One-flowered Cancer-root (Orobanche uniflora), also known as One-flowered Broomrape, produces up to five flowering stalks, each of which bears a single, fragrant, white-to-lavender flower. Glandular hairs cover the petals and two bright yellow ridges inside the flower may act as nectar guides for pollinating insects (although this flower does self-pollinate). One-flowered Cancer-root has no chlorophyll in the scale-like leaves that grow on its underground stem, and thus is incapable of making its own food. This parasitic plant is classified as a holoparasite – entirely dependent upon other host plants for its nutritional needs. These host plants often include Sedums as well as plants in the Saxifrage and Aster families.
The tiny One-flowered Cancer-root seedlings, with their limited food supply, must find a suitable host plant within a few days of germinating or die. The search for a host by One-flowered Cancer-root is guided by chemicals released by the growing roots of the host species. Once a host plant is located, the One-flowered Cancer-root’s root hairs exude an adhesive substance that attaches its roots to those of the host plant. Enzymes break down the cell walls of the host, and a tuber-like connection (haustorium) forms between the vascular tissue of the two plants, allowing the movement of water, minerals and carbohydrates to flow in one direction, from host to parasite.
Other species in the genus Orobanche are considered harmful as they parasitize crop plants, which One-flowered Cancer-root does not do. (Thanks to Shiela Swett for photo op.)
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