There are many different species of ragweed and there are three species that are very common in the United States. Ambrosia artemisiifolia L., Ambrosia psilostachya and Ambrosia trifida.
There is also great interest in preventing the spread of these plants because its pollen is a significant human allergen. It is one of the most familiar allergenic ragweeds, and residents of different regions begin to experience allergic symptoms as the plant spreads into the area.
Ambrosia artemisiifolia L.
Common Ragweed, is the most widespread plant of the genus Ambrosia in North America. It has also been called Annual Ragweed, Bitterweed, Blackweed, Carrot Weed, Hay Fever Weed, Roman Wormwood, Stammerwort, Stickweed, Tassel Weed, and American Wormwood. It is native in North America. The species name, artemisiifolia, is given because the leaves were thought to bear a resemblance to the leaves of Artemisia, the true wormwoods.
Common Ragweed grows to about one meter (3 feet) in height. Its wind-dispersed pollen is a strong allergen to many people with hay fever. Common Ragweed emerges in the late spring, and sets seed in later summer or fall.
It has become an invasive species in some European countries, and in Japan, where it is known as butakusa —pig grass.
Common ragweed is a very competitive weed and can produce yield losses in soybeans as high as 30%. Control with night tillage reduces emergence by around 45%. Small grains in rotation will also suppress common ragweed if they are overseeded with clover. Otherwise, the ragweed will grow and mature and produce seeds in the small grain stubble. Several herbicides are effective against common ragweed, although resistant populations are known to exist.
Common names include; Annual, Bitterweed, Blackweed, Carrot Weed, Hay Fever Weed, Roman Wormwood, Stammerwort, Stickweed, Tassel Weed, Wild Tansy, and American Wormwood. This ragweed will grow to be about 3 feet in height about knee high or less and has deeply cut “raggy” looking leaves as seen in the photo to your right.
Ambrosia psilostachya is an erect perennial herb growing a slender, branching, straw-colored stem to a maximum height near two meters, but more often remaining under one meter tall. Leaves are up to 12 centimeters long and vary in shape from lance-shaped to nearly oval, and they are divided into many narrow, pointed lobes. The stem and leaves are hairy.
The top of the stem is occupied by an inflorescence which is usually a spike. The species is monoecious, and the inflorescence is composed of staminate (male) flower heads with the pistillate heads located below and in the axils of leaves.
The pistillate heads yield fruits which are achenes located within oval-shaped greenish-brown burs about half a centimeter long. The burs are hairy and sometimes spiny. The plant reproduces by seed and by sprouting up from a creeping rhizome-like root system.
It is native to most of North America including all of southern Canada, nearly all of the continental United States, and the northern half of Mexico.
It is a common plant in many habitat types, including disturbed areas such as roadsides.
Common names include; Cuman, perennial, and western ragweed. It grows in the continental United States, the southern parts of Canada and the northern half of Mexico. It grows to be about one to two meters in height and offers leaves that are about 4 inches long.
Ambrosia trifida is a species of flowering plant in the aster family, Asteraceae. It is native to North America, where it is widespread in Canada, the United States, and northern Mexico. It is present in Europe and Asia as an introduced species, and it is known as a common weed in many regions.
This is an annual herb usually growing up to 2 meters tall, but known to reach 6 meters in rich, moist soils. The tough stems have woody bases and are branching or unbranched. Most leaves are oppositely arranged. The blades are variable in shape, sometimes palmate with five lobes, and often with toothed edges. The largest can be over 8 inches long by 7 inches wide. They are borne on petioles several centimeters long. They are glandular and rough in texture. The species is monoecious, with plants bearing inflorescences containing both pistillate and staminate flowers. The former are clustered at the base of the spike and the latter grow at the end. The fruit is a bur a few millimeters long tipped with several tiny spines.
Ambrosia trifida is the most competitive weeds in North America, where it is native. It grows to about 6 feet tall with green flowers and rounded leaves with 3 or 5 pointy-tipped lobes.
This species is well known as a noxious weed, both in its native range and in areas where it is an introduced and often invasive species. It is naturalized in some areas, and it is recorded as an adventive species in others. It grows in many types of disturbed habitat, such as roadsides, and in cultivated fields. Widespread seed dispersal occurs when its spiny burs fall off the plant and are carried to new habitat by people, animals, machinery, or flowing water. The plant is destructive to native and crop plants because it easily outcompetes them for light.
Common names include; , Buffalo Weed, Great, Giant, Bitterweed, Bloodweed, Horse Cane, and Tall Ambrosia.