Hernández M., Terrazas T., Delgado Alvarado A., Luna Cavazos M., Los estomas de Myrtillocactus geometrizans (Mart. ex. Pfeiff.) Console (Cactaceae): variación en su área de distribución, Revista Fitotecnia Mexicana, 2007, 30(3):235-240, doi: 10.35196/rfm.2007.3.235
The study compares stomata in 49 samples from 20 Mexican populations. All material had parallelocytic stomata, with subsidiary cells arranged parallel to the guard cells. Stomatal density was greater in the apical stem region, while size was similar in the two stem regions compared. Population variation was associated with latitude and some soil properties.