Trifoliate orange (Poncirus trifoliata, synonym Citrus trifoliata), is a member of the family Rutaceae, closely related to Citrus, and sometimes included in that genus, being sufficiently closely related to allow it to be used as a rootstock for Citrus and to readily hybridize with all Citrus species.
The plant is a fairly cold-hardy citrus (USDA zone 6) and will tolerate moderate frost and snow, making a large shrub or small tree 4–8 m tall. Because of the relative hardiness of Poncirus, citrus grafted onto it are usually hardier than when grown on their own roots.
Poncirus trifoliata is recognizable by the large 3–5 cm (1.2–2.0 in) thorns on the shoots, and its deciduous leaves with three (or rarely, five) leaflets, typically with the middle leaflet 3–5 cm (1.2–2.0 in) long, and the two side leaflets 2–3 cm (0.79–1.18 in) long. The flowers are white, with pink stamens, 3–5 cm (1.2–2.0 in) in diameter, larger than those of true citrus but otherwise closely resembling them, except that the scent is much less pronounced than with true citrus. As with true citrus, the leaves give off a spicy smell when crushed.
The fruits are green, ripening to yellow, and 3–4 cm (1.2–1.6 in) in diameter, resembling a small orange, but with a finely downy surface.
The cultivar "Flying Dragon" is dwarfed in size and has highly twisted, contorted stems. It makes an excellent barrier hedge due to its density and strong curved thorns. Such a hedge had been grown for over 50 years at Oklahoma State University in Stillwater, and is highly student-proof. The plant is also highly deer resistant
The fruits of Poncirus trifoliata are widely used in Oriental medicine as a treatment for allergic inflammation, although there is no evidence such treatments are effective.
- Gerald Klingaman. "Plant of the Week. Hardy Orange or Trifoliate Orange. Latin: Poncirus trifoliat". University of Arkansas. Division of Agriculture.
- Green Deane Hardy. "Hardy Orange".
- Zhou H.Y., Shin E.M., Guo L.Y., Zou L.B., Xu G.H., Lee S.-H., Ze K.R., Kim E.-K., Kang S.S., Kim Y.S.,"Anti-inflammatory activity of 21(alpha, beta)-methylmelianodiols, novel compounds from Poncirus trifoliata Rafinesque." European Journal of Pharmacology. 572 (2-3) (pp 239-248), 2007.
- Media related to Poncirus trifoliata at Wikimedia Commons