Unargueably the best yellow of the Herbaceous peony species (that is, the ones that die back to the ground each year, as opposed to the Tree peonies) Paeonia mlokosewitschii is another of the beauties from the Caucasus region. As always, the shade of colour is variable from paler to darker, and I've assembled a comparative shot with petals of 3 of my plants, including the darkest and lightest, although it doesn't really get the true colours. The first 2 flower photos are the yellowest that I have; my bike approves of their shade. First bloom here 29 May this year.
This is a rarity in the Peony genus in having only one name!! and the only synonym is a variation in the spelling.
Mloko's native environment is on sunny slopes in hardwood forests. It seems also to have a penchant for moisture and unless irrigated is likely to have problems with dry climates. Plants in my gardens are best in about 3 to 4 hours of mid-day sun and shaded by trees for the rest of the day. They do almost as well with a bit less sun, and are adequate in the woodland bed, where even a single flower illuminates an area. They are desperately slow-growing in the unirrigated open field, taking at least 2 years longer from seed to flower than in the other locations.
The foliage is more purple than red when emerging and, depending on the plant keeps some degree of purple tinge in the leafs into the flowering period as well as purple stems long into summer. Leaves on some plants change colour throughout the season, and may have quite a bluish tinge. Seed pods and seeds add great colour in late summer, as with all the Caucasus species.
This species has the interesting property of accepting pollen from a lot of other species, and it hybridizes readily. This means that plants grown from seed collected in gardens is liable to result in plants with non-yellow flowers, and if you are dead set on a yellow flower you need to ensure that any plant you buy has flowered true; inexpensive young seedlings may not be a good buy. Nonetheless there are some very attractive plants resulting as can be seen from these last 2 photos.