Nymphoides peltata (S.G.Gmel.) Kuntze, commonly known as yellow floating heart, is a perennial hydrophyte of the Menyanthaceae family. It grows in still or slow-flowing rivers and its indigenous range is extensive, including most of Europe, Asia Minor, north-central Russia (Tutin 1972) and Japan (Zoku 1965). The Nymphoides genus has approximately 50 species (Tippery & Les 2011), 13 of which are considered indigenous to Africa and Madagascar (Raynal 1974).

Within Africa, N. peltata has been recorded outside of cultivation in Ghana (JIRCAS 2010) and Algeria (De Bélair 2010). De Bélair (2010) listed N. peltata as indigenous to Algeria based on a record of one population near the town of Ben Azzouz. The absence of any record of this species in earlier botanical literature covering this region (Gubb 1909; Quezel & Santa 1962; Raynal 1974; Wild 1961) suggests that it may be an introduced species that has escaped from cultivation.

Five Nymphoides species are indigenous to southern Africa and to date no naturalised non-indigenous species have been recorded (Bredenkamp 2006; Cook 2004; GBIF 2017; SAPIA 2016; Whitehouse 1996). Despite this, N. peltata is listed on the South African National Environmental Management: Biodiversity Act (NEMBA) regulations (NEMBA 2014) as a Category 1a species, making it a species requiring compulsory control and eradication. This pre-emptive measure was based on N. peltata being invasive in Canada (Darbyshire & Francis 2008) and Sweden (Larson & Willén 2006), as well as naturalised in the American states of Tennessee (Chester 1996), Oklahoma, New York and Arizona (Clarke 1937; Correll & Correll 1972; Crow & Hellquist 2000).

Nymphoides peltata is cultivated as an ornamental plant in garden pools (Chester 1996) and aquaria (Allgayer & Teton 1987). In 2007, a landowner from Gauteng, South Africa, reported a cultivated population growing so prolifically that he needed assistance in its control (Henderson 2017). It was growing in an artificial, contained pond and was probably destroyed, as recent attempts to find this population have been unsuccessful (D. Cindi [South African National Biodiversity Institute], pers. comm., 01 November 2016).

This article reports the first record of N. peltata outside of cultivation in South Africa.

An unknown Nymphoides species was reported in two dams adjacent to the Mgeni River in the KwaZulu-Natal Midlands (S29.44952° E30.31430°; Figure 1) in January 2016 (H. Grobler [Karkloof Safari Spa], pers. comm., 28 January 2016). Herbarium voucher specimens were collected and submitted to the KwaZulu-Natal Herbarium and were identified as N. peltata by the author. This was done through comparing the voucher specimens to the existing collections of this genus and to descriptions in the relevant literature (Darbyshire & Francis 2008; Mackinder 1990; Tippery, Les & Jones 2012; Whitehouse 1996). The Compton (NBG), KwaZulu-Natal (NH), Bews (NU) and the National Herbarium (PRE) did not have any specimens of N. peltata.

Nymphoides peltata was discovered in two dams that are part of a series of interconnected dams that are also connected to the Mgeni River, upstream of where the Mgeni joins the Karkloof River. The two dams have areas of 3.2 and 0.2 ha, and have N. peltata concentrated along the dam edges amongst indigenous sedges (Figure 2). In 2016, the N. peltata flowered from January to April, dying back in the winter months, and in 2017, it flowered again in January. Hippos (Hippopotamus amphibius L.) on a game farm on which the dams are located were seen eating N. peltata (P. le Roux [Karkloof Safari Spa], pers. comm., 09 February 2017).

The origin of this N. peltata population is currently unknown. The seeds are dispersed through water and by birds, being disc shaped with marginal trichomes that can stick to waterfowl (Cook 1990). This is a possible pathway through which the plant could have arrived at these dams.

In its native range, N. peltata shows pioneer plant characteristics and can colonise large areas through vegetative growth in a season (Brock et al. 1983). Nymphoides peltata has had a significant impact on habitat structure and competitive interactions in the Swedish lakes where it has become established (Josefsson & Andersson 2001) and a weed risk assessment by the United States Department of Agriculture ranked the species high for impact and spread potential in the United States (USDA 2012).

Considering its impact elsewhere, this species warrants further research and a detailed weed risk assessment as laid out by Kumschick et al. (2015). A management plan has already been submitted to the Department of Environmental Affairs (Cindi 2016). However, surveys of nurseries and water bodies would help to get a more accurate delineation of N. peltata’s distribution and possible origin.