Helianthus lenticularis Dougl. ex Lindl. - Showy Sunflower.
Systematic position.Family Asteraceae, genus Helianthus L.
Synonyms.Helianthus annuus L., Helianthus annuus subsp. lenticularis (Dougl. ex Lindl.)
Biological group.Early annual spring weed.
Morphology and biology.Plant is 40-180 cm in height. Root stalky, deeply penetrating ground, with strongly ramified lateral roots. The stalk is straight, round, rigid, strongly ramified, forming branches of the second, third and fourth order. Leaves long-petiolate; lower leaves opposite, upper ones alternate, oval or cordate, full or serrulate, pubescent above and below. The whole plant has stiff pubescence with a violet tint. Receptacle highly convex. Marginal flowers lingular, yellow, asexual; inner ones tubular, bisexual, red-purple. Bracts scarious, three-apicate; all three rachides pointed; the median one is much longer. Involucres biseriate, broadly oval at base, sharply pointed at apex. Anthodia is 1-15 cm in diameter, numerous, fine, equal in size. One plant can bear up to 200 anthodia, having no main one. Hemicarp oval, poorly costate, frequently pubescent, 2-8 mm in length, 1.8-5 mm in width. Hemicarp coloring varies widely from light gray to black, with characteristic spottiness and mottling (except for longitudinal stripes). Weight of 1000 seeds is 27 g. Blossoming occurs in July-September. Reproduction occurs by seeds. The maximum fertility is 19,000 hemicarps. Shoots of the weed and spring wheat appear simultaneously. The growth and development of the weed is suppressed in thickened crops; it branches weakly, reaching only 20-30 cm in height.
Distribution.The European region of the former USSR, Western and Eastern Siberia, the Far East, Central Asia, USA, Canada, Mexico, and South America.
Ecology.The weed is drought-resistant and tolerant to various growth conditions. It develops especially strongly in humid places and on sites fertilized plentifully with organic fertilizers. Most seeds sprout at depths of 5-10 cm, though some sprout at depths of 15-20 cm. The minimum temperature for seed germination is +4-6°C. The weed has a short vegetation period (80-120 days). Fresh, ripe seeds do not sprout in autumn, as they have a long dormant period. Biological maturity of seeds occurs in 184-305 days. In the ground, they lose their germinating capacity after 2-3 years. Cut weed is able to grow due to formation of lateral sprouts.
Economic significance.Weed of grain, tilled, and vegetable crops; less often found in winter rye and perennial grasses. Causes the greatest harm in summer grain cereals. The Showy Sunflower sprouts simultaneously with summer wheat, overtaking the latter in growth, drying and exhausting soil, which results in significant reduction in crop yield; mass weediness results in complete destruction of crops. The work of harvesters is also deteriorated. The seeds litter both yield and the ground. Control measures include rotation with black and early fallows, with rye and vetch-oat mixture for green forage harvested before sunflower flowering and ripening; deep autumn plowing with closing weed seeds at depths of 25 cm or more with the use of colters; double cultivation of fields that exhibit high weediness, the first in early spring and the second just before sowing of late cultures in order to eradicate emerging shoots; cleaning of sowing material; cutting of weeds along roads, field edges, etc. before the Showy Sunflower flowers; tgimely harvesting; and the use of herbicides, if necessary.
Related references.Chepelev, R.D. 1977. Weeds of the Amur Region. Blagoveshchensk: Khabarovsk publishing house. 72 pp. (In Russian)
Nikitin, V.V. 1983. Weeds in the flora of the USSR. Leningrad: Nauka. 454 pp. (In Russian)
Veselovs.kii, I.V., Lisenko, A.K., Man.ko, Yu.P. 1988. Atlas-synopsis of weeds. Kyiv: Urozhai. 64 pp. (In Ukrainian)
Vizgin, V.A., ed. 1961. Instructions on the Showy Sunflower control. Moscow: Sel.khozizdat. 16 pp. (In Russian)