Friday, 27 March 2015

Dodder, a spiraling parasite

Dodder (Cuscuta and Grammica), is a twining yellow or orange plant sometimes tinged with purple or red. Occasionally it is almost white. Dodder can be identified by its thin stems appearing leafless, with the leaves reduced to minute scales.

Dodder is classified as a member of the Morning-Glory Family (Convolvulaceae) in older references, and as a member of the Dodder Family (Cuscutaceae) in the more recent publications. Dodder parasitizes various kinds of

wild and cultivated plants, and is especially destructive to alfalfa, lespedeza, flax, clover and potatoes. Ornamentals attacked included chrysanthemum, dahlia, helenium, Virginia-creeper, trumpet-vine, English ivy and petunias.

The seedlings must attach to a suitable host within a few days of germinating or they die. Once the Dodder seedling finds a host plant, it quickly twines itself around the plant's stem. Dodder always twines in a counter-clockwise direction. Next, Dodder will lose its connection to the ground. It now totally depends upon its host. The basal part of the parasite soon shrivels away so that no soil connection exists. Its water, minerals and carbohydrates are absorbed from the host through haustoria that press up against the stem of the host plant and penetrate the tissue. In dodder the haustoria are modified adventitious roots. Dodder rarely kills its host plant, although it will stunt its growth.

The flowers are numerous, white, pink or yellowish, small (2 to 4 mm long depending on species), and can be borne in tight balls or in a loose cluster (again depending on species). Flowers normally appear from early June to the end of the growing season. The fruit is about 3 mm in diameter, with thin papery walls and contain 1 to 4 seeds. The seeds are yellow to brown or black, nearly round and have a fine rough surface with one round and two flat sides. These seeds drop to the ground and germinate the next growing season if a suitable host is present. If no suitable host is present, the seed may remain dormant for five years.

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