The smallest species of angiosperms in the world are undoubtedly the small floating aquatic plants of the subfamily Lemnoideae, with 5 genera, all occurring in the New World and Brazil: Landoltia Les & D.J.Crawford, Lemna L., Spirodela Schleid., Wolffia Horkel ex Schleid and Wolffiella Helgelm. Of these, Wolffia members are the smallest there are, with 11 spp. However, there is no exact statistic of who is the smallest, as different sources put certain species as being the smallest. In this text, it is proposed a smaller species in the genus, consequently the smallest species of angiosperm in the world.
To determine the smallest of all Wolffia species, we consulted the most recent review of Lemonoidae species in Klaus et al. (Nordic Journal of Botany, 2020). For each of the 11 spp. proposals, we set up a table with maximum and minimum lengths (a max and min), as well as width (b max and min) of the fronds of each species; still in the table, we calculate the quantities a and b on average.
In sequence, we build a scatter diagram over average a and b, with the same scale. We will consider the smallest species to be the one whose point on the diagram is the smallest distance from the origin of the scales, using Euclidean distance, represented here with concentric circles then centered on the origin.
In the graph it is possible to consider that the smallest species are W. angusta Landolt and W. globosa (Roxb.) Hartog & Plas, with almost equal distance. The absolute data of a and b do not unambiguously allow to determine the smallest, so let's use the formula:
Applying the two species, we have:
Based on this result, we can consider that the smallest vascular plant species elsewhere is W. angusta, native to the Malay Peninsula, New Guinea and Australia (POWO). The seven smallest species are all native to the Old World, and the remaining 4 are all New World. The smallest New World species is W. borealis (Englem.) Landolt. from North America, followed by W. brasiliensis Wedd. - these the smallest angiosperm species in Neotropics, South America and Brazil.