How to let a method accept two types of data as argument?

this is somewhat the same question as I've asked some time ago:
How to let a method accept two types of data as argument?

Yet the current situation differs.. a lot.

Take this:

public FormResourceSelector(Dictionary<string, Effect> resourceList, string type)
 

Alright, nothing wrong with it.
Now I try to run this:

FormResourceSelector frs = new FormResourceSelector(AreaEffect.EFFECTS, "Area effect");
 FormResourceSelector frs2 = new FormResourceSelector(DistanceEffect.EFFECTS, "Distance effect");
 

Both AreaEffect and DistanceEffect (custom classes) derive from Effect.

public class AreaEffect : Effect
 {
     public static Dictionary<string, AreaEffect> EFFECTS = new Dictionary<string, AreaEffect>();
     ...
 }
 

For some reason I get the following error while making the new FormResourceSelector instance:

Argument 1: cannot convert from 'System.Collections.Generic.Dictionary<string,SCreator.AreaEffect>' to 'System.Collections.Generic.Dictionary<string,SCreator.Effect>'  
 

at:

new FormResourceSelector(AreaEffect.EFFECTS, "Area effect");
 

I suspect the dictonary being a harass, but I don't really know how to fix this.

Thanks for helping me out :).

~ Tgys

EDIT: Easiest would be to allow input of both Dictionary and Dictionary as resourceList in the first code snippet I've given.

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