Weeds

Ambrosia psylostachya DC. - Perennial Ragweed.

Synonyms.

Ambrosia glandulosa Scheele., A.hispida Torr., A.maritima L., A.lindheimeriana Scheele., A.peruviana DC., A.coronopifolia Forr. et Gray.

Systematic position.

Family Asteraceae (Compositae), genus Ambrosia L.

Biological group.

Summer-green perennial plant forming offshoots.

Morphology and biology.

Root system is well developed. It consists of main tap root and numerous horizontal lateral rhizomes, which generate new stalks. Stems are 3-105 cm high, upright, branched or unbranched, harshly pubescent with stiff, short hairs. Phyllotaxy is mostly opposite below, alternate above. Leaves are 5-12 cm in length, thickend, green or gray-green, sub-sessile or located occasionally on short-winged petioles, pinnate or pinnatilobate (rarely entire). Leaf margins are entire or sparsely serrate. Flower heads contain either male or female flowers, situating on different parts of the same plant. Male calathidial head is 2-5 mm in diameter, pedicellate or sub-sessile, with 5-25 (40) flowers. Heads are gathered in spicate inflorescence. Inflorescence is raceme, 7-15 cm in length, containing 50-100 flower heads. Involucre is campaniform and hirsutulous; corolla five-lobed and yellow. Female heads are 1-flowered, sessile, single. They are located either at base of male inflorescences, or in axils of the upper leaves. Corolla is absent, but there is involucre remaining at fruit. Fruit is achene in an outer coat. It is olive-brown, gray, or dark gray. Weight of 1000 fruits is 3.0-3.5. Achene obovate, 3 mm long and 2 mm broad, with a short blunt beak being about 0.6 mm long. Outer coat of achene is ligneous, with spines. Pappus absent. Reproduction by seeds and cloning (by root offsprings). The plant grows since May, blossoms since July. Seeds ripen in August. Morphological variability of A. psylostachya is probably related to the presence of a polyploid series in this species. A. psylostachya is very similar in appearance to A. artemisiifolia, but the former is a perennial plant with horizontal creeping roots, whereas the latter is annual plant. Perennial Ragweed is usually smaller plant; with rougher, less deeply lobed leaves; having blunt involucral spines or having no these spines.

Distribution.

The plant originates in North America. The general distribution includes North America (Canada, the USA, and Mexico), Europe (Belgium, Hungary, Germany, Denmark, Poland, Holland, Spain, France, and Sweden), and Australia. On the territory of the former USSR it is now distributed in the European part of the Russian Federation and in Central Asia (Kazakhstan). In the Russian Federation the centers of weed are located in 5 areas, i.e., Volgograd (60 hectares), Orenburg (114 hectares) and Samara (153 hectares) Regions, Stavropol Territory (210 hectares) and Bashkortostan (622 hectares).

Ecology.

Perennial ragweed frequently grows in crops, on fallow lands, meadows, pastures, and on garbage places. As against other species (A. artemisiifolia) it successfully competes to perennial grasses. Plant prefers good drained soils (sandy or crushed stone) in open habitats. Roots of weed are resistant to cold temperatures

Economic significance.

Perennial Ragweed is one of the most difficultly eradicable weeds, being included in lists of quarantine weeds in many countries. Weed is nocuous. It causes reduced productivity of cultures; quality of crop (and forages) also decreases, and efficiency of pastures weakens. The weed is not edible for cattle. Its pollen is an allergen, causing pollinosis. Control measures includes regular destroying of the weed rhizomes with the help of appropriate types of soil treatment and herbicides; avoiding contamination of sowing material or ground by seeds; mowing-off or pulling-up the weed before fructification.

Related references:

Bassett, I. J. & Crompton, C. W. 1975. The biology of Canadian weeds. 11. Ambrosia artemisiifolia L. and A. psylostachya DC. Can. J. Plant Sci. 55: 463-476.
Moskalenko, G.P. 2001. Quarantine weeds of Russia. Moscow: Rosgoskarantin,. 280 pp. (in Russian).
Nikitin, V.V. 1983. Weed plants of the USSR flora. Leningrad: Nauka. 454 pp. (in Russian).

© Kravchenko O.E.