The viability of propagules of alien plant species sold for traditional medicine in South Africa

Invasive alien species are routinely moved around the world as horticultural specimens. An additional route through the traditional medicine trade may exist, especially where cultures from different continents coalesce. South African traditional medicine, for example, has a long history of association with its Indian Ayurvedic equivalent via migration of people from the sub-continent as either slaves or indentured labour. This study investigated the occurrence and viability of alien species in South African traditional medicine markets and shops. Forty-two species of alien plants were found, of which 26 species were propagules and 22 were viable. Seven of the viable species are listed as invasive in South Africa. However, all but one of the 22 species that were tested and identified are known to be invasive somewhere in the world. Most of the viable alien species were sold as seeds, seedpods or nuts (64%, n = 14 of 22 species) from Indian-owned shops, while mainly tubers, stems and rhizomes were found in African-run markets. Alien plant species moving within this trade route have circumvented all dispersal barriers and may have exerted propagule pressure over at least a century, and should therefore be considered as candidates for monitoring.