European Birthwort

Aristolochia clematitis

European Birthwort prefers warmer, low-elevation climes. This plant is most remarkable for the way it is pollinated: small flies are "taken hostage" in its flowers and are not released until the stamen has been fully stripped. The flies, now heavy with pollen, are then released in order to pollinate neighbouring flowers.

Birthwort is a perennial which grows from 30 to 70cm. A cross-section of the irregular, erect stem is blunt and quadrangular. Its leaves are heart-shaped with a tip towards the front and markedly stalked. Two to six of the yellow flowers are arranged on the axils. The flowers consist of a greenish globular base with a long yellow ray floret, ending in a large, spoon-like yellow lobe at the tip. The plant flowers from May to June. The fruit which follows is a walnut-sized capsule with many seeds.

The main range of the Birthwort lies in the Mediterranean area and Western Asia. In Austria, occurrence is limited to lower elevations and then rarely or sporadic at best. The Birthwort is not native to Vorarlberg. The plant may be found in riparian forests and in temperate areas such as banks and the edges of vineyards.

Endangerment and Conservation Status
The Birthwort is regionally vulnerable in the Rhine Valley, the northern foothills of the Alps, and in the Carinthian Basin and valley areas. Not local in Vorarlberg but introduced in Salzburg and Tyrol.

Ecological Characteristics
The Birthwort possesses a remarkable strategy which ensures that its flowers are pollinated by default. The perianth of the flower is wide above and like a tube below. Attracted by the scent of the flower (which is not attractive to humans at all, as it smells like rotting meat), flies enter into the tube of the flower and slide down the smooth interior surface. Stiff downward-pointing hairs turn the flower into a trap, making escape impossible. The hairs relax to allow passage of the insect only after it has been loaded with pollen. Then the "heavy" insect is allowed to pass, only to be trapped in the next neighbouring flower! There the insect pollinates the unfolded stigma and is trapped until the stamen ripens.

Special Characteristics
Although Birthwort is toxic to humans, it is an essential source of food for Southern Festoon caterpillars (Zerynthia polyxena). The range of this magnificent butterfly is mainly Southern and south Eastern Europe, like its fodder plant. Austria forms the northern boundary of its range, because Birthwort grows less and less frequently the farther north one goes.