These dear little trees are planted in large terracotta pots outside our greenhouse and seem to survive the winters quite happily.

The calamondin is a shrub or small tree growing to 3–6 m. The plant is characterized by wing-like appendages on the leaf petioles and white or purplish flowers.
The fruit of the calamondin resembles a small, round lime, usually 25–35 mm in diameter, but sometimes up to 45 mm. The centre pulp and juice is the orange colour of a tangerine with a very thin orange peel when ripe. Each fruit contains 8 to 12 seeds.
Calamondin is a citrofortunella, an intergeneric hybrid between a member of the genus Citrus (in this case probably the mandarin orange) and the kumquat. There is also a variegated mutation of the regular calamondin, showing green stripes on yellow fruit
It is native to the Philippines and surrounding areas in southern China, Taiwan, Borneo, and Sulawesi. Calamondin is ubiquitous in traditional Filipino cuisine. It is used in various condiments, beverages, dishes, marinades, and preserves. Calamondin is also used as ingredients in the cuisines of Malaysia and Indonesia.

“Wikipedia”