“Wild rhubarb” generally refers to plants from the genus Rheum, specifically Rheum rhabarbarum, growing outside of a cultivated garden setting, often as feral escapees. These herbaceous perennials are known for their large leaves and fleshy leaf stalks, which emerge directly from a basal crown in the spring. Identification relies on several specific, observable characteristics of the plant’s structure.
Distinctive Physical Features
The appearance of wild rhubarb is dominated by its immense foliage, which forms a dense, low-lying clump. The leaves are large, often reaching up to two feet across, with a broad, heart-shaped, or sometimes triangular form. These substantial leaves have prominent veins and often feature a slightly ruffled or crinkled texture, though the surface is typically smooth.
The entire leaf structure arises from a thick, underground stem known as a rhizome. Each leaf is connected to the base by a long, fleshy stalk called a petiole. These petioles are the part of the plant consumed and vary in color from crimson-red to speckled pink or light green. The stalks are robust, often exceeding one inch in diameter and growing up to two feet long, with a distinctly concave or ‘U’-shaped groove running along the inner side.
Rhubarb is a robust perennial, with vegetative parts dying back in the autumn and regrowing each spring. Mature plants eventually send up a tall flower stalk, sometimes reaching five feet or more, bearing clusters of small, greenish-white to rose-red flowers. This flowering indicates the plant is “bolting,” which causes the edible stalks to become tougher and more bitter.
Edible Stalks Versus Toxic Leaves
The critical distinction in the rhubarb plant lies in the chemical composition of its different parts. The leaves are unsafe for consumption due to their high concentration of oxalic acid, a naturally occurring crystalline compound. Ingesting large quantities of this compound can lead to kidney damage or failure by binding with calcium in the body.
The rhubarb leaf blades contain oxalic acid ranging from 0.5% to 1.0% of their fresh weight. The stalks contain a much lower concentration, often about one-fifth the amount found in the leaves, making them safe to eat. The tart flavor of the stalks primarily comes from malic acid, not oxalic acid.
Some scientific debate suggests the leaves may contain an additional, unidentified toxin, possibly an anthraquinone glycoside. Due to the high oxalate content, always trim and discard the entire leaf blade before preparing the edible stalk. Frost-damaged stalks should also be avoided, as cold temperatures may cause some oxalic acid to migrate downward from the leaves.
Dangerous Plants Often Confused with Wild Rhubarb
Foraging for wild rhubarb carries risk because several highly toxic species share a similar growth habit, leading to dangerous misidentifications. One frequently confused plant is Common Burdock (Arctium minus), sometimes incorrectly referred to as “wild rhubarb.” Burdock features large leaves and a basal rosette similar to rhubarb, but key differences are easily observed.
Unlike the smooth texture of rhubarb leaves, Burdock leaves are woolly or hairy on the underside. Crucially, rhubarb stalks are solid and fleshy with a concave groove, while Burdock stalks are generally round and hollow. Furthermore, Burdock’s second-year growth produces thistle-like flowers and burs, a feature entirely absent in rhubarb.
Another dangerous look-alike, especially in certain regions, is False Hellebore (Veratrum viride), a highly poisonous plant. False Hellebore leaves are deeply pleated, forming distinct accordion-like folds running the length of the leaf. These leaves also grow in a tight spiral arrangement and wrap around the central stem. In contrast, each rhubarb leaf is attached to the crown by a separate, distinct petiole that does not wrap around a central stalk.