Originally introduced from China and Korea, in some areas of southern USA thickets of Poncirus trifoliata are now growing wild. However, I have been often been asked by US visitors to this web-site, where they can find fruiting plants of this species, outside the normal range of citrus. Living in England, this is difficult. My only personal knowledge is of some plants I have seen at Harvard University's  Arnold Arboretum in Boston.
4. There are currently two plants of Poncirus trifoliata 'Flying Dragon', and two of the standard form, listed at the JC Raulston Arboretum, North Carolina State University, Raleigh, North Carolina. Click for map of beds. Poncirus trifoliata are in beds E19b, W15, JG1 & L08
Also note the nearly hardy
Citrus ichangensis in bed E13, the Citrange in A10 and the Citrumelo in A11.
The arboretum's web-site has some excellent pictures of both the 'Flying Dragon' variety, and the standard form. Search the image database, and J.C. Raulston's slide collection.
3. Arnold Arboretum, Boston, MA. See map. From the main entrance take the Linden Path to the newly planted Shrub and Vine collection.There is a group of plants on the right just where the path passes the corner boundary of the arboretum.  (On the map, this is near the letter 'L' in 'Linden'.) See  my photos here.
Do you know of fruiting plants of Poncirus trifoliata in USA, well outside normal citrus regions?
Send me ' mike
(at sign)homecitrusgrowers.co.uk '  exact details of the location of other specimens in USA, and I will list them here.
Please ensure they are mature fruiting plants, and publically accessible. Any description or pictures will be welcome.
Click here for my pages listing Poncirus locations in Great Britain and some other European countries.
page re-built 11th March 2009,  24th Dec 2010 & 3rd Jan 2011
5.The North Carolina Arboretum lists three Poncirus trifoliata plants in its database

JC Raulston Arboretum
Washington Arboretum Poncirus trifoliata
1.The database of the New York Botanical Garden  lists several plants.
2. I have been told that there are several specimens in the Asian Collection at the National Arboretum in Washington, DC.
6. Quote from Arthur Lee Jacobson's website: "One in Portland, Oregon, at the Bishop's Close Elk Rock garden is nearly 15 feet tall, over 19 feet wide and its trunk 8 inches thick in 2003" Photos here.
7. Seattle, WA. Also from Arthur Lee Jacobson's website:"You can view a Hardy Citrus at the Washington Park Arboretum; it grows north of the path that leads from the Azalea Way parking lot (east of the covered lookout above the pond), and has dark yews as a background."
8. New Jersey. Dmitri & Olga Matievski e-mailed me with photos of the Trifoliate Oranges at The Frelinghuysen Arboretum, near Morristown, N.J. For exact locations of the standard and Flying Dragon forms, click the map here. Both are in the parking area.
Frelinghuysen Arboretum Poncirus
9. Pennsylvania. Again from the Matievski's - this time at Longward Gardens, north-east of Kennett Square, PA.
A visitor to this website recently sent me this picture of the arboretum's Flying Dragon plant.
Frelinghuysen Arboretum Poncirus
Frelinghuysen Arboretum Poncirus Flying Dragon fruit
Frelinghuysen Arboretum Poncirus fruit
Longward Gardens - Flowering Trifoliate Orange
Longwood Gardens - Poncirus trifoliata flower detail
For exact location, click here.