**1. Introduction**

Ten percent of all vascular plants are used as medicinal plants [1], and there are estimated to be between 350,000 [2] and almost half a million [3] species of them. Since ancient times, plants have been used in medicine and are still used today [4]. In the beginning, the trial and error method was used to treat illnesses or even simply to feel better, and in this way, to distinguish useful plants with beneficial effects [5]. The use of these plants has been gradually refined over the generations, and this has become known in many contexts as traditional medicine. The official definition of traditional medicine can be considered as "the sum total of the knowledge, skills and practices based on the theories, beliefs and experiences indigenous to different cultures, whether explicable or not, used in the maintenance of health, as well as in the prevention, diagnosis, improvement or treatment of physical and mental illnesses" [6].

It is a fact that all civilizations have developed this form of medicine [7] based on the plants in their own habitat [8]. There are even authors who claim that this transmitted knowledge is the origin of medicine and pharmacy. Even today, hundreds of higher plants are cultivated worldwide to obtain useful substances in medicine and pharmacy [9]. The therapeutic properties of plants gave rise to medicinal drugs made from certain plants with these benefits [10].

Until the 18th century, the therapeutic properties of many plants, their effect on the human organism and their method of treatment were known, but the active compound was unknown [11]. As an example, the Canon of Medicine written by the Persian physician and scientist Avicenna (Ibn Sina) was used until the 18th century [12].

The origin of modern science, especially in the Renaissance, in particular chemical analysis, and the associated instrumentation such as the microscope, was what made it possible to isolate the active principles of medical plants [13]. Since then, these active principles have been obtained synthetically in the laboratory to produce the medicines later [14]. The use of medicines was gradually expanded. Until today, the direct use of medicinal plants is apparently displaced in modern medicine [15]. Today's medicine needs the industry producing pharmaceutical medicines, which are largely based on the active principles of plants, and therefore, these are used as raw materials in many cases [16]. Yet, today, the underdeveloped world does not have access to this modern medicine of synthetic origin, and therefore, large areas of the world continue to use traditional medicine based on the direct use of medicinal plants due to their low cost [17].

However, it should be noted that the possible trend to return to this type of traditional medicine may have two major drawbacks. The first is the use of medicinal plants without sanitary control, without thinking about the possible harmful aspects for health [18]. Although many plants do not have side effects like the aromatic plants used in infusions: chamomile, rosemary, mint, or thyme; however, others may have dangerous active principles. To cite an example, Bitter melon (*Momordica charantia L.*) used to cure fever and in cases of malaria [19], its green seeds are very toxic as they can cause a sharp drop in blood sugar and induce a patient's coma (hypoglycemic coma) [20]; this is due to the fact that the components of bitter melon extract appear to have structural similarities to animal insulin [21]. Secondly, there has been a proliferation of products giving rise to false perspectives, as they are not sufficiently researched [22].

Examining the specialized literature of reviews and bibliometric studies on medicinal plants, three types of studies are found: those focused on a geographical area, those focused on a specific plant or family, and those focused on some type of medical interest activity. Regarding the studies of geographical areas, for example, there are the studies of Africa. Specifically, in South Africa, the plants that are marketed [23], as these plants of medical interest have been promoted [24], or for the treatment of specific diseases such as Alzheimer's [25]. In Central Africa, the studies of Cameroon are remarkable, where for general bibliometric studies of its scientific output, the topic of medicinal plants stands out as one of the most important in this country [26]. Or those of Ghana, regarding frequent diseases in this country such as malaria, HIV/AIDS, hypertension, tuberculosis, or bleeding disorders [27]. Other countries that have conducted a bibliometric study of their medicinal plants have been Cuba [28] and China [29].

The other direction of the bibliometric studies mentioned, those that focus on specific plants, are those of: *Artemisia annua L.* [30], *Aloe vera* [31], *Panax ginseng* [32], *Punica grantum* L. [33], *Apocynum cannabinum* [34], or *Andrographis paniculata* [35]. The third line of the bibliometric research on medicinal plants deals with some kind of specific activity; there are studies for example for the activities of: antibacterial or antifungal [36], antioxidant [37], and anticancer [38–40].

As a common feature of the bibliometric studies published so far, none of them has a worldwide perspective. Furthermore, they are generally based on Web of Science and some of them on other more specific databases such as CAB Abstracts or PlantMedCUBA, but no work based on Scopus has been observed. Therefore, this paper aims to study what types of scientific advances are being developed around medicinal plants, what research trends are being carried out, and by which countries and research institutions. To this purpose, it is proposed to carry out a bibliometric analysis of all the scientific publications on this topic.
