Is Taiwan far enough off-shore to be genetically isolated?
I think it would be very difficult for species from the mainland to reach Taiwan by natural means, perhaps not impossible. Most likely any original citrus species that were brought to Taiwan were brought there by humans - the Chinese. (With the exception of C. tachibana which was probably indigenous to either Taiwan or Southern Japan, or perhaps both)
The island of Taiwan is 160 km (about 100 miles) away from mainland China. And probably most of the citrus types did not even exist on the coast of China in that area before the Chinese civilization came, with the exception of kumquat.
There are about one thousand endemic plant species in Taiwan, meaning they exist only on Taiwan, not the mainland. So this would seem to indicate some degree of natural genetic isolation.
According to one ancient text, mandarin oranges could be found growing in the wild on the island of Hainan by around the year 1000 AD, though it is unlikely the species originated there. (
Edward H. Schafer, Shore of Pearls: Hainan Island in Early Times, University of California Press, Berkeley, 1970 )
They probably escaped into the wild from human cultivation.
Forestry Bureau held a "Return of the Nansho Daidai Sour Orange" event at the hiking trail entrance of the Daping Forest Road of Jiali Mountain in Nanzhuang Township, Miaoli County. Planting of the Nansho Daidai Sour Orange took place at the event, where it was also pledged that this citrus species will be brought back to its place of origin (this citrus, named after Nanzhuang, is an endemic plant of Taiwan and is now on the verge of extinction in the wild). It is the hope that this act can help restore the forest ecosystem in the foothills of Taiwan and promote the development of green economy in the mountain village communities.
The Nansho Daidai Sour Orange (Citrus taiwanica Tanaka & Shimada) is a citrus species in the Rutaceae family endemic to Taiwan. It was first documented that the plant was discovered in 1926 by Japanese botanists in Miaoli's Nanzhuang Hongmaoguan, present-day Penglai Village in Nanzhuang Township, and was therefore named "Nansho Daidai Sour Orange." However, with the development and utilization of the foothill forests, the Nansho Daidai Sour Orange almost become extinct in its original discovery site, and it has been listed in the IUCN Red List as a Critically Endangered species due to its rarity.
The Penglai region in Nanzhuang is the traditional living area of the Saisiyat people. According to Gen Chih-You, a Saisiyat elder, the Saisiyat name for Nansho Daidai Sour Orange is gadayou (meaning "food prepared by mother"). The citrus has been an important plant for the Saisiyat since ancient times, since the fruit is both a snack and also has medicinal and ceremonial applications. Elder Gen recalled that when he was a child, whenever he had a cold, the family elders would grind dried Nansho Daidai Sour Orange into a powder for him to take as medicine. It was a must-have plant for general healthcare used by every Saisiyat family in the early years when medical treatment was not readily available.
According to the Forestry Bureau, the fruits and leaves of the Nansho Daidai Sour Orange have a strong fragrance, while the juice has a distinctive sour taste and a slight bitterness. The fruit's unique flavor makes it very suitable for processing and consumption. Furthermore, the wood of the orange tree is extremely fine in texture, and according to literature, it was considered the best wood for making pipes, knife handles, and other delicate wooden tools in the early days.
The fruits were tested for the development of essential oil extraction, dessert-making, and tea and beverage preparation, all with amazing results. At the event, the Hsinchu Forest District Office presented a "pound cake with Nansho Daidai Sour Orange frosting" made using the juice and "Nansho Daidai Sour Orange peel nama chocolate" made using the orange peel syrup. The unique refreshing scent and tangy sweetness of the Nansho Daidai Sour Oranges greatly impressed the guests who tasted the delicious treats. It is hoped that the local tribal communities of Nanzhuang will create specialty products with Nansho Daidai Sour Oranges, as it would not only help with both species preservation and the economy, but also bring a wonderful flavor experience to the people of Taiwan.
"Return of the Nansho Daidai Sour Orange": Forestry Bureau Partners with the Saisiyat to Restore Taiwan's Endemic and Rare Plants
from Taiwan, January 29, 2021
https://www.forest.gov.tw/EN/forest-news/0067054(It should of course be noted than Nansho daidai was already a cultivated variety in Japan in old times, before being found by the Japanese botanist growing in the wild in Taiwan. It was valued in Japan as an ornamental because the fruits continue to hang on the tree for a long time, sometimes up to several years)