Merging overlapping polygons into one polygon

[JulieLuetzelschwab]

I have a polygon feature class of weeds.  Each polygon represents the area of one weed species.  There are many places where there are polygons on top of polygons because the area has several different weeds growing in the same area.  I need ONE polygon for these overlapping areas and ONE field listing all the weed species in that area so infested acres are not double counted.  So one area may have 4 overlapping polygons representing weeds A,B,C, and D.  I want one polygon with one field attributed with A,B,C,D.  And ideas?

[JonathanBaarda]

You could try a spatial join on the different polygon classes, then make a new field calculated from the joined attributes, e.g

if field a = yes, then new field = new field + "A"

[JulieLuetzelschwab]

Thank you for the suggestion.  I tried it and it only joined to one other polygon, not all 4 that are overlapping.  I also tried IDENTITY and it does the same thing - it only attaches to one other polygon, not all 4 that are overlapping.  UNION won't let you union a layer to itself but I could make copies.  But with IDENTITY and UNION it still only attaches to one other overlapping polygon.  If I do an IDENTITY four times it still attaches to the same polygon, it doesn't know to look for a polygon it hasn't attached to, if that makes any sense.  Another option is to split out this feature class into about 20 feature classes with each one being a unique weed species, then merging them back together and then concatenate all the species code fields into one field.