The first time I encountered tropical lettuce, or Indian lettuce (Lactuca indica), was when I was exploring a rooftop garden in Fujian province of rural southern China. It was the middle of the day in the middle of the summer, and here was this beautiful lettuce exposed to full sun in a raised bed with less than six inches deep of relatively poor soil. I was amazed that this plant which was obviously in the lettuce genus, was alive at this time of year at all, not even wilting the least bit under the oppressive summer sun in the sub-tropics, and growing with what appeared to be weak care. Needless to say, but my attention had been caught.
Tropical lettuce is native to southeast Asia, and both India and China have a long history of incorporating tropical lettuce into their agriculture and cuisine. Its native zone is not contained to just the tropics though; the plant is native to very cold temperate Helongjiang in the north, and all the way down to tropical Guangdong in the south.
Researching the current literature on tropical lettuce I discovered discrepancies in its species classification. Lactuca indica is briefly mentioned in Edible Leaves of the Tropics by Franklin W. Martin, and from this source the description and photo of the leaves of the plant matches my own observations, which indicate a tall, erect and heat tolerant lettuce that is bitter in taste. Plants for a Future database has a very similar description as well, although the picture they have of the plant appears similar to a much more wild type of lettuce with a serrated leaf, which is reminiscent of a relatively common weedy species in many places of North America. Adding to the confusion there are Chinese sources that use several different species names.
Tropical Lettuce in Chinese is Youmaicai (油麦菜). Looking up the scientific name using that common name will give one the result of Lactuca sativa var. longifolia or Lactuca formosana on various Chinese websites and books, and interestingly the latter is a reference to Taiwan in Portuguese, i.e. Formosa. Oddly enough, this appears to be one of those rare cases that researching with a common name may yield more accurate results than the scientific name.
Growth Habit & Strategies
Tropical Lettuce is a low maintenance biennial that will thrive in gardens with rich soils. The World Vegetable Center, Plants for a Future, ECHO, and the book Oriental Vegetables all list tropical lettuce as a perennial. However, in my own observations I have not seen a tropical lettuce plant live more than 2 years.
Like other lettuces, it will grow fine during the cold dry season here in Southwest Florida, and in summers in cool temperate climates. In the subtropical dry season it will grow more vigorously and taller than most veggies common in the garden, as much as 4 feet in height, and can grow up to 8 feet tall in the summer. Where tropical lettuce really shines though is in its ability to tolerate hot summers in tropical climates. It also has the potential to naturalize in sun patches in Agroforestry systems in early succession; a valuable trait generally, but especially in subtropical and tropical gardens. I have recently transplanted some plants into a sun patch in my forest garden and they seem to be thriving with little irrigation. It needs to be kept in check when planted with tender Brassicas however because its growth rate outpaces the latter, or it ought to have its own low maintenance bed devoted to the crop solely on the edge of Zone 1 and 2 (between row crops and agroforestry systems).
Seed propagation of the crop is elementary and done easily. In fact, if tropical lettuce goes to seed and disperses naturally via wind it will no doubt pop up in fertile soil in the surrounding area. Once the plant is finished setting seed it can be cut back and will resprout, which is among its many unique virtues. Propagules can also be rooted from cuttings of the mature stems very easily for asexual propagation.
Medicinal and Nutritional information
Tropical Lettuce contains substantial amounts of vitamin A, vitamin B1, vitamin B2, vitamin C, along with some calcium, iron and other nutrients. The strong flavors of the greens indicate a plant with high nutrient density. Tropical lettuce is also used as a folk medicine for anti-inflammatory, antibacterial, and other medicinal qualities in Asia
When eaten fresh, the leaves are more bitter than a traditional lettuce (Lactuca sativa). Tropical lettuce works well in a stirfry or boiled with other greens. The Chinese mainly stirfry it with garlic and a bit of soy sauce as shown in the picture below. It can be eaten as a fresh green balanced with other strong flavored foods and dressings.
A great choice for the subtopics and tropics, it is also a crop that merits use and experimentation with in many garden contexts, and use in diverse local food systems.Tropical lettuce is a great low maintenance crop that will grow year round in frost free climates, and self sow itself into abundance in the garden. If it starts to spread out too much just dig some out and share it with the community! Try checking out and enjoying the bounty of Tropical Lettuce this growing season.