Rhubarb is a distinct plant, botanically classified as a vegetable, but its common culinary use in desserts often leads to it being treated as a fruit. This herbaceous perennial is grown for its fleshy leaf stalks, which possess a tart flavor. To understand how to identify and use this plant, it is important to focus on its physical structure, including its stalks, leaves, and overall growth habit.
The Stalks
The edible part of the rhubarb plant is the stalk, technically known as the petiole, which connects the leaf blade to the base of the plant. These petioles have a firm, crisp texture when fresh, but they can become somewhat stringy in older or over-mature plants. Their shape is generally thick and succulent, often described as triangular or celery-like.
The most striking feature of the stalks is their color, which can vary significantly even within the same patch. Stalks range from deep crimson or ruby red to speckled pink, or even a uniform bright green. This color is due to the presence of anthocyanins and is not a reliable indicator of ripeness, sweetness, or flavor.
Cultivars like ‘Valentine’ are known for their broad, deep red stalks. The color is often influenced by both the specific variety and the growing conditions, such as forcing the rhubarb in a dark environment. When harvested, the fresh stalks should be firm and glossy, with a noticeable tartness that makes them suitable for cooking.
The Leaves and Toxicity
The leaf blades of the rhubarb plant are remarkably large, often reaching up to 2 feet across on a mature plant. They are typically broad, shield-shaped, or heart-shaped with deep lobes. They feature a heavily crinkled or deeply veined surface texture, making them a prominent visual feature.
A crucial point of identification is that the leaves are toxic and should never be consumed by humans or pets. Their toxicity is primarily attributed to a high concentration of oxalic acid, a naturally occurring substance. Rhubarb leaves contain a much higher level of oxalic acid than the stalks. Consuming the leaves can cause mild symptoms like vomiting, and ingestion of a large amount can lead to serious issues, including kidney failure. Therefore, the large leaf blades must be completely trimmed off and discarded to ensure safety.
Growth Habit and Overall Structure
Rhubarb is a hardy herbaceous perennial, meaning its foliage dies back to the ground each winter, and new growth emerges from an underground structure called the crown in early spring. The plant is characterized by a bold, architectural appearance, quickly forming a large, imposing clump that can spread 5 feet or more in width. The leaves and stalks emerge directly from the crown.
A mature plant develops a substantial underground storage organ, or rhizome, which fuels the vigorous spring growth. During the growing season, a large central flower stalk may appear, rising above the foliage. This stalk is thick and upright, bearing numerous small, greenish-white to rose-red flowers. Gardeners often remove this flower stalk to redirect the plant’s energy back into producing more edible leaf stalks.