What is the distinguishing characteristic of spurges?

The defining feature of spurges is their production of a milky, acrid, irritating sap. This sap is a significant characteristic of the Euphorbiaceae family, to which spurges belong. It serves various purposes, including deterring herbivores due to its unpleasant taste and potential toxicity. This sap can cause skin irritation in sensitive individuals, making it an important identification trait for these plants.

The other options do not accurately capture the essence of spurges. Many spurges do not produce brightly colored flowers; instead, their flowers are often small and inconspicuous. While some species may have deep roots, this is not universally true for all spurges, and they are not primarily noted for this trait. Additionally, spurges are not specifically known for thriving in wet conditions; they can often be found in a range of habitats and are particularly adaptable to various soil types and moisture levels. Thus, the unique sap is the key reason why this characteristic stands out for the classification of spurges.