Amaranth greens contain glycine betaine (trimethylglycine)

Several botanical families of plants accumulate betaine (i.e., glycine betaine, trimethyglycine, or TMG). One of the major ones in use for human food purposes is the amaranthaceae family. (https://hungary.pure.elsevier.com/hu/publications/betaine-distribution-in-the-amaranthaceae) Here's the Encyclopaedia Brittanica summary of the primary food species in the amaranthaceae family:

Food crops in the family include the various forms of beet (Beta vulgaris, including garden beets, chard, sugar beets, and mangel-wurzel), lamb’s quarters (Chenopodium album), and spinach (Spinacia oleracea). Some species—namely, Inca wheat, or love-lies-bleeding (Amaranthus caudatus), red amaranth (A. cruentus), and quinoa (Chenopodium quinoa)—are high-protein pseudo-grain crops of interest to agricultural researchers. Quinoa in particular, touted as a health food, grew in popularity worldwide during the early 21st century.

https://www.britannica.com/plant/Amaranthaceae

In the past few posts, I've discussed the TMG contribution to various regional diets from inclusion of beet, spinach, amaranth seed, and quinoa seed. But I only recently learned of the use of amaranth greens for human consumption. They deserve a post, for they are eaten commonly in several places outside Europe and North America.* The leaves of amaranth are reported to accumulate glycine betaine. (http://www.sciencedirect.com/science/article/pii/S0003986196997313)

Amaranth, despite being once a major foodstuff in southern Mexico, fell into disuse after the arrival of the Spaniards:

Grain amaranth was as important as corn and beans to the Aztecs, who believed that it gave them supernatural powers and used it in ceremonies involving human sacrifice. Some 20,000 tons of the seeds were delivered by Aztec farmers in annual tribute to their emperor, Montezuma.
In Aztec rituals, amaranth was mixed with human blood, formed into cakelike replicas of Aztec gods and fed to the faithful, a practice the Spanish regarded as barbaric and a mockery of Christian communion. Hernan Cortes put a stop to it by condemning to death anyone found growing or possessing amaranth.

http://www.nytimes.com/1984/10/16/science/ancient-forgotten-plant-now-grain-of-the-future.html (The article is from 1984, so we haven't reached the future yet.)

And it wasn't just human blood they were mixing into the little amaranth figurines, it was purportedly blood from human sacrifices--at least according to a video program called Ancient Grains Series: Amaranth (https://www.amazon.com/Amaranth/dp/B00VZ4A8D4) that I just watched--which would explain the Spaniards' revulsion. But humans no longer eat amaranth seeds in conjunction with murder victim blood, so it seems like amaranth should be poised to become a major foodstuff again.

Amaranth greens are popular in many parts of Asia, Africa, and the Caribbean, where they are usually eaten stewed, which is a great way to coax TMG out of its leaves. For some reasons, people in the USA just want to use amaranth greens in salads, though. (http://www.appalachianfeet.com/2010/05/10/how-to-grow-and-use-amaranth-greens-wrecipes-sources/, http://www.today.com/food/sick-kale-amaranth-next-super-green-try-6C10658383) (Why don't Americans like to consume liquid from boiled food? That subject calls for its own post.)

In Jamaica, they call amaranth greens "callaloo," which can get confusing because callaloo is also used as an appellation for other greens as well as for the dish made with amaranth and/or other greens. (https://realjamaica.org/what-on-earth-is-callaloo, http://www.africanbites.com/callaloo-jamaican-style/) Despite multiple research papers on autism epidemiology out of Jamaica in the past few years, I can't find any estimates of autism prevalence there, so I can't say whether high Jamaican consumption of amaranth greens is protecting them to any extent from autism spectrum disorders (per my hypothesis).

* According to various wikipedia articles, kañiwa, sessile joyweed, chenopodium album (i.e., lamb's quarters or bathua; popular in north India), celosia argentea var. argentea (Lagos spinach, soko yokoto, or cresta de gallo; popular in India), and epazote are also food/herb crops within the amaranthaceae family and so are likely to be good dietary sources of TMG. I have no experience with eating any of them, and all seem to be relatively unknown in most of the more economically developed countries. I list them in hopes that some researchers will read this and investigate how much glycine betaine these foods might be contributing to the diets of the people who eat them, but I won't do individual posts on them.