Invasive alien species : potential cheap resources of plant substances for medicinal use *

Kozuharova, E., Ionkova, I. & Raimondo, F. M.: Invasive alien species: potential cheap resources of plant substances for medicinal use. — Bocconea 28: 223-236. 2019. — ISSN: 1120-4060 printed, 2280-3882 online. On the basis of the literature examined, the scientific acquisitions concerning the pharmacological properties and medicinal uses of Ambrosia artemisiifolia and Erigeron canadensis – two American vascular plants of Asteraceae family that have become invasive in Europe and others continents – are collected and discussed. The data reveal the potential of the invasive as cheap sources of compounds with valuable pharmacological activities. In addition to the two plants presented as a case study, there are hundreds of plant species at hand as potential assets to explore and make money.


Introduction
Some alien plant species have high tolerance of various habitat conditions and elevated propagation ability. This promotes their aggressive invasive behaviour. Often they over compete the local vegetation. Additionally many of them suppress the seed germination and seedling development of local plants. In the newly invaded habitats they might not have suitable herbivores to control their populations (DAISIE 2009). The only effective enemy might be Homo sapiens. Humans are known with their destructive power once an object has become significant for industrial utilization. Due to the fact that these are aggressive invasive species, they can provide abundant and cheap resources of plant bioactive compounds which can be used for medicinal purposes. Additionally, excessive harvesting for medicinal use might contribute to decrease their populations and reduce the destructive impact of these species on natural habitats.
The good practice in the traditional use of plants for remedial purposes is a precondition for successful phyto-therapeutic application. On these basis a modern scientific approach such as phytochemical and pharmacological investigations affirms the therapeutic effect.
Echinacea purpurea (L.) Moench. is an example of a plant with growing modern popularity based on good practices in Native Americans' traditional medicine (Austin 2004, Wilkes 2012.
The aim of this contribution is to review research data and reveal the potential of two invasive plants of Asteraceae family as cheap sources of compounds with valuable pharmacological activities.

Material and metods
On the basis of the literature examined, the scientific acquisitions concerning the pharmacological properties and uses of Ambrosia artemisiifolia L. and Erigeron canadensis L., two American species that have become invasive on different continents, are collected and discussed. Some brief botanical, distributive and ecological indications on these two species are given below.
Ambrosia artemisiifolia is an annual plant native to North America across Canada, the eastern and central United States, the Great Plains, and in Alaska; the Caribbean on Cuba, Hispaniola, and Jamaica; and South America in the southern bioregion (Argentina, Chile, Paraguay, Uruguay), the western bioregion (Bolivia, Peru), and Brazil. This species has been introduced in Europe at the end of 19th century in seed crops at various independent geographical points and at various times since its introduction in natural habitats. Recently, the number of naturalized populations increased considerably fast and it is considered to be the one of the most dangerous invasive alien species of Europe (Chauvel & al. 2006;Kazinczi & al 2008;Essl & al. 2009;DAISIE 2009;Hodgins & al. 2013).
Erigeron canadensis [= Conyza canadensis (L.) Cronquist] is an erect, annual plant. It is native throughout most of North America and Central America and invasive in Europe. It was introduced into Europe in the mid 17th century, likely along with Canadian furs shipped to France (Tilley 2012). This plant is associated with disturbed, open and unshaded habitats, such as cultivated land, abandoned fields, roadsides, ruderal places, and other open habitats. Canadian horseweed can reduce crop yields through direct competition for resources. (Tilley 2012). It also contains allelopathic chemicals which can inhibit germination and reduce seedling growth in several species (Shaukat & al. 2003).
On the two plants chosen as a case study (Ambrosia artemisiifolia and Erigeron canadensis), here we present: 1) traditional ethnobotanical data from their native habitats; 2) modern investigations of pharmacological activity and essential secondary compounds.
This species contains phytotoxins and shows significant inhibitory effects on the seed germination and primary growth of crops (Ritter & Coble 1981;Wang & Zhu 1995;Fig. 1. Drawing of Ambrosia artemisiifolia from Bulgarian population (by E. Kozuharova). Brückner & al. 2003;Vidotto & al. 2013). High levels of naturally occurring variation in the ALS gene sequence have been found in A. artemisiifolia allowing rapid and widespread selection for resistance when ALS-inhibiting herbicides are used (Tranel & al. 2004). The main problem is that its pollen is well known as noxious allergen (Mirone & al. 2004;D'Amato & al. 2007;Léonard & al. 2010).
Pharmacological tests revealed that Ambrosia artemisiifolia possess numerous activities such as cytotoxic, antimalarial, antimicrobial, anti-inflammatory, pronounced hepatoprotective and hypolipemic-lowers the concentration of fats in the blood (Table 2).

Candida, Cryptococcus, Trichophyton, Rhodotorula
Extracts of Erigeron canadensis were reported to have anti-inflammatory and anti-proliferative activity as well as gastric ulcer protective effect. Also anti-inflammatory, de-pigmentation, anti-coagulant, anti-platelet and anti-oxidant effects are reported (Table 4).
Health risks or side effects following the proper administration of designated therapeutic dosages were not recorded (Anonymous 2000).

Discussion and conclusion
Ethnobotanical data from their habitats reveal promising medicinal potential. A growing body of scientific literature points to their therapeutic properties. Valuable chemical constituents of these alien invasive species are sesquiterpene lactones, essential oils etc. They posses different activities such as anticancer activity, as well as antitussive, antifungal, antiinflammatory, antinociceptive, hypoglycaemic, antimitotic, antioxidant, antitrypanosomal, CNS depressant activity, diuretic effects, contact dermatitis, insecticidal and herbicidal activities, hepatoprotective and hypolipemic activities etc.
Due to the fact that these are aggressive invasive species, they can provide abundant and cheap resources reach of plant chemical constituents which can be utilized for therapeutic purposes. Additionally, exploitation of the biomass for medicinal use might contribute to relieving the destructive impact of these species on natural habitats.
The invasive plant species considered in this contribution deserve further investigations as they have valuable pharmacological activities. Harvesting of the plants for their medicinal value may reduce the populations due to decreased seed production and propagation. This way additionally the risk of allergy caused by Ambrosia artemisiifolia pollen will decrease.
There are many studies conducted on the two species here examined and there is good reason to believe that there are prospects of study that can still provide other products that can contribute to give further value to negatively evaluated biological resources, since they are seen as harmful and competitive agents and not as a resource. Therefore, unexplored fields remain to which new research can be directed. In addition to the plants presented as a case study, there are hundreds of species at hand as potential assets to explore and make money.