citrus relatives

Botanists classify the true citrus as follows: family..............RUTACEAE
                                                                           subfamily........CITROIDEAE
                                                                           tribe.................CITREAE
                                                                           genus...............CITRUS
I haven't made special efforts to locate citrus relatives - there are too many, and I don't have enough space to grow them! However, I do have the species described below, plus, of-course, Poncirus trifoliata.

The Wampee is native to Southern China where it is cultivated for its fruits. There are sweet and acid forms. Although only distantly related to citrus, the species are mutually graft compatible.

Fruit cut open to reveal the internal soft flesh and occasional seed. Seeds have a thin skin covering green cotyledons, and a dark brown tip - the Chalazal spot.

I have only recently obtained this plant, but I now believe it is probably not a true Clymenia. Although said to have originated from Clymenia seed, the fruit apparently points to a Kumquat or Kumquat hybrid.
Clymenia is botanically either very close to citrus, or even a true citrus. My plant has not yet produced flowers or fruit, is about 40cms tall, and grafted on to citrange rootstock. Leaves are fairly long and slim, rather like a clementine.
The fruit of Clymenia is said to be sweet, but internal structure distinct from all other citrus varieties.

Also known as 'boxthorn' this evergreen shrub is native to Southern China.
Although known to be graft compatible with citrus, my plant is growing on its own roots - either a seedling or cutting.
After many years, it has just produced its first flowers, which are only about 4mm across.
The fruit is said to be a small, round, black berry,
looking somewhat like a blackcurrant.

This is a very distant relative. The only obvious connection to citrus is that the tiny fruit are, like citrus peel, covered in oil glands.
Thamnosma is a small herbacious perennial, or sub-shrub, from California. My plant has flowered after about 3 years from seed, sent to me from Rancho Santa Ana Botanic Garden. The whole plant has a distinctive pungent smell when brushed against, giving its common name of "Turpentinebroom". Also known as "Desert Rue".

Seeds sent to me from Australia.
The classification of Glycosmis seems very complicated and not fully understood or agreed by different botanists.
My plants are two year old seedlings, about 6" (15cms) high. They show no sign of any trifoliate leaf characteristic.