Pass a constrained type to a method
public static List<ListItem> ListItemListFromEnum(Type t)
{
    ...
}

public static List<ListItem> ListItemListFromEnum(Enum e)
{
    Type t = e.GetType();
}

public static List<ListItem> ListItemsListFromEnum<T>() where T:Enum

public static List<ListItem> ListItemListFromEnum(Type t)
{
    if (!t.IsEnum)
    {
        throw new ArgumentException("Type must be an enumeration", "t");
    }
}

public static List<ListItem> ListItemListFromEnum<T>()
{
    if (!typeof(T).IsEnum)
    {
        throw new ArgumentException("Type must be an enumeration", "t");
    }
}

public static List<ListItem> ListItemListFromEnum(Type t)
{
        if (!t.IsEnum)
        {
            throw new ArgumentException("The type passed in must be an enum type.");
        }

        // ...
}