Written Findings of the State Noxious Weed Control Board - Class A Weed
Spurge Flax (Thymelaea passerina (L.) Coss. & Germ.) FamilyFamily: Thymelaeaceae Description and VariationDescription and Variation: Spurge flax is an herbaceous annual with a fibrous taproot. The overall plant size ranges from 2 ½ inches to two feet tall. Slender, wiry and erect, spurge flax grows as one main stem, or more commonly, branches from the upper plant. The leaf arrangement is alternate. The small and narrow (8-14 mm long) linear shaped, leathery leaves taper to a point, and are progressively smaller upward along the stems. The leaves are sessile and jointed at a yellow cartilaginous base. The flowers are greenish and tubular, two to three mm long, perfect and incomplete: four sepals, no petals, and eight stamens. The stamens are in two whorls of four. Below each flower, two very small bracts arise from a tuft of tiny white hairs. The fruit is a shiny black achene. The round seeds are brown to black, two to three mm long. The plant turns red in the fall. This species is very tough to identify. Thymelaea passerina closely resembles Polygonum species - however there is no ocrea (papery sheath at the nodes). T. passerina is the only species in this genus, and it is the only herbaceous annual found in the Thymelaeaceae family. It is absent from many taxonomic keys, since only shrubby species were known in North America (Harriman 1979; Vincent and Thieret 1987). Economic ImportanceEconomic Importance: Detrimental: Spurge flax is mentioned as a common weed in central Europe and western Asia, where it shows up in grain crops. In Okanogan County, Washington, spurge flax covered 600 acres of native range land before it was noticed and identified. Animals will not graze this plant. Beneficial: None known HabitatHabitat: In Okanogan County, the only known Washington location, it is reported from steep, horse range land, growing near an alkaline lake in strong lime soil. Associated species include diffuse knapweed (Centaurea diffusa), common silverweed (Potentilla anserina), and sagebrush (Artemisia tridentata). In the midwest, spurge flax is described as a weed of disturbed places, found in dry pastures, bluffs, railroad embankments, and flood plains. In its native Eurasia, it is considered a common weed. Geographic DistributionGeographic Distribution: Spurge flax is native to Eurasia where it is considered a common weed of dry soils and grain fields of south and central Europe and western Asia (Pohl 1955). It is also found in central Russia, Australia, and North America (Vincent and Thieret 1987). Spurge flax is found in the Midwestern states of Ohio, Illinois, Iowa, Kansas, Mississippi, Nebraska, Wisconsin. It was first identified in Washington in 1996. HistoryHistory: Spurge flax seeds were probably introduced to North America as a feed seed contaminant (Vincent and Thieret 1987). Washington State University has an herbarium specimen, dated 1954, from Iowa. The Okanogan County Noxious Weed Control Board responded to a landowner request for identification in the fall of 1996, when he noticed this species growing in native horse range. The estimated infestation site covered about 600 acres, with a condensed infestation size estimate of 6 acres. An aggressive control program was initiated. Growth and DevelopmentGrowth and Development: Spurge flax is an annual. The literature mentions flowering times beginning as early as April with fruit production until frost. ReproductionReproduction: Spurge flax reproduces by seeds. Non apomictic. Pollinators unknown (Vincent and Thierat 1987). Birds may be a vector. Response to HerbicidesResponse to Herbicides: Spurge flax is difficult to control due to the lack of surface area of the small, leathery leaves. Okanogan County does have control plots in place, and will provide information as it becomes available. Response to Cultural MethodsResponse to Cultural Methods: Not known. Response to Mechanical MethodsResponse to Mechanical Methods: Not known. Biocontrol PotentialsBiocontrol Potentials: None known. Rationale for Listing: Thymelaea passerina, or spurge flax, is aggressive, it is very difficult to control, livestock will not graze this plant, and at this time the distribution is limited to Okanogan County. This weedy Eurasian species was not previously known to Washington state, nor any other Pacific Northwest site, prior to the fall of 1996. Spurge flax has an estimated infestation size of about 600 acres of native range land, with a condensed infestation size estimate of 6 acres. An aggressive control program makes control, and possibly eradication, feasible at this time. The Okanogan County Noxious Weed Control Board requested that spurge flax be listed as a noxious weed. References: George, V. and A. K. Rishi. 1982. Constituents of Thymelaea passerina. Fitoterapia. 1982. Vol. 53 (5/6). Pp. 191-2. Gleason, H.A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden. Bronx, NY. P. 312. Harriman, N.A. 1979. Four Additions to the Wisconsin Flora. The Michigan Botanist. Vol. 18 (4). Pp. 143145. McGregor, R.L. and T.M. Barkley, R. E. Brooks, E.K. Schofield. 1986. Flora of the Great Plains. University Press of Kansas. P. 498. Pohl, R. W. 1955. Thymelaea passerina, a new weed in the United States. Iowa Academy of Sciences, Vol. 62. Dec. 15, 1955. Tan, K. 1980. Studies in the Thymelaeaceae II: A revision of the genus Thymelaea. Notes Royal Bot. Gard. Edinburge 38: 189-246. Vincent, M.A. and J. W. Thieret. 1987. Thymelaea passerina (Thymelaeaceae) in Ohio. SIDA: Contributions to Botany. Vol. 12 (1). Pp. 75-78. Wofford, B.E. and H.R. De Selm. 1988. Distribution of and first report of Thymelaea passerina from the southeastern United States. Castanea. Dec 1988. Vol. 53 (4). Pp. 305-6. |