Common viper's bugloss

The common viper's bugloss usually reaches heights of 20 to 100 cm. Rarely, some specimens can grow even taller. Its taproot reaches up to 80 cm deep into the soil. The plant is biennial; in the first year, a leaf rosette forms, and in the second year, cylindrical to cone-shaped flowering shoots grow from it. The round stems stand stiffly upright. All above-ground parts of the plant are covered with both stinging bristly hairs growing from reddish tubercles and short soft hairs. The name of the plant family (Boraginaceae) is derived from this hairiness. The leaves are linear-lanceolate. The leaf margin is wavy and crinkled. The leaves narrow toward the base and transition into a petiole. Higher up, the stem leaves become smaller and stem-clasping.

The flower is pentamerous and, unlike the flowers of most other borage plants, has only one plane of symmetry. The green sepals are fused at the base and form 5 calyx lobes. The petals are usually pink to violet at first and later turn blue. In rare cases, white forms also occur. The petals form an obliquely funnel-shaped and slightly curved corolla tube that ends in a slightly two-lipped shape. The five stamens protrude far out of the corolla. The ovary is deeply four-lobed. A long style protrudes from the flower, ending in a two-forked stigma. This long, end-split style is also what gives the viper's bugloss its name, as it resembles the tongue of a snake (viper).

From the two-part ovary, four nutlets develop, known as eremuri. These form because the ovary divides along false partitions. A fruit thus corresponds to half a carpel. Nutlet fruits are characteristic of both the mint family and the borage family.

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

Viper's bugloss is a monocarpic plant, meaning it flowers only once. It is biennial, which means it has a two-year life cycle. In the first year, the plant germinates and forms a rosette of leaves with a taproot by autumn. The taproot serves as a storage organ that allows the viper's bugloss to survive the winter. Only in the second year do the flowering shoots emerge from it in the spring. The main flowering period is from May to July. Later flowers are occasionally possible. After flowering and seed maturation, the entire plant dies off. Viper's bugloss is a typical dry-habitat plant and can be found along roadsides, path edges, stony embankments, stony rough grasslands, and sandy locations.

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 daytime-blooming plants pollinated primarily by bees and bumblebees, the visual stimulus for insects is reflecting UV light. Insects see colors differently than we humans do and can only perceive light in the UV range. Visible light is not perceived, so the colors of the petals appear different in the UV range than in visible light. In the viper's bugloss, a color change of the petals even takes place during blooming. As long as the flowers are not yet pollinated, they appear red to us. Once pollination has taken place, the flower stops producing nectar and changes its color to blue. The color change of the flowers thus signals to floral visitors whether there is still nectar to be had or not, thereby increasing pollination success, as insects only fly to the red flowers. This saves them energy since they no longer have to visit already pollinated flowers on the off chance.