Most hay fever sufferers dread summer. Pollen from various plants aggravates their allergies. Some of the worst pollen comes from the Ragweed (Genus Ambrosia). There are 2 species of Ragweed in this area: Common Ragweed (Ambrosia artemisiifolia L.) and Giant Ragweed (Ambrosia trifida L.). These 2 species can hybridize.
Ragweed is a member of the Order Asterales, the Family Asteraceae or Compositae, the Subfamily Asteroideae, and the Tribe Heliantheae. Ragweed was formerly in the Family Ambrosiaceae.
The generic name, Ambrosia, is Greek for “immortal” or “food of the gods”. It was believed that if mortals ate this food, they would become immortal. The specific epithet, artemsiifolia, is Latin for “with a leaf of the Wormwood (Genus Artemisia)”, which is another plant species. The specific epithet, trifida, is Latin for “3-cleft” or “3-lobed”, which is from the 3 lobes of the leaves.
Previous scientific synonyms for Common Ragweed were Ambrosia elatior L., A. glandulosa Scheele, A. maritima L., A. monophylla (Walter) Rydberg, and A. paniculata Michaux. A previous scientific synonym for Giant Ragweed was Ambrosia aptera de Candolle.
The common name, Ragweed, is from its ragged leaf patterns. Other common names for the Common Ragweed are Annual Bur-sage, Annual Ragweed, Bastard Wormwood, Bitterweed, Blackweed, Carrot Weed, Conot Weed, Hayfever Weed, Hayweed, Hogweed, Low Ragweed, Oxtail, Roman Wormwood, Short Ragweed, Small Ragweed, Stammerwort, Stickweed, Tassel Weed, Wild Tansy, and Wild Wormwood. Other common names for the Giant Ragweed are Bitterweed, Blood Ragweed, Bloodweed, Buffalo Weed, Great Ragweed, Hayfever Weed, Horsecane, Horseweed, King Head, Palmate Ragweed, Richweed, Tall Ragweed, Texan Great Ragweed, and Wild Hemp. Some of these other common names fit both species.
DESCRIPTION OF THE RAGWEED
Height: Common Ragweed is about 1-6 feet tall. Giant Ragweed is about 2-18 feet tall.
Stem: Its stems are branching. The Common Ragweed stems are green to pink, slightly grooved, and hairy. The Giant Ragweed stems are stiff, rough, and hairy. These stems may exude a red sap.
Leaves: Common Ragweed leaves are alternate near the top and opposite near the bottom. They are bi- or tri-pinnately compound or are finely dissected into narrow segments that are irregularly lobed or toothed. They are about 6 inches long and about 4 inches wide.
Giant Ragweed leaves are opposite. They have stiff hairs, slightly toothed margins, and are deeply palmate with 3-5 pointed lobes. They may also be oval or rounded. They are about 6-12 inches long and about 6 inches wide.
Flowers: The flowers are small and are not showy. They only have disk flowers with no petals. Both sexes are in separate flower heads but are on the same plant.
The staminate (male) flowers are arranged in a long, slender, erect, and central interrupted racemous spike located at the top of the plant. Each flower is stalked, yellow-green, and is arranged upside down. These spikes are about 1-6 inches long in Common Ragweeds and are about 1-10 inches long in Giant Ragweeds,
The pistillate (female) flowers are located in leaf axils. They are sessile, green, and are either solitary or are in small clusters. There are fewer female flowers than male flowers. These flowers mature before the male flowers to insure pollination.
These flowers are wind-pollinated. However, Honeybees (Apis mellifera L.) may gather some of the pollen. Flowering season is July to November.
Fruit: Its fruit is a hard, bur-like, 2-seeded achene. It is top-shaped and is tipped with a stout projection that is encircled by 4-10 short points.
Seeds: Depending upon the size of the plant, Common Ragweed plants may produce about 3000-50,000 seeds. Giant Ragweed plants only produce up to 300 seeds.
These seeds can stay viable for over 5 years and can germinate upon disturbed or nutrient-poor soils. These seeds are eaten by Birds (Class Aves) and by small Mammals (Class Mammalia). The Giant Ragweed seeds may be too large and too tough for some of the smaller birds.
Roots: Its root system is fibrous. Its taproot is shallow.
Habitat: Its habitats consist of abandoned fields, cultivated fields, roadsides, railroads, ditches, and disturbed areas. They are found in open, exposed areas. They may be found in alluvial soils. Common Ragweed prefers dry, low acidic sites and Giant Ragweed prefers moist sites.
Ragweed may be allelopathic to neighboring plants. It may grow tall their 1st year but the poison in the decomposing plant may stunt their growth their 2nd year.
Range: The ranges of both species cover most of North America, except northern Canada. Its range has expanded after the arrival of the European settlers.
Uses of the Ragweed:
Ragweed has some medicinal uses. Both the Native Americans and the early European settlers used this plant. Ragweed was used as an antiseptic, an astringent, an emetic, an emollient, and a febrifuge. The leaves were used as a poultice for insect bites, blood poisoning, poison ivy, minor skin eruptions, infected toes and hives. A tea was made for treating fevers, nausea, intestinal disturbances, nosebleeds, pneumonia, and mucous discharge. The tea was also used as a gargle for mouth sores. The roots were chewed at night to ward off fears.
The pollen of both species was collected as a pharmaceutical for treating ragweed allergies. It is used in modern medicine for allergen immunotherapy.
Ragweed is often consumed by White-tailed Deer (Odocoileus virginianus Zimmermann) or by livestock but may not be a preferred food. This plant has a bitter taste. Dairy cows that eat this plant may produce bitter milk.
Native Americans cultivated the Giant Ragweed seeds as food. These cultivated seeds were lighter in color and were about 4-5 times larger than the wild seeds. They contained about 47% crude proteins, about 38% crude fats, and about 20% edible semi-drying oils. Remains of these seeds have been uncovered at some archaeological sites.
Seeds of both species can sometimes get mixed in with harvested grains. Ragweed seeds will give bread a bitter taste.
Ragweed is good as a soil preserver. If an area is disturbed by fire, flood, or any man-made activity, Ragweed is a pioneer species and is often the first plant to colonize the area and prevent soil erosion. Newly-exposed soil may have about 100,000 dormant seeds per square meter.
Ragweed is also a good soil conditioner for the farmers. It contains nitrogen and other nutrients. Before they flower, farmers may cut or plow this plant under and use it as a “green manure”.
Ragweed is useful in phytoremediation. It is useful in removing heavy metals, such as lead, from the soil.
Ragweed pollen, an allergen, is the main culprit of hay fever. It is most active during August and September. Over 90% of peoples’ allergies are from Ragweed pollen.
The pollen grains are yellow, tiny, rugged, spiny, and numerous. One hundred grains, laid side-to-side, may cross the head of a pin. A single plant may produce up to 1 billion pollen grains.
These grains are windborne. They can remain airborne for several days and can travel great distances and heights. They have been found 400 miles out at sea and at heights of 2 miles. However, their highest concentration is within a hundred yards of the plant.
Future of Ragweed:
Global warming is presently contributing to hay fever. As the amount of carbon dioxide increases in our atmosphere, Ragweed plants become larger and produce more pollen and seeds. Future generations may suffer more than our present generations.
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