POTAMOGETONACEAE

Mead, A., Carlton, J. T., Griffiths, C. L. & Rius, M., 2011, Introduced and cryptogenic marine and estuarine species of South Africa, Journal of Natural History 45 (39 - 40), pp. 2463-2524 : 2511

Family POTAMOGETONACEAE

Stuckenia pectinata (Linnaeus, 1753) Cryptogenic (= Potamogeton pectinatus ; = P. pectinatus ungulatus Hagstrom, 1916 )

This macrophyte, known as pondweed, is the most widely distributed species of Stuckenia (long known in almost all South African literature as Potamogeton ) in the world ( Kaplan 2008). Despite its well-known weedy proclivities, there appears to have been little global analysis, based either on historical or genetic data that might elucidate its biogeographic tracks ( Mader et al. 1998, were able to examine the genetic variation of northern, but not southern, African stocks of Stuckenia pectinata ). Nevertheless, the ancestral distribution of the genus is rooted, as it were, in the northern hemisphere ( Lindqvist et al. 2006), and Stuckenia pectinata , although widespread in northern waters, is highly patchy and isolated in the southern hemisphere ( Santamaria 2002), which is strongly suggestive of recent colonization potentially mediated by human-related vectors. While long-distance bird (in particular swan) dispersal appears to have played a role across Eurasia ( Mader et al. 1998), human-mediated mechanisms may be more at play in interhemisphere dispersal.

The extensive South African biological and ecological literature is summarized in part in Byren and Davies (1986), Thornton et al. (1995), Adams et al. (1999), and Riddin and Adams (2008). Although Stuckenia has been said to have so-called “positive” impacts in South African estuaries related to refugial habitat for juvenile fishes ( Thornton et al. 1995), it can become sufficiently dense to be a nuisance to recreational users, and biological control has been attempted in South Africa ( Schoonbee 1991). If Stuckenia proves to be introduced (by genetic analysis that might suggest, for example, both European linkages and reduced haplotype diversity), it would be of no small interest to experimentally determine how the extensive beds of this pondweed (such as those in the Zandvlei) have acted to displace or replace native aquatic flora or infauna, impacted sediment dynamics or nutrient turnover. Relative to the latter, Stuckenia pectinata appears to be important in estuarine phosphorus cycles ( Thornton et al. 1995; Adams et al. 1999). The earliest record we have found to date is that of Hagstrom (1916), who described Potamogeton pectinatus var. ungulatus (now regarded as a synonym of Stuckenia pectinata ; Kaplan 2008), from the Koude River, Cape Province (www.aluka.org, accessed August 2009; specimens collected in 1896 by F. R. R. Schlecter and deposited in the South African National Herbarium in Pretoria). However, we have no doubt that earlier records will surface.