Feast After Famine: What's Latin for 'I Don't Know?'

I have a life-list problem: I want to identify every plant in my garden by its Latin name but it turns out, I don't even know all their common names. 

I've been mooning over the garden the past few weeks and every time someone comes to visit, I take them on a loop tour around the house and round the gigantic maple in the back. If you were a mosquito on the back of our dog, you'd hear multiple conversations that go like this: 

Friend: "Ooo, that's pretty. What is it?"

Me: "Isn't it beautiful? I don't know."

Friend: "I like that one too. What's it called?"

Me: "I don't know."

The garden overflows with "I don't knows." 

On a lunchtime tour of the yard, I found nine flowers in bloom, only five of which I could name. I deadheaded the pink peony then it surprised me with a second round of flowers. The pink and white gumpo azaleas are easy enough to identify. My mother bought me the clematis on Mother's Day and gave me the astilbe from her garden years ago. 

But what to make of the tall white flowers on the red-leafed plant in the shade by the garage? My mother gave me those too but neither of us can remember what they're called. And the gorgeous periwinkle flower that stands tall along the drive? I picked it up at the Del Ray Farmers Market last year and it's spreading quite nicely.  

My mother bought me a beautiful pink clover-like flower that we ooh-ed and ahh-ed over in a garden in Old Town. And a friend gave me a different, though equally brilliant, pink flower that rises from soft, silvery foliage that resembles lamb's ear but isn't.

So, what are they all called? Seems like such a shame to say, "I don't know."

Luckily, I don't have to any longer. I asked friends, family and strangers on the Internet the other day and got answers to all but one: the red-leafed white flower. Want to help me solve the mystery? Or, at the very least, tell me how to translate "I don't know" into Latin?