The Salicaceae Mirb. family, to which the Xylosma genus belongs, is famously medicinal because of the Salix genus (willow), the pharmacological properties of which were already used in ancient Mesopotamia, and were extolled in the first century CE, in Dioscorides’ De Materia Medica ^[1][2][8,9].

The Xylosma genus is one of the 55 that conform the Salicaceae family ^[2][9], and is composed of 100 accepted species ^[3][10], although others list 45 ^[4][11]. Until recently, it was included in the now-deprecated Flacourtiaceae family, but has now been assigned to Salicaceae ^[5][12]. The name stems from the Greek words for “wood” and “smell” in reference to odoriferous quality of the wood of some Pacific species of the genus ^[4][11], presumably X. orbiculata and X. suaveolens used to perfume coconut oil by early South Pacific inhabitants ^[6][13]. At first, the genus was named Myroxylon (myrrh-wood) but was changed to Xylosma to avoid confusion with South American balsam trees ^[7][14]. Not all species in the genus are sweet-smelling: X. maidenii timber, for example, is foul-smelling. Xylosma species are described in detail by Woodson et al. ^[8][15].

Species in the Xylosma genus have several uses and properties, from landscaping (Xylosma congesta (Lour.) Merr.), beekeeping (Xylosma venosa N. E. Br. ^[9][16]), timber, firewood, to food and medicine; notably Xylosma longifolia Clos. Due to the thorns that some species of the genus have, common names such as “do not touch me” (Xylosma coriacea (Poit.) Eichler) or “deer antlers” (Xylosma spiculifera (Tul.) Triana and Planch.) are used for them ^[10][17]. Eleven species of the genus, particularly Xylosma vincentii Guillaumin, are known to be nickel hyperaccumulators ^[11][12][18,19] which presents potential for phytoremediation and phytomining ^[13][20].

Species belonging to the Xylosma genus are present in subtropical America, Southeast Asia, and Oceania. Of the 100 species listed in the genus ^[3][10], 61 are found in America, 8 in Asia, and 31 in Oceania. Figure 1 shows examples of species of the genus. The map in Figure 2 shows the intertropical, and to a lesser extent, temperate, distribution of Xylosma species, by country.

Of the 100 species of the genus, 7 are listed as vulnerable, 9 as endangered, and 6 as critically endangered. In total, 22% of the species in the genus are considered as species of concern ^[14][21]. This should be considered when evaluating potential industrial uses for these species.

3. Ethnopharmacological and Ethnoveterinary Usage

Of the 100 species of the genus, few appear in the scientific literature, and even fewer are mentioned from an ethnopharmacological or ethnoveterinary perspective. Notwithstanding, Xylosma species are a part of the traditional Chinese medicinal system, with documented uses of X. congesta appearing as early as the XVI century CE ^[15][25]. Few of the Xylosma species are recognized as medicinal. Table 1 summarizes the species with reported medicinal use along with their stated ethnopharmacological uses, when available. The Anatomical Therapeutic Chemical (ATC) Classification by the World Health Organization (WHO) is used to classify the uses for each species ^[16][26]. Not all species are identified in the literature, with general mentions as “Xylosma sp.” in some cases. According to the ATC classification, the most frequent uses of Xylosma spp. in ethnopharmacology are dermatological, nervous system, and respiratory system, with 17% of the uses each, alimentary tract and metabolism with 11%, and genitourinary system and sex hormones with 6%. Additionally, 11% of the uses are veterinary. As to the morphological structures used, the most common are leaves and barks with 33% each, and both stems and roots with 11% each.

4. Biological Activity

Biological activity tests of Xylosma have been carried out mostly in vitro, with no reported in vivo research, with plant extracts, be they leaf, root, bark, or the whole plant. Different solvents and solvent mixtures have been used for the extracts, mainly methanol and ethanol.

In Vitro Activity

In vitro research on biological activity of Xylosma species centers around 7 identified species and one unspecified one. The research figures are summarized in Figure 45, and the research is detailed in Table 2.