Why is helleborine sometimes called 'chatterbox'?

I found out now, thanks to the question about the etymology of chatterbox, that 'chatterbox' is another name for helleborine (something I've never heard of). A helleborine is apparently

an orchid growing along streams or ponds of western North America having leafy stems and one greenish-brown and pinkish flower in the axil of each upper leaf

What could possible be the etymology for this?

The Chatterbox Orchid Epipactis Sabine Frankfurt, also known as Helleborine, Stream Orchid is so called because of a fancied resemblance to an open (talking) mouth...

(the Rolling Stones logo for comparison).