Introduction Most recently, treatments of the pantropical genus Piper L. (Piperaceae) included more than 2000 species (Quijano-Abril et al., 2006). The phylogenetic position of Piper L. and of family Piperaceae was inserted within the complex basal group of dicots termed "paleoherbs" (Loconte and Stevenson, 1991). More recently, APG IV (Angiosperm Phylogeny Group et al., 2016) inserted Piperaceae in order Piperales, nested within Magnoliids. The distribution of Piper is pantropical and the genus develops highly variable growth forms and biomechanical organization (Isnard et al., 2012). The highest number of species can be found in the Americas, where 500 species were listed earlier (Burger, 1972; Tebbs, 1993), which then increased to at least 1100 (Jaramillo et al., 2008) and most recently up to 1804 (Ulloa Ulloa et al., 2017). The exact number of Piper species and their exact distribution is not easy to ascertain, particularly due to the high number of taxa, some of which are difficult to distinguish from one another, resulting in many synonyms (Suwanphakdee et al., 2016). Furthermore, some species are widespread, such as P. umbellatum, while others, actively cultivated, escaped by accident and may have been naturalized, such as P. auritum, P. nigrum, or P. methysticum (Smith et al., 2008). Most species show a restricted distribution area (Marquis, 2004; Quijano-Abril et al., 2006). New species were also recently described from old herbarium collections (Görts-Van Rijn and Callejas Posada, 2005). Only two endemic species are currently known for the African continent: P. guineense and P. capense. Piper guineense is a dioecious vine, relatively similar to the majority of southwestern Asian species, whereas P. capense is a shrub with bisexual flowers, hence resembling many species of the American continents (Smith et al., 2008). The knowledge of the genus in Madagascar is far from complete. Currently, P. heimii C.DC. and P. pachyphyllum Baker are indicated for the island, while P. borbonense (Miq.) C.DC. was described for the island called at that time Île Bourbon, currently La Reunion (Weil et al., 2017), belonging to the Mascarene Islands, 600 km east of Madagascar. Its presence in Madagascar is a matter of debate, even if De Candolle (1923, 1869) had assigned some samples from Madagascar and Mauritius to this species (see Appendix 1 about herbarium samples from the site http://www.caryologia.unifi.it/tjb/Appendix1. pdf). However, this species is cultivated, which makes it more difficult to assess its natural distribution.
