Selling fresh produce only when it's in season locally is increasingly rare at Hong Kong markets, and the phenomenon is closely linked to globalised trade patterns. Reliable, reasonably priced, refrigerated sea transport, combined with cheaper air freight in recent years, has ensured that as soon as oranges, pears, apples and grapes become unavailable in southern hemisphere countries, such as Australia and South Africa, the produce of northern regions, from Israel to North America, will step in.

In consequence, looking forward to a couple of months of gorging on a particular seasonal delight is an enjoyment denied to younger generations accustomed to year-round availability.

But some popular fruits do remain strictly seasonal, longans being an obvious example.

See also: For the foragers of Hong Kong, countryside is a veritable banquet

Almost as soon as Hong Kong's midsummer lychee binge finishes, the first longans mark the start of early autumn; they are among the most widely cultivated fruit trees in the Pearl River Delta region.

The word "longan" is an anglicisation of the Cantonese loong ngan ("dragon's eye"). In the Malay-speaking areas of Southeast Asia, where the fruit originated, they are known as mata kucing ("cat's eyes"); when the light brown fruit is opened, the translucent pulp and black seed core make it clear where such names come from.

The most commonly cultivated variety, Dimocarpus longan, falls within the same botanical family as the lychee; to the inexperienced eye, the trees are indistinguishable. While longan trees can grow up to 12 metres in height, most are kept pruned to a manageable level for fruit picking. Extremely frost-sensitive, longans are usually grown in semi-sheltered areas of villages, and are almost unknown at higher altitudes.

Most longans sold in Hong Kong markets originate from either southern China or northern Thailand and Laos, where over the past 20 years extensive agri-business enterprises have been established. Consequently, longan production has soared, and the market season in major import destinations, such as Hong Kong and Singapore, has lengthened considerably.

Increased production has also kept prices reasonably stable, and longans are actually cheaper, in real terms, than they were a decade ago. Critics take note; globalisation does eventually bring some benefits.

Lychees and longans can be canned. While the tinned variety are usually over-sweetened, with an insipid, watery flavour, compared with the fresh fruit, they nevertheless offer a year-round "taste of home" to émigré Chinese communities all over the world.

From the 1950s onwards, a plate of chilled canned lychees or longans, routinely served with vanilla ice cream and wobbly wedges of violently coloured jelly, appeared at the end of Chinese banquets all over Southeast Asia. While these obviously imported dishes demonstrated luxury and affluence on the part of the host, to some they also offered a palpable reminder of an ancestral homeland that, for political reasons, most overseas Chinese could never hope to visit during that tumultuous period.

Dried longans  can be found all year round in shops that specialise in Chinese dried foodstuffs. Dehydrated longans are used in medicinal teas and Chinese herbal soups. Like lychees, longans are believed to be "heating" and are included in tonic preparations intended to restore the body's internal balance, especially if a person is too "cool", and suffers various afflictions derived from that condition.

For more on Hong Kong history and heritage, go to scmp.com/topics/old-hong-kong