Citrus ichangensis Seeds | Ichang Papeda
LATIN NAME: Citrus ichangensis
COMMON NAME: Ichang Papeda
Plant Profile
No other evergreen citrus takes cold like this one. The ichang papeda grows in mountain valleys in south-central China where winter frosts are long and hard, and it survives temperatures that would strip the leaves from any lemon or sweet orange. That single quality, rather than any virtue of the fruit, is why plant breeders have kept the species in circulation for a century and why its name appears in the pedigree of rootstock after rootstock. The name itself commemorates the stretch of the Yangtze where Western botanists first met the plant.
It grows slowly into an open, airy small tree with slender branches and short thorns, and in a hard winter it can shed part of its foliage without harm. The habit is loose rather than dense, which makes the tree look sparse next to a mandarin.
The most useful single character of the species is its petiole. The leaf stalk is flattened into a wing that may be longer and broader than the small blade sitting at its tip, so a shoot looks as though it carries little more than a chain of green paddles. The papeda wing is what gives the group its name.
The papedas are the wild, cold-tolerant citrus of southern Asia, and this species is generally treated as the hardiest of them. Genetic work places it close to the base of the group from which the cultivated citrus are thought to have been assembled, and its diploid count of eighteen chromosomes follows the family pattern. Its fruit is a small round berry with a thick yellow-orange rind that is knobbly rather than smooth, and the pulp vesicles hold oil droplets, which is what gives the juice its acrid, almost medicinal burn.
The commercial importance of the ichang papeda rests on its value as a parent of rootstocks. Seedlings of the species graft readily with lemons, mandarins and oranges, they tolerate soils that are too heavy or too wet for some of the traditional stocks, and they pass a useful degree of cold tolerance to the scion above them.
The better-known quality of this stock is its behaviour in the presence of citrus tristeza virus, the pathogen that has destroyed millions of trees on sour-orange roots. Ichang papeda and its hybrids withstand infection without the decline that kills a sour-orange-based tree, so where the virus is present the stock has been used deliberately.
Science & Biotechnology
Citrus bitterness comes from limonoids, the triterpenoid derivatives that accumulate in the fruit and seed, and work on this species contributed two compounds named directly for it, ichangin and ichangensin, to the chemical literature on the genus. The intensely sour, oily pulp of the ichang papeda is the visible expression of that chemistry. The peel oil is built around limonene, with smaller amounts of other monoterpenes, and the rind yields far more oil per fruit than a sweet orange because there is so much more rind.
Uses & Benefits
This is a breeding citrus rather than a dessert one, and the kitchen treats it accordingly. The zest, grated or dried, gives a clean bitter-citrus lift to a marinade, and the whole fruit used sparingly in a preserve or a chutney gives the sourness of a lemon with a long bitter finish. The juice is too harsh to drink alone but performs well in a syrup or a dressing where sugar is present. Its closest aromatic relative in cultivation is the Japanese citrus grown for its zest, which genetic work treats as a hybrid with this species as one parent.
Growing from Seed
Fresh citrus seed is best sown soon after it is cleaned, because the seed loses viability quickly when it dries out. Use a free-draining mix of two parts loam-based compost, one part sharp sand and one part finely sieved leaf mould, sow the seed about fifteen millimetres deep in a deep pot, and keep the pot at a steady mild temperature with the surface just damp; the seedlings of this species emerge with unusual vigour and often several sprouts come from one seed, since citrus seed is frequently polyembryonic. Prick the strongest shoots into individual pots once they show four true leaves, and grow them on in bright light with protection from the hottest midday sun.
Move the young tree into a larger pot each spring until it reaches the size you intend to keep. Water deeply and then allow the top of the compost to dry before watering again, because citrus roots rot in permanently wet soil; a container standing in a saucer of water is the commonest way to lose a plant. Feed from spring to late summer with a citrus fertiliser that includes trace elements, especially iron and magnesium, and stop feeding through the winter. Prune only to shorten the leggy growth or remove crossing branches, since the species naturally builds an open crown. Keep the tree above freezing in winter, with as much light as an unheated glasshouse or a cool porch can give; the plant tolerates more cold than most citrus, but wind and wet cold together will still mark the leaves. Watch for scale insects and red spider mite in a closed winter space, and treat the leaf undersides early.
Our Take
This is a citrus to grow as a parent, a stock or an experiment, not as a dessert fruit, so start it in a deep container and keep it for the season when you want cold tolerance in a graft. Growers building a hardy collection should add the aromatic Japanese citrus Citrus junos beside it, and the small-fruited calamansi, Citrus microcarpa, which will crop in a pot while the papeda is still filling its own. If you want a bitter orange for marmalade instead, the sour orange, Citrus aurantium, is the better kitchen tree.
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