Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Pachypodium habitats
"Rapanarivo et al." measured the pH levels for the soil in half the sites of "Pachypodium" endemic to Madagascar. The pH ranges approximately from 3.5 to 7. Strictly acid soils that had a pH level of 3.5 to 5 were preferred by "Pachypodium brevicaule", "P. cactiples", "P. densiflorum", "P.eburneum", and "P. rosulatum". The next level, acid to basic soils, with a pH between 4.5 and 7 were suitable for "P. lamerei" and "P. rutenbergianum". On soils with a neutral pH level of 7, "P. meridionale" inhabit. "P. sofiense" grows on calcareous soils but also in acid soils with a pH level of 4. "P. lealii" grows on outcrops of granite in fairly fertile, acid soil.