissue arrangement identifies a root despite the presence of areoles. Morphological peculiarity and anatomical organisation occur together here. [Gorelick and Beaudin 2026]

Parenchyma fills much of the interior. Numerous cells contain mucilage, and calcium oxalate druses are also visible in the preparations. Mucilage is abundant in both main and lateral roots, making their tissues resemble a succulent stem in this respect. The authors emphasise the unusually strong expression of this trait in the taxon studied. [Gorelick and Beaudin 2026]

A shoot beginning growth underground

New shoots can grow from roots connected to the plant or detached from it. A documented specimen produced a shoot on a root lying 3.5 cm beneath the substrate surface while retaining its connection to the above-ground part. Development began before areoles at this site broke through the periderm. An underground position therefore does not prevent initiation of shoot growth. [Gorelick and Beaudin 2026]

Before replanting, the root was excavated and used to obtain sections. The observation describes the material's regenerative capacity after this procedure. Determining its role in natural population expansion requires measurements of offset numbers and survival in the habitat. The ability to initiate a new shoot beneath a still-intact root covering remains an important anatomical finding. [Gorelick and Beaudin 2026]

Functions of the underground part

The root of O. arenaria combines the structure of an uptake and transport organ with abundant parenchyma and the ability to form areoles. The physiological role of glochids in the sand has not yet been measured. Their presence raises a specific question about the conditions in which a root areole remains a short shoot and when it begins growth of a new segment. [Gorelick and Beaudin 2026]