While often confused in the horticultural trade, particularly when sold as "money trees," *Pachira aquatica* (Guiana Chestnut) and *Pachira glabra* (Saba Nut) are two distinct species within the Malvaceae family. Their differences become apparent upon closer botanical examination of their morphology, reproductive structures, and preferred habitats.
A primary distinguishing feature is the trunk. *Pachira aquatica* develops a significantly swollen or bulbous trunk base, especially noticeable in mature specimens. This adaptation is linked to its riparian nature, as it stores water to survive seasonal flooding and droughts. The bark of *P. aquatica* is typically a smooth grey-brown. In contrast, *Pachira glabra* almost entirely lacks this pronounced basal swelling; its trunk remains more uniform and cylindrical. The bark is also smooth but often has a greener hue when young, maturing to a darker grey.
The flowers of these two species provide the most reliable diagnostic characteristics. Both have large, showy flowers with long, creamy-white to pale yellow stamens, but key differences exist. The flower of *Pachira aquatica* has long, reflexed petals that are reddish-brown on the outside and curve backwards. Its staminal tube, the structure that holds the stamens, is red. Most notably, the flower bud of *P. aquatica* is erect. Conversely, the flower of *Pachira glabra* has petals that are a more uniform greenish-yellow or cream color on the outside and are less reflexed. Its staminal tube is white or a very pale cream. A definitive trait is that the flower bud of *P. glabra* is pendulous, hanging down from the branch before it opens.
The fruits also differ substantially. *Pachira aquatica* produces a large, oblong to ellipsoid woody capsule that can be up to 30 cm (12 inches) long. This large fruit is brown and dehisces (splits open) along five seams to reveal its seeds. The seeds of *P. aquatica* are edible and relatively large. The fruit of *Pachira glabra* is smaller, smoother, and more ovoid or elliptical in shape, typically reaching only 10-15 cm (4-6 inches) in length. Its outer surface is olive-green to brown, and it rarely dehisces completely on the tree. The seeds of *P. glabra* are also smaller than those of its relative.
Their common names offer a clue to their ecological preferences. *Pachira aquatica*, the Guiana Chestnut, is truly an aquatic-adapted species. It is native to freshwater swamps and riverbanks in Central and South America and is highly tolerant of seasonal inundation and wet soil conditions. *Pachira glabra*, while still enjoying moisture, is not as tied to wetland environments. It is native to more upland, seasonally dry tropical forests in eastern Brazil, demonstrating a greater tolerance for well-drained, and occasionally drier, soils. This difference in native habitat is the evolutionary driver behind the swollen water-storing trunk of *P. aquatica*.
