NOTE: The information on this page covers both noxious and non-noxious Cuscuta species (see below). All species of Cuscuta are regulated as plant pests under 7 CFR 330.
Fruit a round, 2-loculed capsule containing up to 4 seeds. Seeds variously shaped: round, ovate or obovate, to oblong in outline, and globose, subglobose, ovoid, or angular in three dimensions, may be flat or depressed on 1 or 2 sides; 0.5–5 mm long, with most ca. 1–2 mm long. Variously colored; from light gray, yellowish, or reddish, to dark brown. Surface finely to coarsely rough, granular, rugose, pitted, reticulate or scurfy. Scar area small, distinct, in the middle of which the hilum appears as a raised line, point or slit. Embryo linear, coiled, normal cotyledons lacking; endosperm hard and clear or semi-transparent.
nearly worldwide, with most of the species native to the New World from Canada to Argentina
a weed of cultivated and perennial crops, pastures, ditchbanks, roadsides
Cuscuta are usually annual, obligate parasites lacking chlorophyll. The stems twine around a host, producing haustoria that attach to the host stem and extract nutrients (unlike root parasites such as Striga and Orobanche). The genus comprises ca. 170 species. Some are specific to a few hosts, while some parasitize many species. The Cuscuta fruit matures at the same time as the host fruit, so the two are harvested together. Cuscuta seed contamination of crop seeds is very common, and is the major means of spread. Separation is difficult when Cuscuta seeds are the same size and shape as host seeds such as those of legumes. These parasites are common agricultural weeds throughout the world, causing reductions in yield of many crops and, if infestations are heavy, death of the host.
Selected agronomically important species that are federally noxious: C. australis R.Br., C. chinensis Lam., C. hyalina Roth., C. japonica Choisy, C. monogyna Vahl.
Some weedy species commonly found with crop seed that are not federally noxious: C. campestris Yuncker, C. cassytoides Nees ex Engelm., C. compacta Juss., C. epilinum Weihe, C. epithyum (L.) L., C. europea L., C. exaltata Engelm., C. gronovii Willd., C. indecora Choisy, C. pentagona Engelm., C. planiflora Ten., C. suaveolens Ser.
All Cuscuta are on the federal noxious weed list except the following, which are native to the U.S. or introduced and widespread (but note that all species of Cuscuta are regulated as plant pests and require a pest permit for importation or interstate movement):
C. americana L., C. applanta Engelm., C. approximata Bab., C. attenuata Waterfall, C. boldinghii Urb., C. brachycalyx (Yuncker) Yuncker, C. californica Hook. & Arn., C. campestris Yuncker, C. cassytoides Nees ex Engelm., C. ceanothii Behr, C. cephalanthii Engelm., C. compacta Juss., C. coryli Engelm., C. cuspidata Engelm., C. decipiens Yuncker, C. dentatasquamata Yuncker, C. denticulata Engelm., C. epilinum Weihe, C. epithymum (L.) L., C. erosa Yuncker, C. europaea L., C. exalta Engelm., C. fasciculata Yuncker, C. glabrior (Engelm.) Yuncker, C. globulosa Benth., C. glomerata Choisy, C. gronovii Willd., C. harperi Small, C. howelliana Rubtzoff, C. indecora Choisy, C. jepsonii Yuncker, C. leptantha Engelm., C. mitriformis Engelm., C. nevadensis I.M. Johnson, C. obtusifolia H.B.K., C. occidentalis Millsp. ex Mill. & Nutt., C. odontolepis Engelm., C. pentagona Engelm., C. planiflora Ten., C. plattensis A. Nels., C. polygonorum Engelm., C. rostrata Schutt. ex Engelm., C. runyonii Yuncker, C. salina Yuncker, C. sanwichiana Choisy, C. squamata Engelm., C. suaveolens Ser., C. suksdorfii Yuncker, C. tuberculata Brandeg., C. umbellata H.B.K., C. umbrosa Bey. ex Hook., C. vetchii Brandeg., C. warneri Yuncker.
Cuscuta australis A, seed; B, longitudinal section of seed showing embryo; C, transection of seed; drawing by Lynda E. Chandler