It is interesting to note that the common ragweed got its scientific name ambrosia artemisiifolia L. from the prehistoric Greek terminology for the aromatic sustenance of their gods - ambrosia. However, this could somewhat be paradoxical as the class is most familiar for one reality - the pollens of the flowers of this genus gives rise to acute and extensive allergic reactions. Nevertheless, the common name of this genus is in fact similar to the name of the heavenly delicacy, both of which have been drawn from the term ambrotos, meaning 'immortal' in Greek. In the instance of the plants, this term appropriately denotes the obstinateness since it is really difficult to eradicate these plants from an area that they overrun as weeds.
As the name of the genus hints, the common ragweed is among the most widespread weeds that invades nearly all the places. The common ragweed is considered to be a nuisance in fields and grazing lands as although the cattle do not like the plant's astringent juices, many a times, they consume the plant owing to scarcity of better rummage. As a result of consuming this bitter plant, cattle not only produce bitter milk, but also exude a foul smell. Even after take away a grain crop, this weed almost every time crops up in the bristles! Another shortcoming of this plant is that when its flowers contain copious pollens that are believed to be a major reason for hay fever (a seasonal rhinitis resulting from an allergic reaction to pollen). Hence, the plant is not only avoided, but also held in horror by people as they may fall prey to the illness.
The roots of the common ragweed are somewhat deep and branching giving rise to the stems that grow up to five feet. The stems are straight, delicately hairy and branches generously. The leaves of the plant grows alternately are thin and their length varies from two to four inches. The leaves have a profound green hue on the surface, while the underside is pale. These leaves are doubly pinnately cleft providing the plant an open and feathery look. The common ragweed bears two types of flowers whose staminate head stands out in crowded racemes that are akin to spikes at the apex of the plant as well as in its top axils. The involucres or (a collection of bracts subtending a flower cluster) are top-shaped containing five to twelve joint bracts and six to twenty minute green hued flowers. The flowers of common ragweed are approximately one-eighth inch long each and the male flowers generate delicate yellow pollens that are transported by wind effortlessly. Normally, the pollens of the flowers are discharged either in the latter part of summer or early fall. Beneath, the axils, a collection of bracts cover up fertile involucres. Each of these involucres encloses a solitary flower that possesses a unique stretched out branch sticking out from the closed and pointed coronet. When these involucres are mature they take the appearance of hard fruits like achenes (small, dry, hard, one-seeded, indehiscent fruit). The fruits of common ragweed are each about one-eighth inch long, having an oval shape with a curved crown that is encircled by around four to six thorny tips.
As long as these fruits remain on the soil, they have the aptitude to grow into new plants when ever the conditions are suitable. Usually, diminutive fruits of the common ragweed are considered to be a common adulteration of grain and grass and are sometimes handed out in bundled hay. The plant produces innumerable seeds that are viable for germination for a minimum of five years. It may be mentioned here that the common ragweed is monoecious in nature producing separate male and female flowers on the same plant. The common ragweed has a widespread root system that is fibrous in nature.
Most of the species of the common ragweed are indigenous to North America. In fact, the common ragweed is rough and grows annually having coarse bristly stems more often than not having lobes or separated leaves. The common ragweed (scientific name A. artemisiifolia), is called by many names, such as the Roman wormwood, hogweed, bitterweed and hogbrake and is found all over the North American continent. On the other hand, the great or giant ragweed (scientific name A. trifida) is known as bitterweed and/ or horse cane and is indigenous to the region stretching from Quebec to British Columbia and down the south to places like Florida, Arkansas and California. The giant ragweed normally grows to a height of anything between three feet to 17 feet (0.9 meter to 5.0 meter) and possesses three to five lobes leaves.
The common as well as the giant ragweed grow annually and frequently turn out to be harmful weeds. The pollens of this plant that drops in great amount during the latter part of the summer, is considered to be the main reason for hay fever in the eastern as well as middle parts of the North American continent. As the different species of common ragweed grow annually, they can be easily exterminated without effort provided the plants are mowed nicely prior to their shedding the abundant pollens.
Normally, the different species of ragweeds are found in the temperate climatic regions in the Northern Hemisphere and the South American continent. These plants thrive best in grassy meadows receiving abundance of sunlight and having sandy soils, along the banks of the rivers, the roadsides as well as abandoned or vacated lands where the soil is not very fertile.
In all, 41 species of ragweeds are found across the world. Many of these species have even adjusted themselves to the dry climates of the deserts. For instance, Burrobush (A. dumosa) is among the ragweed species that has best adapted itself to the arid conditions in the North American continent. This is a perennial species. Another 10 species of ragweed can be found in the arid conditions of the Sonoran Desert.
