C#中如何查找Dictionary中的重复值

//initialize a dictionary with keys and values.   
Dictionary plants = new Dictionary() {   
    {1,"Speckled Alder"},   
    {2,"Apple of Sodom"},   
    {3,"Hairy Bittercress"},   
    {4,"Pennsylvania Blackberry"},   
    {5,"Apple of Sodom"},   
    {6,"Water Birch"},   
    {7,"Meadow Cabbage"},   
    {8,"Water Birch"}   
}; 
   
Response.Write("dictionary elements........
");
         
//loop dictionary all elements  
foreach (KeyValuePair pair in plants) 
{
    Response.Write(pair.Key + "....."+ pair.Value+"
");
} 
   
//find dictionary duplicate values. 
var duplicateValues = plants.GroupBy(x => x.Value).Where(x => x.Count() > 1);
 
Response.Write("
dictionary duplicate values..........
");
 
//loop dictionary duplicate values only           
foreach(var item in duplicateValues) 
{
    Response.Write(item.Key+"
");
}