First records of American Wolffia columbiana in Europe – Clandestine replacement of native Wolffia arrhiza?

Abstract

Wolffia columbiana is a member of the family Lemnaceae and native to the Americas. In 2013, the first two occurrences of Wolffia columbiana in Europe were found in Germany and the Netherlands. Differentiation between W. columbiana and the rare native W. arrhiza is difficult and a scanning electron microscope (SEM) was used to confirm plant identification. A brief description of both populations of W. columbiana and some identifying characteristics are given. Due to their small size, Wolffia species are easily overlooked in the field and/or misidentified, and thus it seems likely, that even more unknown occurrences of alien Wolffia species might occur in Europe. The remaining known occurrences of putative W. arrhiza should be inspected to check their identity. We hypothesize, that alien W. columbiana might be sometimes overlooked or misidentified as the native W. arrhiza, and thus it may have a more widespread distribution within Europe than thought.

Wolffia columbiana and W. globosa (Araceae) new to Britain

“…Counts of stomata using a dissecting microscope suggest that populations of W. columbiana recorded in north-western France had <10 stomata per frond, whereas counts from material from the Gwent, Pevensey and Somerset Levels typically had (8-)10-20(-25). Schmitz et al (2014) using SEM noted that counts from German populations found 3-14 stomata per frond (mean 5.5) and Dutch populations 3-11 per frond (mean 6.4). Landolt (1986) notes that "In Florida, there are clones of W. columbiana which have up to 30 stomata and therefore resemble W. arrhiza".…”

“…They are composed of a photosynthetic upper part which is green and opaque, below which there is an expanded lower layer which is firm and may be green or colourless. Landolt, 1986;Landolt, 1994;Landolt, 2000;Bog et al, 2020) Character W. arrhiza W. australiana W. columbiana W. globosa Species of Wolffia can be very difficult to identify, particularly as counting stomata appears to be unreliable without recourse to Scanning Electron Microscopy (SEM) (Schmitz et al, 2014;W. van der Wen pers.…”

“…comm.). In spite of this, many species have been recorded outside their native range (Table 3), with species originating in the Americas (W. columbiana), Asia (W. globosa) and Australasia (W. australiana) (Armstrong & Thorne 1984, Landolt 1986, Mazzeo et al 1993, Landolt 1994 all occurring in Europe (Kirjakov & Velichkova 2013, Schmitz et al 2014, FLORON 2021. An attempt has therefore been made here to provide guidance on all known species worldwide, while details are provided (Table 2) for the species known to occur in Europe.…”

“…Since 2013, three non-native species have been recorded in Europe: W. columbiana H. Karst. (Schmitz et al 2014), W. globosa (Roxb.) Hartog & Plas (Kirjakov & Velichkova 2013) and W. australiana (Benth.)…”

Wolffia globosa (Araceae s. l. / Lemnaceae s. str.), a new aquatic alien species in the flora of Ukraine

“…Hartog & Plas (Au), W. globosa (Roxb.) Hartog & Plas (As) (Sell, Murrell, 1996;Mesterhá et al, 2007;Banaszek, Musial, 2009;Misud, 2010;Iberite et al, 2011;Schmitz et al, 2014;Kirjakov, Velichkova, 2016;Feráková, Onderíková, 1998;Hendrickx, Verloove, 2019;Lecron et al, 2021;Niebler et al, 2021;Lansdown et al, 2022); на Близькому Сході були виявлені Landoltia punctata (G. Mey.)…”