Weeds
Cyclachaena xanthiifolia (Nutt.) Fresen. - Rag Sumpweed, Burweed Marsh-Elder, False Ragweed.
Systematic position.
Family Asteraceae, genus Cyclachaena L.Synonym.
Iva xanthiifolia Nutt.Biological group.
Annual, late summer weed.Morphology and biology.
Stalk 30 to 200 cm in height, straight, costate, glabrous in lower part, pubescent in upper part. Leaves 4.5-10 mm in length, 3-6.5 mm in width, mainly opposite (except for the uppermost ones), petiolar, narrowing basad, pointed cordate-ovate at top, serrate-dentate along margins, rough owing to bristly hairs. Capitula numerous, heterogamous, 2-4 mm in diameter, drooping, aggregated in large, friable paniculate inflorescences located on the top of shoots or in sinuses of the upper leaves. Involucre semiglobular, oblate, consisting of 10 leaflets in two rows. Outer leaflets obovate, slightly pointed, grassy, pubescent, with long glandular hairs along margin. Inner leaflets glumaceous, bare, widely-obovate, truncated at top, strongly concave, densely surrounding pistillate flowers at hemicarps maturing. Receptacle flat, almost glabrous, with two or three fine pellicles. Five marginal pistillate flowers are fertile, with reduced ring-shaped perianth. 10-15 median flowers are androgynous, with pentadentate corolla, with underdeveloped pistil and almost free anthers, sterile. Corolla pale-greenish or yellowish-green. Hemicarps 2-3 mm in length and 1.2-1.5 mm in width, elongate-obovate or cuneate, slightly oblate; at top they are rounded, with 4 not distinctly projecting ribs, without pappus, dark brown. Blossoming in July - September. Reproduction by seeds. Sprouting from depth of no more than 6-8 cm, germinating capacity in soil is kept to 6 years. Freshly matured seeds do not sprout. The maximal fertility is 1790 thousand hemicarps. A major factor of C. xantifolia invasion is transportation of cargoes and vegetables collected from kitchen gardens, melon fields, and tilled fields, whence fine hemicarps can easily get in boxes, sack tare, straw and another packing material.Distribution.
Northern and Southern America, the Western Europe, Asia Minor, Japan, China, Australia.Ecology.
Prefers damp enough, friable and fertile soils. Minimal temperature for germinations of seeds is +2 - +3°C, optimum +12 - 20°C, maximum +34 - 36°C.Economic significance.
Litters tilled crops mainly, strongly exhausts and smothers crops, reducing yield by 40-80% and more. Control measures include removing of stubble, autumn plowing, presowing treatment of soil, cleaning of seed grain, interrow treatments, complete summer mowing of plants before hemicarps maturing, herbicides use if necessary.Related references:
Geideman, T.S. & Nikolaeva, L.P. 1954. On Distribution of some quarantine weeds in Moldavian SSR. In: News of Moldavian branch of AS of the USSR. Kishinev: State publishing House of Moldova 1(15): p. 59-64 (in Russian).Komarov, V.L., ed. 1959. Flora of the USSR. Moscow & Leningrad: AN SSSR. V. 25, p. 557-558 (in Russian).
Ul'yanova, T.N. 1998. Weed plants in the flora of Russia and other FSU countries. St. Petersburg: VIR. 233 p. (in Russian).