Amphibolips quercusspongifica

Family: Cynipidae | Genus: Amphibolips
Detachable: integral
Color: brown, green
Texture: bumpy, hairy, hairless
Abdundance: abundant
Shape: sphere
Alignment: integral
Walls: thin, spongy
Location: petiole, leaf midrib, on leaf veins
Cells: monothalamous
Possible Range:i
Common Name(s):
Amphibolips caroliniensis
Amphibolips coccinea
Amphibolips cocciniae
Amphibolips confluens form spongifica
Amphibolips longicornis
Amphibolips spongifica
Cynips confluens
Cynips quercus coccinea
Cynips quercus spongifica
Cynips spongifica
Trissandricus maculipennis
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  • image of Amphibolips quercusspongifica

Gallformers ID Notes

This species is the most commonly observed cynipid gall in the eastern US, and readily recognized by its size, placement, and spongy interior. There is substantial taxonomic confusion in the distinction between A confluenta and A quercusspongifica. In his initial description, Osten Sacken noted that his "Cynips confluens" likely had two generations, one emerging in the early summer, the other in the fall. He also noted that the species had multiple morphologies on different hosts. Later work has muddled these two distinctions by placing A quercusspongifica as the fall, sexual generation and A confluenta as the spring, agamic generation, and placing both on a variety of red-group oaks. The two were synonymized by Beutenmuller, but Kinsey considered the research proving they are alternating generations inadequate, and Weld treated them as distinct species pending "further study" but noted they are "probably" synonyms. It is not clear whether these two generations/species can be distinguished by gall morphology, or whether distinctions noted between the two reflect differences in host species (eg the galls are pubescent on oaks with pubescent leaves).

On red-group oaks, A confluenta/quercusspongifica is commonly confused with A quercusinanis, which also occurs on leaves in the spring but which has a uniformly smooth exterior with distinct spots, A quercusostensackenii, which is much smaller and doesn't distort the host leaf, and A cookii, which occurs on buds in the fall and has larger spots and thicker walls. A confluenta typically has a bumpy surface. The most definitive way to distinguish it is to note the spongy interior; A quercusinanis and A quercusostensackenii has a stringy, empty interior, while A cookii has thick, succulent fibers.

Some specimens that otherwise resemble A confluenta, especially in Texas , do have spots. This may represent a different species but is more likely a host- or generation-related variation (these spotted variants are typically but not definitively or exclusively associated with Quercus buckleyi and shumardii, as well as potentially Quercus pagoda in Arkansas).

A confluenta/quercusspongifica early in the spring can also be confused with Dryocosmus quercuspalustris, which also forms green, spherical, integral leaf galls that distort leaves. The galls are easily differentiated by their internal structure, which can be observed by shining a bright light through the gall or but cutting it open. D quercuspalustris has a loose larval cell freely rolling around in an otherwise empty chamber. D quercuspalustris galls are much smaller and differ subtly but distinctly in texture. A confluenta/quercusspongifica galls almost always completely deform their host leaves, to the extent that they are often barely visible, while D quercuspalustris galls may seem to almost completely displace the leaf (especially early in leaf out) or have minimal effect on its overall structure (later in the season).

- Gallformers Contributors: (2021) Gallformers ID Notes©

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