Cuscuta epithymum

Cuscuta epithymum
Dodder parasitizing gorse (Ulex europaeus)
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Solanales
Family:	Convolvulaceae
Genus:	Cuscuta
Species:	C. epithymum
Binomial name
Cuscuta epithymum (L.) L.
Synonyms
Lepimenes epithymum (L.) Raf. Cuscuta europaea var. epithymum L.

Cuscuta epithymum (dodder, lesser dodder, hellweed, strangle-tare) is a parasitic plant assigned to the family Cuscutaceae or Convolvulaceae, depending on the taxonomy. It is red-pigmented, not being photosynthetically active. It has a filiform habit, like a group of yarns. Its leaves are very small, like flakes. Its flowers, disposed in little glomerules, have a white corolla, with the androecium welded to the corolla.

In Eurasia, this species of dodder would often attach itself to the Conehead thyme (Thymus capitatus), taking on the plant's pungency and from whence it also derived its host's Arabic name, al-ṣaʿitrah. During medieval times, dodder was often used as a medicinal cure in treating depression, but causes thirst and dryness of the mouth when consumed.

Description

C.epithymum is a rootless holoparasitic plant. It has thin (0.25–0.40 mm) hairless filiform (thread-like) stems that are pink, red, yellow or purple. Its leaves are very small and scale-like on the stems. It attaches to the host plant via haustoria. The flowers are white or pink in groups of 7–25, growing directly on the stems. The flowers have five petals and sepals. The petals are joined together forming a cup-like corolla, which is longer than the sepals. The flowers are replaced by small round fruits topped with withered petals. The fruits contain up to four seeds, each about 1 mm long.

Distribution

As a native species C.epithymum occurs from Macaronesia in the west throughout most of Europe to as far east as Xinjiang in Northwest China. It is also present in parts of western North Africa. The species does not grow at higher altitudes.

Invasive species

C.epithymum has been unintentionally introduced into North and South America, Southern Africa, Australia, New Zealand and Primorsky Krai (southeastern Russia). Such introductions probably occurred due the import of contaminated seed from crops that it parasitizes, such as alfalfa.

Host species

C.epithymum parasitizes a wide range of plant species. In Hungary alone it has 391 different host species, 191 of which it was the only Cuscuta species to parasitize. The commonest (>20% affected) host plants are Achillea millefolium (Yarrow), Galium verum (Lady's bedstraw), Arrhenatherum elatius (False oat grass), Plantago lanceolata (Ribwort plantain), Lotus corniculatus (Bird's foot trefoil), Sanguisorba minor (Salad burnet), Festuca rupicola (Furrowed fescue), Teucrium chamaedrys (Wall germander), Daucus carota (Wild carrot) and Convolvulus arvensis (Field bindweed). In northwestern Europe the main host species are dry heathland species such as Ulex europaeus (Gorse), Clover and Calluna vulgaris (Common heather). In Spain it parasitizes Hormathophylla spinosa (Spiny madwort).

Life cycle

C.epithymum is generally regarded as annual and grows from seeds that germinate when conditions are right. The seeds have evidence of both physiological and physical dormancy, allowing them to survive in the soil for several years. Shoots must find a host plant quickly as the seed contains only minimal nutrition. Once the shoot has found a host plant it quickly climbs over it, twisting in a counter-clockwise fashion around the host stems. It then tightens and sends out haustoria that penetrate through the epidermis into the underlying xylem, allowing the parasite to draw both water and nutrients from the host. The stems of the parasite are tightly coiled around the host while other stems remain loosely coiled, allowing them to seek out other parts of the host or a new host. The plant flowers and is either pollinated by insects or, if necessary, is self-pollinated. The seeds are dispersed on the ground beneath the host to await future germination. On some perennial hosts it forms small galls, where parasitic tissue can survive the winter.

External links

• Media related to Cuscuta epithymum at Wikimedia Commons
• Data related to Cuscuta epithymum at Wikispecies