This, like A. grandis, is an exceedingly variable species. The ranges of the
two are almost coincident, except that the first, A. macrostachya, is not now
known to occur in the lowland Atlantic drainage region of Guiana. Three minor
infraspecific populations within A. macrostachya (as within A. grandis), have evolved, two of them previously recognized, and a third which occurs locally in the upper Orinoco and Rio Guainia drainages, is herein proposed as new.
Sussenguth and Beyerle report a third sepal for specimens (or a specimen) examined by themselves. In the review of 48 sheets, I have not been able to demonstrate the presence of a third sepal, and therefore must conclude that it is of exceedingly rare occurrence, and (as also for A. grandis) cannot be considered as characteristic.
In the examination of numerous unopened flower-buds, there has been detected the prevalence of three filiform staminodia, which are alternate with the stamens and attached at the base of the corolla-tube.