Text and photos: Ali Rubio (Herbario Paul C. Standley, IAD)
The family is well recognized for its unique characteristics and is very easy to recognize because its flower has the general appearance of sunflower variants. The main characteristic of the chapter is to be formed, generally, by numerous small tubular shaped flowers, which may or may not have ligules, and these ligules are the protruding structures resembling petals (Tapia Muñoz, 2010).
Their wide distribution is highly due to their great diversification. This family carries great commercial importance: ornamental, edible and medicinal (Rahman, et al., 2008, Adedeji & Jewoola, 2008). The largest exponent of edible species of importance is Lactuca sativa L., which is commonly known as lettuce. It is also possible to mention the calendula (Calendula officinalis L.) from which oil is extracted and the stevia (Stevia rebaudiana (Bertoni) Bertoni, which is used as a sweetener (Del Vitto & Penetenatti, 2009).
In addition, all characteristics represented in this family, from herbs to trees and even succulents, with its high diversity can be deduced from the mechanisms developed both for reproduction and its great ability to survive in all types of environments, from sea level to alpine areas (Tapia Muñoz, 2010, Del Vitto & Penetenatti, 2009).
This characteristic in particular is what has categorized some members of this family as weeds, since it is very easy for them to prosper in hostile environments (Tapia Muñoz, 2010). It may be difficult to imagine that a species related to the sunflower can be considered a weed when one considers its displays of color and grace.
So, what constitutes a weed? In general, a weed has been defined as: a plant that develops in places where it interferes with the objectives of agricultural work. In other words, the crop not not being cultivated is the weed.
The problem with weeds lies in their interaction with the target crop and their competition for resources and allelopathies, the influence of a chemical compound released by a plant on the development and growth of another plant . In this sense, weeds in general have physiological, reproductive, adaptability and resistance to environments that other plants do not.
However, many of the Asteraceae species considered as weeds are being investigated for their medicinal properties, to mention a few, Tridax procumbens L., Bidens pilosa L., Eclipta prostrata L., Synedrella nodiflora (L.) Gaertn. Likewise, authors such as Pappan & Thomas (2017) list, in addition to those already mentioned, Emilia sonchifolia (L.) DC and Crassocephalum crepidioides (Benth.) S. Moore., In their work “Contribution of invasive plants in herbal medicinal practices” .
As already mentioned, the term weed depends on the context, if one of these species were cultivated to extract its active principle for the elaboration of medecine, the weed in this case would be the bean, the corn, and any other unwanted crops.
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