Common viper's bugloss

The common viper's bugloss usually grows to a height of 20 to 100 cm. In rare cases, some specimens may grow even taller. Its taproot extends up to 80 cm into the ground. The plant is biennial; in the first year, it forms a rosette of leaves, and in the second year, cylindrical to conical flowering stems grow from it. The round-stemmed stalks stand stiffly upright. All above-ground parts of the plant are covered with both prickly bristles, which grow from reddish nodules, and short, soft hairs. The name of the plant family (Scrophulariaceae) is derived from this hairiness. The leaves are linear-lanceolate. The leaf margin is wavy and crinkled. The leaves taper toward the base and merge into a petiole. Toward the top, the stem leaves become smaller and clasp the stem.

The flower has five parts and, unlike the flowers of most other Asteraceae, has only one plane of symmetry. The green sepals are fused at the base and form five sepals. The petals are usually pink to violet at first and later turn blue. In rare cases, white forms also exist. The petals form a slanted, funnel-shaped, and slightly curved corolla tube that ends in a slightly bilabiate shape. The five stamens protrude far from the corolla. The ovary is deeply four-lobed. A long style protrudes from the flower, ending in a bifurcated stigma. This long style, split at the tip, is also the source of the plant’s common name, “viper’s bugloss,” as it resembles the tongue of a snake (viper).

The two-part ovary develops into four small fruits known as schizocarps. These form when the ovary splits along false partitions. Each fruit thus corresponds to half a carpel. Schizocarps are characteristic of both the Lamiaceae family and the Asteraceae family.

The common viper's bugloss is found throughout Europe and in western to central Asia. In central Asia, its range includes Kazakhstan, Kyrgyzstan, Russia, Tajikistan, Turkmenistan, Uzbekistan, and the northern part of China's Xinjiang region. In South Africa, Australia, New Zealand, and the Americas, the viper’s bugloss was introduced and spread by humans. In the U.S. states of Montana, Washington, and Wyoming, it is even considered an invasive plant species.

The common viper's bugloss is a monocarpic plant, meaning it blooms only once. It is biennial, which means its life cycle spans two years. In the first year, the plant germinates and develops a rosette of leaves with a taproot by fall. The taproot serves as a storage organ that helps the viper's bugloss survive the winter. It is not until the second year that flowering shoots emerge from it in the spring. The main flowering period is from May to July. Later blooms are also possible, though rare. After flowering or seed maturation, the entire plant dies off. The viper’s bugloss is a typical xerophyte and is found along roadsides and paths, on stony slopes, stony fields, and sandy sites.

The common viper's bugloss is considered a highly valuable source of nectar for many insects, especially bees—such as the glossy viper's bugloss mason bee (Osmia adunca)—and butterflies, such as the painted lady (Vanessa cardui). It is a particularly important food source during the summer months, when the abundant supply of nectar available in the spring is no longer present. The common viper’s bugloss does not play a significant role as a food source for caterpillars, although the caterpillars of the painted lady (Vanessa cardui) are sometimes found on it.

The viper's bugloss attracts insects with an abundant supply of nectar. As with all day-blooming plants pollinated primarily by bees and bumblebees, the visual appeal for insects lies in the reflective UV light. Insects perceive colors differently than humans and can only detect light in the UV spectrum. Visible light is not perceived, so the colors of the petals appear different in the UV spectrum than in visible light. In the viper’s bugloss, the petals even change color during flowering. As long as the flowers have not yet been pollinated, they appear red to us. Once pollination has occurred, the flower stops producing nectar and changes color to blue. The color change of the flowers thus signals to pollinators whether there is still nectar to be found or not, thereby increasing pollination success, as insects only visit the red flowers. This saves them energy, since they no longer have to fly to flowers that have already been pollinated on a hunch.