Prague Citsuma may be the best citrus available that combines cold hardiness and taste. Surviving 3°F (-16°C) 1, and 1°F (-17°C) 2 without damage, making it hardy in Zone 7a, and perhaps Zone 6b

Ripe fruit are sweet without the bitterness of Poncirus.4 Leaves are small and widely spaced. The leaves vary between trifoliate, bifoliate and unifoliate. Branches are thin and slightly pendulous.

The origin of Prague maybe unknown. B. Voss received it from the from greenhouses ITSZ from Prague. ITSZ is the abbreviated name of the Institute of Tropical and Subtropical Agriculture. This is a Faculty of Agriculture University. It is suggested that it came from Russia. It is possible it could be the Chinese chimera Hormish, but small fruit of Prague are not pubescent.

Chimera
While in a hybrid all the cells are genetically identically the same, 'a chimera is a plant composed of two or more genotypes in the layers that make up the shoot tip' 3 For Prague, based on taste and appearance, the fruit cells are Satsuma, and the stem tissue and part of the leaves are from Poncirus, possibly Dragon.

Woody plants have three dividing cell layers at the growing tip. They are named L1, L2, and L3. L1 is the source of the exterior of the stem and the top of the leaf. It makes the epidermis, stomata, and sacs in fruit. 4 In the diagram, the green color are the cells from Poncirus, L3

It is probably a chimera 2 for the following reasons
1) Quality of the fruit
2) Appearance of the leaves in the winter indicating a mixture of genotype.
The L1 epidermis
L1 sub epidermal layer
L3 corpus, inner layer, center of leaf, also vascular bundle. L3 is poncirus

Schmidt (1924) presented the “tunica-corpus” concept to describe the stratified appearance of the cell layers in the shoot apical meristems of flowering plants. Most dicots have three distinct apical cell layers (L1, L2, and L3) that remain independent from each other...In citrus fruit, both the juice sac and pericarp epidermis originate from L1; L2 ordinarily produces seeds, segment walls, the hypoderm, and the mesocarp of pericarp; while L3 develops into the vascular bundle

According to the “tunica-corpus” theory, a plant chimera is a mosaic in which genetically different cells exist in the shoot apical meristem that gives rise to cells that develop into organs of the plant.5

Pictures taken in January 2020 showing the yellow in the center of the leaves from Poncirus cells.

Virginia Fruit Grower Video