List.AddRange Has Some Invalid Arguments

I want to create a list of flowers (for example) that conform to a predefined IFlower interface as below.

public interface IFlower
{
    string colour { get; }
    int petals { get; }
}

public class Rose : IFlower
{
    public Rose()
    {
        string[] colours = new string[]{ "Pink", "Orange", "Red", "Crimson", "Cerise" };
        Random random = new Random();
        colour = colours[random.Next(0, 4)];
    }

    public string colour { get; set; }

    public int petals
    {
        get { return 8; }
    }
}

public class Daisy : IFlower{
    public Daisy()
    {
        string[] colours = new string[]{ "White", "Yellow", "Purple" };
        Random random = new Random();
        colour = colours[random.Next(0, 2)];
    }

    public string colour { get; set; }

    开发者_运维知识库public int  petals
    {
        get { return 18; }
    }
}

public class Flowers
{
    public List<Daisy> Daisies
    {
        get
        {
            List<Daisy> items = new List<Daisy>();
            items.Add(new Daisy());
            items.Add(new Daisy());
            return items;
        }
    }

    public List<Rose> Roses
    {
        get
        {
            List<Rose> items = new List<Rose>();
            items.Add(new Rose());
            items.Add(new Rose());
            return items;
        }
    }
}

The problem is, when I run the following code to create the concatenated list:

    public List<IFlower> Flowers
    {
        get
        {
            List<IFlower> output = new List<IFlower>();
            output.AddRange(Daisies);
            output.AddRange(Roses);
            return output;
        }
    }

I get the error:

The best overloaded method match for 'System.Collections.Generic.List<IFlower>.AddRange(System.Collections.Generic.IEnumerable<IFlower>)' has some invalid arguments

The Roses and Daisies tokens must each refer to an instance of a class implementing

IEnumerable<IFlower>

So I guess that one or both of them refers to something else.