Polystichum dudleyi is confined to coastal central California. Hybrids with P . californicum are relatively frequent where these species occur together. These hybrids would key here but, unlike P . dudleyi , they are less divided and have aborted sporangia. The sterile diploid hybrid with P . munitum is also frequent in areas of sympatry. It is indistinguishable from P . californicum except for malformed sporangia and chromosome number (W. H. Wagner Jr. 1973).