Dodder (Cuscuta spp.) doesn’t look much like a typical plant. A sprawling vine with yellow-orange, spaghetti-like stems, it seems to lack both leaves and flowers.
Actually, its leaves are reduced to tiny scales, and the flowers, when present, are small, pale, and bell-shaped.
Dodder is a parasite, and it grows in tangles on top of other plants. Worldwide, there are over a hundred species, particularly in subtropical and tropical regions.
Typical habitats include marshes, fields, and roadsides, where dodder may be more conspicuous than its host plants underneath. Several species are native to South Carolina, including C. gronovii, also called scaldweed.
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Dodder reproduces via tiny, hard-coated seeds that may stay viable for over 20 years.
Once sprouted, the seeds give rise to tiny seedlings that start life rooted in the soil and quickly exhibit a twining growth form. Since the seedlings can make little to no food on their own, they’ll die if they don’t attach to a host plant within 5-10 days of germination.
One study suggests that seedlings may locate potential hosts at least partly by orienting towards volatile, airborne substances emitted by certain plants. If this is true, just how dodder “smells” its hosts is unknown.
Once a seedling locates a suitable plant, it soon entwines itself around its host and the original roots of the dodder die. With time, the stems of a single dodder may envelop other nearby plants, stealing their nutrients via specialized knoblike structures that penetrate deep within the hosts’ tissues.
Dense growths of dodder on a plant may slow its growth rate and also weaken it, increasing its susceptibility to disease. Severe infestations can sometimes be deadly.
A wide variety of plants may serve as hosts for dodder, including potatoes, tomatoes, alfalfa, clover, flax, and chrysanthemums. Some dodders are relatively host-specific; other species, less so.
Of recent concern is the spread of Japanese dodder (C. japonica), a non-native species that has become a pest in parts of the southeastern United States.
Vicky McMillan, a retired biologist formerly at Colgate University,lives on Hilton Head Island. She can be reached at email@example.com.
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