Oxalis species, commonly known as wood sorrel or shamrock plants, are recognizable by their clover-like leaves and delicate flowers. While often sought after for their ornamental varieties, such as the purple-leafed Oxalis triangularis, many species are also persistent garden weeds. Understanding the nature of the underground storage structures is important for both successful cultivation and effective eradication.
Not All Oxalis Structures Are True Bulbs
The common assumption that Oxalis plants grow from true bulbs is botanically inaccurate. A true bulb, like an onion or tulip, consists of layers of fleshy scales surrounding a central growing point, which is not typical for this genus. Instead, Oxalis has evolved several specialized organs for perennation and energy storage, allowing the plant to survive unfavorable conditions and quickly regrow.
Many weedy species, such as creeping wood sorrel (Oxalis corniculata), rely on a network of fragile, slender rhizomes that spread laterally just beneath the soil surface. Other persistent varieties utilize small, segmented structures called bulbils, which are modified stem tissue that easily detach from the parent plant. Ornamental or edible species, like Oxalis tuberosa (oca), often develop starchy, thickened tuberous roots.
Visual Characteristics of Oxalis Storage Structures
The storage organs of weedy Oxalis are typically small and inconspicuous. The rhizomes of spreading species appear like thin, white to pale pink strings, often less than a few millimeters in diameter. These structures are notably fragile and snap easily when disturbed, aiding in their rapid proliferation throughout a garden bed.
The more problematic structures are the tiny, segmented bulbils produced by species like pink wood sorrel (Oxalis debilis). These resemble miniature white or pinkish-tan pinecones or stacked fish scales. They are usually less than one centimeter long and are covered in overlapping, fleshy segments that protect the growing point.
In contrast, the storage structures of cultivated Oxalis are substantially larger and more robust. The tuberous roots of Oxalis tuberosa, for example, are starchy and resemble small, elongated potatoes or carrots. These tubers can reach several inches in length and vary in color from pale yellow to deep purple or pink, depending on the variety.
The structures found on ornamental species, such as the rhizomes of Oxalis triangularis, are dark brown to black and form a cluster of scaly, elongated bodies, each about one to two inches long. Unlike the weedy counterparts, these organs are firm and designed to store substantial energy. This firmness makes them less prone to breaking apart during handling compared to the smaller, more fragile weed structures.
Location and Growth Habits
The location of these underground organs dictates the difficulty of their removal. Weedy Oxalis species typically position their fragile rhizomes and bulbils very close to the soil surface, often only one to three inches deep. This shallow positioning makes them easy to disturb with light weeding or cultivation.
Because these structures are so easily disturbed, tiny fragments are often left behind. Even a small segment of a rhizome or a single bulbil scale is capable of generating an entirely new plant, which is why hand-pulling weedy Oxalis can inadvertently worsen the infestation.
In contrast, the larger, starchy tuberous roots of cultivated species are generally found deeper within the soil profile. The substantial size of these organs necessitates a greater depth for proper development and anchorage, meaning they require more deliberate digging to harvest or relocate.