It's a big oval creature, whether you consider it a shrub or tree is up to you. They tend to grow 10-20' tall and often two-thirds as wide. On the eastern end of Long Island they bloom late April. As you can see the white five-petaled flowers are fantastic, and this year very prolific.
When the flowers pass it begins to leaf-out with the three-part leaves from which it gets it's specific epithet, trifoliata. Ultimately it's a gnarly, thorny thing that requires a lot of maintenance to be kept really picture perfect but just the same I love it.
The thorns and hardy acidic fruit make it a fun conversation piece here in our Zone 6b or 7a. It's safely hardy in Zones 6-9. Native to China and Korea it was introduced to the US around 1850.
It's one of those rare trees that are fun to observe in every season. The spring flower is sweet and wonderful. The stems of green and serious thorns mix in well with the summer landscape while still giving it plenty of character. Not to mention the great fuzzy fruit that begin to form. By fall they will mature yellow, loaded with lots of seeds and very, very sour. According to Dirr if you let the fruit set for a few weeks it develops a nice acidity, as well as the peel worthy of being candied, but can't say I have ventured that far with my love of this small tree. Perhaps I will experiment with a few of these fruits this fall.