rope dodder

not listed

NNR - Unranked

SNR - Unranked

not listed

FN – Federal noxious weed

RS – State restricted weed seed

Rope dodder is considered a noxious weed in the United States and a restricted weed seed in Minnesota, but is listed as threatened in Florida and is a Special Concern species in Wisconsin.

Rope dodder is an annual herbaceous vine that parasitizes the above-ground portion of other plants. In the spring a seed produces a single, slender, fast-growing stem, and a single root. The root is for anchoring only. It does not absorb nutrients and withers away after the stem attaches to a host plant. The stem lives solely on the nutrients stored in the embryo. It must find and attach to a host plant in 5 to 10 days or it will die. It seeks a compatible host by detecting and growing toward specific airborne volatile organic compounds. When it encounters another plant it wraps around it. If the plant is a suitable host the dodder stem will produce sucker-like, specialized roots (haustoria) that penetrate and draw nutrients from the host plant’s tissue. As it continues to grow it becomes more robust and climbs the host, twining in a counter-clockwise spiral.

The stems are wiry, branched, hairless, and yellowish-green, yellow, or orange. They are medium in diameter relative to other dodders but vary greatly in width, even on the same plant. They are mostly 1 ⁄64″ to 3 ⁄128″ (.4 to .6 mm) but may be up to 1 ⁄16″ (2 mm) in diameter. The stem sections between flower masses wither and fall away, often by flowering time.

The leaves are alternate, stalkless, scale-like, and 1 ⁄32″ to ⅛″ long. There is usually a single leaf subtending each node.

From May to early July rope dodder looks like orange tangled string. In July it produces flowers on parts of the stem that are tightly appressed. The inflorescence is a dense, rope-like mass of tiny flowers wound spirally around the stem of the host. The flowers are arranged in two parallel rows on opposite sides of the stem.

Each flower is subtended by several overlapping modified leaves (bracts). These floral bracts are yellowish at first, lance-shaped, and completely enclose the nascent flower. They are sharply pointed, boat-shaped, and bent backward and downward at the tip. After a few weeks the bracts turn white, the stem withers and falls away between inflorescences, and the flowers emerge above the bracts.

The flowers are stalkless and ⅛″ to 3 ⁄16″ long. They contain both male and female reproductive parts (perfect). They have 5 sepals, 5 petals, 5 stamens, and 2 styles. The sepals and petals are smooth, not hairy or bumpy. The sepals (calyx) are white and similar to the floral bracts but distinct, not fused together; sharply or bluntly pointed at the tip; and somewhat spreading at the tip but not bent backward. The petals are white, united at the base into a cylindrical corolla tube, and separated at the tip into 5 lobes. The lobes are shorter than the corolla tube, oblong to lance-shaped, sharply or bluntly pointed at the tip, and spreading or sometimes bent backward. The stamens are attached to the corolla tube below the lobes and are shorter than the lobes. They have white filaments and yellow anthers. Below each stamen a scale-like appendage (infrastaminal scale) is attached to the corolla tube. The infrastaminal scale is narrowly oval and densely fringed on the margin, profusely fringed at the top, less so along the sides. It is shorter than the corolla tube reaches the base of the filament. The anthers are about as long as or shorter than the filaments. The styles are slender; 3 ⁄64″ to ⅛″ long; distinct, not fused together; the same thickness throughout; and as long or longer than the ovary. At the tip of each style there is a head-like stigma. The stigma is not longer than thick.

The fruit is a flattened, globe-shaped, about ⅛″ thick capsule that may be more or less pointed at one end. It has paper-thin walls, a thickened collar and withered remnants of the corolla at the tip, and dried sepals at the base. When ripe it breaks open irregularly, not on a transverse circular line.

The seeds are light brown, oval, and 1 ⁄16″ to 5 ⁄64″long.

White

There are excellent microscopic photos of the tiny flowers at Iowa Plants.

Moist or wet. Prairies, sedge meadows, fens, roadside ditches, stream banks.

Mostly plants in the family Asteraceae, including Sunflower (Helianthus), goldenrod (Solidago), and ironweed (Vernonia), but also milkweed (Asclepias) and possibly mountain mint (Pycnanthemum).

July through September

Sources

2, 3, 4, 5, 7, 28, 29, 30.

Native

Rope dodder, Cuscuta glomerata

… rope dodder on Canada goldenrod, photographed on Barnes Prairie, Racine Co., WI Sept 3, 2017.

I haven't seen it on the prairie since then, but could have missed it.

Location: Barnes Prairie, Racine Co., WI

… rope dodder on Canada goldenrod, photographed on Barnes Prairie, Racine Co., WI Sept 3, 2017.

I haven't seen it on the prairie since then, but could have missed it.