Q: We have some oak trees at the school where I work that drop a plethora of acorns. However, the caps on these acorns are like “mop-heads”; they have bristles sprouting all over the cap. What kind of oaks are these?

A: The trees are probably sawtooth oak, ^Quercus acutissima^. It is native to Asia and has been planted in numerous places for ornament and to attract wildlife. Unfortunately, the “mop-head” acorns sprout so vigorously that this invasive tree has the potential to drive out native plants. The native chestnut oak would have been a better choice of your school’s landscape architects.