[No name given]
On June 16, 1892, I found a gall of very striking appearance, from its deep scarlet color, on Rhus microphylla, in New Mexico. The gall is of peculiar shape and resembles a cluster of many thickened leaflets massed together. At a casual glance, it might be mistaken for the fruit of the Rhus, which is in clusters and orange-colored but very different in form.

Gall.--Average diameter, 15 to 25 mm; length (on twig), about 20 to 30 mm. Galls luster-like, irregular in shape, sometimes, rounded, cocks-comb-like in appearance, springing from the small stems which shoot out laterally from the twig or branch, or terminal portions of latter. Consisting of irreglar massed clusters of many aborted, deformed, greatly thickened and fleshy leaflets springing from the side stems; surrounding the twig or branch but not attached thereto, dark scarlet-red in color on all surfaces exposed to the sun, the under side when no so exposed being annually greenish and always lighter than the upper or exposed portions. Inside portions green. External surface of the gall extremely irregular in outline, the fleshy leaflets arranged in irregular cocks-comb-like groups more or less pointed apically, the groups of leaflets longitudinally creased, appearing as though formed of many little columns set side by side and soldered together, much resembling groups of certain columnal crystals.

The fleshy groups of leaflets contain irregular cavities within them. These, when opened the following spring, revealed only small pale brownish bodies attached to the walls inside. It may possibly be an acarid--perhaps a phytoptid.

Aculops arizonarhus Keifer, 1966
Host: Rhus microphylla
Relationship: The mites apparently deform flower bud.