Fruit and branches of Citrus trifoliata
Do not worry — Botany Photo of the Day has not decided to change its content to science fiction! Today’s photo may look like a creative writer’s vision of unexplored planets, but it in fact shows the fruit and thorny branches of Citrus trifoliata.
The fruit of Citrus trifoliata may look like an orange (the common name for this species is trifoliate orange), but it certainly doesn’t taste like one. The fruits are edible, but are intensely sour and bitter, and are best used for adding pectin to jams that feature tastier fruit. A Citrus trifoliata lemonade recipe advises to “take a barrel of water, a barrel of sugar and add one sour fruit” (UofA Division of Agriculture). Some sources do not consider this species to be a member of Citrus. Many botanists use the synonym Poncirus trifoliata (L.) Raf., considering trifoliate orange to instead be the closest relative to the genus Citrus (and the only species in Poncirus). For this article, I will stick to Linnaeus’ original name, as this is the one accepted by The Plant List.
Whether you think trifoliate orange is a Citrus or not, this species is undeniably important to the lemons and oranges that we love to eat. Citrus trifoliata (pdf) makes an excellent rootstock for other Citrus species. It is very cold hardy (withstanding temperatures well below freezing), so other Citrus species grafted onto the rootstock can produce trees with tasty fruit that survive in cold climates. Arguably, the most significant advantage of a Citrus trifoliata rootstock is that it confers resistance to the citrus tristeza virus, the most economically-damaging Citrus disease. Trifoliate orange also hybridizes freely with other citrus, and has been used to make numerous crosses including: citremons (with lemons), citranges (with sweet oranges) , and citrumquats (with kumquats).
Aside from Citrus trifoliata‘s contribution to our morning orange juice, it is also an interesting ornamental species. Its young green branches are dense and bear stout, 5cm-long stipular spines. The overall effect of the plant’s habit is that it can be considered an evergreen for aesthetic purposes, though it is actually deciduous. Trifoliate orange can be pruned into an impenetrable hedge or low boxwood-type wall. The twisted-stemmed cultivar ‘Flying Dragon’ makes an unusual specimen tree. The young shoots of Citrus trifoliata are stiff and have a triangular cross-section, and the leaves are trifoliate (composed of three leaflets), shiny and dark green. They turn a buttery yellow before dropping in the autumn. The flowers are white with pink stamens, hermaphroditic, and have a typical, citrus smell. These give way to globose (round) fruit that measure 3-5 cm in diameter. Technically, the Citrus trifoliata fruit is a modified berry termed a hesperidium, which has a tough leathery rind encasing a fleshy interior composed of separated sections.
Note: Citrus trifoliata is naturalized in the American southeast, and forms dense thickets that are impenetrable and displace native species. Planting trifoliate orange in these areas is not advised.
As Citrus trifoliata is ‘naturalized’ in the American southeast, what is it’s native range?
Incredible! Thanks for the post!
I have two of the Flying Dragon cultivar. They both survived -17F this past winter and the larger of the two flowered.
I’ve made marmalade out of the fruits and it is edible but not a favorite! The rind also has a gummy substance when cut that sticks to everything and can only be removed with nail polish or the like.
Citrus trifoliate is of Chinese origin . As per patches in the South East , spent many an hour hunting deer and turkey in Florida in my younger days and never saw a volunteer patch . Granted they will from large patches from trees that are planted as for some strange reason there is no parental alleopathy to their own seedlings , this is rare as most woody plants eschew they own offspring . I have seen Citrus sinensis become a little invasive but never to the point of establishing patches of resistance . Somehow I think the point of it being invasive is a bit exaggerated , Citrus has been in production the parts of Fl, TX and LA for over 100 years and presumeably many homestead would have had trees of some sort or another , considering that C. trifoliate does not freeze would suggest that what is taking place is patches derived from old rootstocks that have resprouted after the chosen graft was frozen out . It should be remembered that C. trifoliate has recalcitrant seeds and have a very short life span and will quickly degrade and die upon exposure to the elements if ideal conditions are not available .
I have managed to root several P. trifoliate suckers from rootstock from potted limes and lemons. It is fairly easy to root. It can then be used for rootstock if you want to try your hand at grafting.
I was first introduced to this plant as a proposed hedge around military bases. It was given the common name “pain and terror.”
Mystery solved! Or at least I’m now closer to the explanation of a mystery. I had a potted citrus that eventually died. I hauled it, pot and all, to the unheated garage until I could discard it in the spring and repurpose the pot. It must have experienced temps of close to zero on occasion repeatedly through the months of January and February. But in the spring green shoots came up from the soil line. I kept one shoot and trained it to a six-foot standard. It is probably a Citrus trifoliata. Thanks for the information.
” …flowers…have a typical citrus smell.” Really? I have read this in many sources yet I have never smelled much of anything from the many trees I have sampled.