PONCIRUS trifoliata

A small, very spiny tree, of interest in being a hardy, deciduous near-relative of citrus fruits. Because the twigs and spines are green, the plant appears green even when it is leafless. Produces attractive, supposedly fragrant, white flowers in spring, which develop by fall into yellow fruits resembling small oranges. These sour, fruits are often considered inedible. Used commercially as a rootstock on which to graft other citrus fruits. Considered cold hardy to about -15°F, its range of cultivation can be extended into zone 5 if it is planted in a sheltered location and perhaps given some extra protection.