It is important not to mix up this genus of plant with another plant also known by the common name 'ragweed' - Kochia scoparia.
The common ragweed or Ambrosia artemisiifolia has a preference for conditions ranging from total sunlight to a little arid condition. In fact, this genus is somewhat unconcerned regarding the soil conditions and has the ability to thrive in soil having extreme amounts of gravel, sand or clay. Precisely speaking, the common ragweed has a penchant for barren soil as this enables the plant to grow without any competition from other plants. The plant's ability to withstand arid or drought conditions is excellent, but when the plant grows in such conditions, it sheds some of its lower leaves in order to retain moisture. As discussed earlier, the plant is often found to be unrelenting and belligerent and quite difficult to get rid of the plot where it is growing. This is primarily owing to the fact that the seeds of common ragweed have the aptitude to remain viable for germination for many years - more than five years. Irrespective of the fact whether it is desirable or not, the common ragweed will normally establish itself in a native environment or a wild flower garden.
Although the seeds of this plant have a somewhat bitter taste, they are an important food for many species of birds during the winter months when other food becomes scarce. Even the larvae of some members of Lepidoptera - butterflies and moths - depend on the plant's seeds for sustenance.
It is interesting to note that a single common ragweed plant is considered to produce as many as a billion pollen grains during a single season. The plant is anemophilous by nature, meaning its pollens are transported by wind. However, the pollens of common ragweed are extremely allergic and believed to be among the worst allergens of all pollens. Worse still, the pollens of this species are the main cause for hay fever in North America and hence are dreaded by the people. In addition, the common ragweed (A. artemisiifolia) along with the Western ragweed (A. psilostachya) is believed to be the most "poisonous" for people who are susceptible to hay fever. In the northern hemisphere, the ragweeds produce flowers between the period from early July and middle of August. Often the plants continue blooming till the arrival of the cooler weather conditions.
Usually, the common ragweed plants produce larger number of pollen grains during the wet years. However, when the humidity goes over 70 per cent, the pollen grains form clusters and are unable to be transported by wind owing to the increase in their combined weight. What is alarming is that the ragweed plant has been identified as a major concern for global warming. This is owing to the fact that several examinations have demonstrated that when the level of carbon dioxide goes up in the atmosphere, it influences the pollen production by the plants. In fact, the greater the levels of carbon dioxide in the atmosphere, the greater is the pollen production by ragweed plants. Normally, when the day is relatively dry and there is enough of wind, the ragweed pollen grains are able to travel several kilometers.
Although many hold the goldenrod to be responsible for hay fever, the fact remains that this is merely an ornamental flower that happens to bloom around the same time as the common ragweed. Contrary to the common ragweed (A. artemisiifolia) which is anemophilous (wind pollinated) by nature, the goldenrod is entomophilous, meaning it is pollinated by insects. As the pollens of goldenrod are sticky and heavy, they cannot be transported by wind.
While the pollens of the common ragweed are harmful for humans, the plant is useful for several types of wildlife. While the ragweed flowers do not attract the normal flower-visiting insects, most honeybees have been seen to collect pollens from the male ragweed flowers. Caterpillars of different types of moths, such as Eynchlora arida (Wavy-Lined Emerald), Tarachidia candefacta (Olive-Shaded Bird-Dropping Moth), Schinia rivulosa (Ragweed Flower Moth), Tarachidia erastriodies (Small Bird-Dropping Moth) and many more, consume the foliage, flowers and/ or the seeds of the ragweed plants. In fact, it has often been observed that certain grasshopper species also found in abundance near the common ragweed growths. This may be owing to the reason that these grasshopper species consume the foliage of the ragweed plants and like the surroundings where these plants grow.
The ragweed seeds enclose rich amounts of oil and this draws several game birds found in the higher altitudes as well as songbirds towards the plants. As the tiny barbs of the ragweed seeds stick out of the snow covered ground during the winter, many birds find it easy to locate the seeds, which they consume during the cold months when other food is scarce. The Thirteen-Lined Ground Squirrel, Prairie Vole and Meadow Vole too eat the seeds of the ragweed plants in some measure. However, it appears that the seeds of the ragweed plants are partly digestible and they are often scattered far and wide by the animals and birds that eat them and later discharge the semi-digested seeds along with their excreta or droppings. The herbivorous mammals do not prefer to consume the foliage of the common ragweed as they are quite bitter to taste.