Oak Single my oak tree has produced acorns every year is producing a round balls cut open looks like a fruit one seed ? it is healthy just this weird things single and as many as 4 in a cluster They could be oak galls. look at http://www.ento.psu.edu/extension/factsheets/gallsOnOak.htm http://www.gtcd.org/cgi-bin/content/content.cgi?db=content&uid=default&ww=on&id=314&view_records=1 http://bexar-tx.tamu.edu/HomeHort/F1Column/2004Articles/DEC5.htm they are the tree's reaction to insects and usually do not harm ...