Edited 5/3/14 (removed info on anemone nemorosa, and created separate post for it)
Japanese genus name for camellia:
We have just one in our Garden, standing above skimmias in Area D; this year it started blooming early April.
Here on the web of the rare plants nursery in Eugene, Oregon, I found its japanese name: ‘Shiragiku’ (scroll down below pictures)
And here a longer description from the Backyard Gardener: ‘Purity’ bears rose-form, double flowers in shimmery white. Slow growing, upright to spreading shrub or small tree with age. Oval, glossy, leaves and profuse winter to spring blooming flowers in milder climates. […]