Cuscuta warneri (Warner's Dodder)

Cuscuta warneri (Warner's Dodder)

Photograph by Mihai Costea, Digital Atlas of Cuscuta at (2007)
Scientific Name with Author
Cuscuta warneri Yuncker
Common Name
Warner's Dodder
Rare Plant Conservation Scorecard Summary
Overall Conservation Status Documented Threats Actions Needed

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Twining, tangled, yellow threadlike annual with stems 0.5 mm or less in diameter; inflorescence a glomerule of subsessile flowers on glabrous pedicels; flowers 5-merous, 2.1-4 mm long, slightly fleshy; calyx campanulate-cupulate, about 1/2 the corolla length, divided about 1/2 its length into triangular-ovate lobes, each apically enlarged to form a large, prominent, divergent, horn-like projection 0.5-0.75 mm long; corolla tube campanulate-urceolate, 1.7-2.5 mm long, the lobes triangular, more or less auriculate, acute, 0.5-0.7 mm long, 1/3-1/4 the corolla length, suberect, apically inflexed and basally overlapping; stamens included, incurved over the ovary; infrastaminal scales about reaching the filaments, united with the corolla tube for about 1/2 their length, oblong, shallowly and irregularly toothed at the truncate apex; styles distinct, 0.2-0.4 mm long, evenly filiform, barely longer than the collar-like stylopodium, the stigmas globose, capitate; capsules semi-transparent when dry, more or less papillose, globose, 0.9-1.2 mm long, indehiscent or irregularly dehiscent, enveloped by the corolla, the suture line between the two carpels not depressed, apical region of capsule thickened and raised around the style-base; seeds 2 per capsule. Flowers in September.
Similar Species
All dodders are superficially similar, appearing as yellow or yellow-orange piles of string on the vegetation. Cuscuta warneri has the following combination of characters that distinguishes it from other dodders: fleshy, papillose flowers, corolla lobes with inflexed tips, capsules with a thickened ring at apex, the styles short and the stigmas barely projecting beyond ring; calyx lobes with apical thickened spur-like projections; infrastaminal scales shallowly and irregularly toothed at truncate apex.
New Mexico, Sierra and Roosevelt counties; Utah, Millard County; possibly Arizona, Coconino County.
Grows on Phyla in open wet areas that support the host species; 1,430-1,460 m (4,700-4,800 ft).
Cuscuta warneri is sometimes considered an unnamed variety of Cuscuta indecora Choisy. Until recently, it was known with certainty from only two collections, one made in Utah in 1957 by Lloyd Warner, the other made in New Mexico in 1998 by Roger Peterson. Correll and Correll (1972) report it, Growing on Phyla cuneifolia about wet bank of a shallow pond in Arizona (Coconino County), but no vouchers for this locality exist in Arizona herbaria and Costea et al. (2006) who have studied the plant recently are unaware of vouchers that substantiate the report from northern Arizona. It has not been relocated in Utah, despite several searches in the vicinity of the type collection. All literature reports that C. warneri occurs on Phyla, but the specimen at NMC has the species parasitizing some unknown species of legume (the duplicate of this collection held by the collector, Roger Peterson, does have Phyla as the host). Spellenberg collected it at two localities in Roosevelt County in June, 2008. The specimens, confirmed by Costea, were growing on Phyla in a roadside ditch.
Conservation Considerations
Dodders (Cuscuta spp.) are serious pests of some crops and subject to eradication when they occur in or near agricultural fields. Attempts to identify the particular species being eradicated are almost never made. Almost nothing is known about the natural history of this species. Attempts should be made to relocate the Cuscuta warneri population in New Mexico to determine general habitat, hosts, frequency of plants and extent of the population. Similar habitats then should be searched.
Important Literature

Correll, D.S. and H.B. Correll. 1972. Aquatic and wetland plants of southwestern United States. U.S. Government Printing Office, Washington, DC.

*Costea, M., G.L. Nesom, S. Stefanović. 2006. Taxonomy of the Cuscuta indecora (Convolvulaceae) complex in North America. Sida 22:209-225. (Scanning electron micrographs of flower and capsule.)

*Yuncker, T.G. 1960. Two new species of Cuscuta from North America. Brittonia 12:38-40. (Line drawing of flower and capsule.)

Information Compiled By
Richard Spellenberg 2007, last updated 2008

For distribution maps and more information, visit Natural Heritage New Mexico