According to genetic results in the Ward et al 2022 phylogeny, Amphibolips cookii is likely the alternate generation of the same species that induces Amphibolips quercusinanis. In the table where this speculation is listed, A cookii is labelled as a sexual generation and A quercusinanis as an agamic gall, but this is contradicted by prior literature and may be a mistake.
Amphibolips quercusinanis is a common and distinctive gall found throughout the range of Quercus rubra. It is most commonly confused with Amphibolips confluenta/quercusspongifica, which is larger, more frequently aborts its host leaf, and tends to lack spots and have a bumpier, thicker shell. However, these characters can be misleading, and the most decisive way to tell the species apart is by comparing the internal structure. Amphibolips quercusinanis has an empty interior full of smooth, radiating strings, where confluenta has an interior either densely packed with spongy material or at least with spongy fibers. The presence of spots is especially misleading toward the southern edge of its range, where confluenta is apparently more likely to have spots and quercusinanis is less likely to occur at all.
It can also be confused with Amphibolips quercusostensackeni, especially early in the spring, which has a similarly thin shell and empty interior with smooth fibers, but which lacks spots, remains much smaller throughout the season, and does not distort the host leaf.
In the fall, Amphibolips cookii is often mistaken for quercusinanis. Both galls have spots and lack a spongy interior, but can be distinguished by their placement (cookii is found on buds, not leaves), their appearance (cookii has thicker, more succulent walls and fibers), and most easily by their season of appearance (cookii in the fall, quercusinanis in the spring).
In some parts of its range, Amphibolips quercusinanis co-occurs with Atrusca quercuscentricola, an oak apple of similar size, pattern, and structure found on Quercus stellata. Aside from its host, which is often not apparent if the gall is found on the ground, Atrusca quercuscentricola has a more yellow-orange appearance and red spots, light pubescence, and occurs in the fall. It is common in Arkansas and Missouri, where Amphibolips quercusinanis is found but relatively rare.
The gall of this species has at least once been found on the flower stalk rather than the leaf.
