Favorite plant in the garden, but don't know what it is

I think it's a tree Peony but would need a closer shot of the foliage and woody stems to be sure.

Here's a pic of the upright form of tree peony.

http://i1294.photobucket.com/albums/b609/WestAussieforeva/uprightformtreepeony_zps9bfc1e1a.jpg

If it is a peony you are very lucky, they are beautiful. They don't like to compete for space or sun so make sure you don't plant anything too close to it. The "tree" form is quite slow growing. They are quite drought tolerant too and don't like the soil to be constantly moist. After flowering is the best time to fertilize. It also would benefit from pruning the inside branches so it is trained to more of an open habit.

Hi MrsBee, it's quite tolerant of most soils. The bush peonies are also beautiful and come in a huge range of colours. To my mind they are better than roses! (no thorns )

Peonies are all deciduous. Also their flowers increase in size as the plant matures, unless they get too much shade. However tree peonies have a leaf divided into three points at the end, whereas yours comes to a single point. This might be the rootstock that has sprouted and taken over the grafted plant. This can happen when the grafted peony has not been planted deeply enough. Tree peonies, you see are grafted onto herbaceous peonies. Either way, you still have a very attractive plant.