Ludwigia mullertii is a trade name of the hybrid ludwigia Ludwigia palustris × repens.1 Wild hybrids are recorded from Chiapas (Mexico), but the aquarium plant probably arose in cultivation.15 The trade name appeared as early as 1892 in the journal “Aquarium” (Brooklyn); POWO does not assign it to any species.2 The hybrid was not formally described until 2000, as Ludwigia × kentiana.13 Naturalised occurrences are also known, for example from Germany and England.1
Under water it cannot be reliably distinguished from its parent species.1 Flowering emersed plants differ: L. palustris has no petals, L. repens four yellow ones and the hybrid up to four small petals that soon drop and are described as cream-coloured or yellow.145 It grows fast, tolerates very different water conditions and turns a strong reddish colour only under bright light; as a group it suits the midground and background.15
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