Everyone has Maeng Da on their strain list, but is it the same? Is it the famed mutation of the regular kratom leaf into horn shaped leaf tips which allegedly gives Kratom the Stimulating effects. Is it just random leaves on the tree, or is it the entire tree? There are lots of random pics of individual leaves, but never more than one or two together. The "Maeng Da" legend appear to be a hoax, as there is no evidence.
The main alkaloid in Kratom is Mitragynine, and this alkaloid trades off with 7-hydroxymitragynine within the plants leaves. The plant does not appear to produce any 7ohm, but rather converts it from Mitragynine. Green leaf, which is dried indoor to prevent oxidation is said to be high in Mg with only trace amounts of 7ohm. Leaf that is dried in the sun turns red from oxidation and is said to be high in 7ohm. The blending of these two yields what is known as Bali, quite possibly the first Indonesian blend ever. This is the most famous blend in Indonesia today.
A comparison of these alkaloids: the ceiling on Mg seems much lower than 7ohm and it seems like you top out quick. Then comes a weird eyeball muscle paralyzing phenomenon called the wobbles where your eye muscles get extremely weak and your vision blurs as your eye struggles to focus. One study hooked rats femoral nerves to electrodes and were given Mg until the twitch stopped. One could assume that this weakness (wobbles) is caused by this "nerve blockade" effect from Mg. Mg also feels like it has a longer half life and the next burn could put you back into the wobbles in seconds even with a much lower quantity than before.
High 7ohm means a much higher ceiling, as you can use twice as much red than you can with one of the greens and lasts roughly half the time. This powerful opioid agonist is what scores so high on mu opioid receptor chart at 15 times the score of morphine, and 10 times that of Mg. This alkaloid feels like a classic opiate, and is the main opioid element in Kratom.
All of the other effects that you get are merely from the other 24 known alkaloids in different concentrations and ratios, all synergizing together, along with some "placebo effect" . Im sure there are some regional, geographical differences in the plant, but I don't think it's anything major: nothing that you could categorize, like being Thai, or Indonesian. The alkaloid profiles are probably pretty similar throughout kratom growing regions, unlike the sophisticated diverse world of cannabis cultivation.