Leucas martinicensis (Jacquin, 1760) Brown, 1810

González-Gallegos, Jesús Guadalupe & Vibrans, Heike, 2022, Leucas martinicensis (Lamiaceae, Lamioideae), a new naturalized species in Mexico, Phytotaxa 552 (2), pp. 166-170 : 166-168

Leucas martinicensis

can be distinguished by its annual habit, ovate to ovate-lanceolate leaves, retrorsely pubescent stem, several axillary whorls along each branch, oblique calyces that are constricted near the throat, with an apical portion reflexed in fruit, calyx teeth as long as the tube, and delicate white corollas barely longer than the calyx and sometimes tinged with red ( Brown et al. 1912, Li & Hedge 1994, Morales 2011).

Though most recorded specimens are from Africa , there are scattered occurrences throughout tropical Asia and Australia. In the Americas , it is known mainly from Brazil, and several Caribbean islands (GBIF Secretariat 2021, POWO 2021, REFLORA 2022). Interestingly , there is some controversy on the origin of this plant. Scheen & Albert (2009) indicate an African origin, but Morales (2011) states that it probably comes from America. However, an African or at least an Old World origin is much more plausible considering the center of species richness of the genus, the distribution of close relatives and related genera. The species probably arrived in the Caribbean relatively early during the European colonization as the epithet refers to the island of Martinique in the Lesser Antilles, and the type specimen may have been collected there. The distribution of the species in America has remained restricted to the Caribbean and South America (GBIF Secretariat 2021).

We do not know how the species arrived in Mexico. It is not particularly attractive, but it is intensely aromatic and used as a medicinal tea in Africa, China, India, and Brazil ( Li & Hedge 1994, Chouhan & Singh 2011, Gomes de Melo et al. 2011, Ugwah-Oguejiofor et al. 2015); as habitually observed in many plants of Lamiaceae family (e.g., Heinrich 1992, Lawrence 1992, Rivera-Nuñez & Obón de Castro 1992, Perrino et al. 2021); also, it is burned as an insect repellent ( Li & Hedge 1994). Its main aromatic component is Germacrene-D, a known insecticide ( Muhayimana et al. 1998, Ravi-Kiran & SitaDevi 2007, Rattray & Van Wyk 2021). Antioxidant properties have been reported ( Rattray & Van Wyk, 2021). Also, Leucas martinicensis is used as an anticonvulsive and sedative ( Ugwah-Oguejiofor et al. 2015). These characteristics may facilitate intentional dispersal by humans, but the almost simultaneous appearance in widely separate places suggest unintentional introduction with commercial products.

In Africa, Leucas martinicensis is a widespread ruderal and segetal weed ( Weber et al. 1995, Sheen & Albert 2009, Azanaw et al. 2020); elsewhere, it is reported from ruderal and/or disturbed vegetation. The conditions of the habitat of the three populations in Mexico are consistent with these reports from the literature as described above. It will probably not invade more natural habitats but may cause problems for agricultural activities in the future, and specific eradication measures should be verified. The documentation of this new resident of the Mexican flora will facilitate tracking its future behavior.

Specimens examined:— MEXICO. Sinaloa. Badiraguato: La Pitahayita, 1 km al SW, 25º40.687’N, 107º22.608’W, 1094 m elev., 12 October 2021, J.G. González-Gallegos, F. Pío-León, J. Noriega & A. Zúñiga-Martínez 2635 (CIIDIR!, IBUG!, MEXU!, UAS!)