Distribution and sexual reproductive potential of Iris pseudacorus L. (Iridaceae) in South Africa

Abstract

Iris pseudacorus L. (Iridaceae), or yellow flag iris, is an emergent aquatic macrophyte which has been distributed globally as an ornamental pond plant. The species spreads rapidly through both sexual and vegetative means, and can become highly invasive in its introduced range. Iris pseudacorus is a declared invader in South Africa, but little is known about the distribution and invasive potential of the species in the Southern Hemisphere, potentially hindering the effectiveness of control efforts. This study addresses this knowledge gap in a South African context, providing insight into the invasion autecology of I. pseudacorus in the country. Through field surveys, we confirmed the presence of the invader in eight of the country's nine provinces and, as of March 2023, we report a four-fold increase in the number of distribution records obtained since 2015. Additionally, we determined a high sexual reproductive output and germinability which resulted in a mean of ∼ 774 germinable seeds produced per m2 across the invasive South African range. By mapping the confirmed distribution of the species in South Africa and quantifying its sexual reproductive output and germinability of its seeds, these results will better equip control organisations to manage I. pseudacorus invasions in South Africa to mitigate its ecological impacts.