Side by side, these two species are easier to distinguish than when apart. Spirodela polyrrhiza is the largest duckweed and has more roots than others in North America. Landoltia punctata usually has several roots, generally fewer than S. polyrrhiza, but, always more than Lemna species, which only have one. Both Spirodela and Landoltia have reddish purple coloration on the undersurface of the fronds, a result of anthocyanin production, which varies with environmental conditions. The undersurface of Landoltia punctata is covered with many sunken glands, reason for the epithet "punctata", that are seen as a heavier texture overall.