*3.3. FE-SEM-EDS Analysis*

Figure 5 shows the morphology and elements detected by EDS analysis. Differences between hypodermal and cortical element concentrations were observed. *Astrophytum asterias* has the highest concentration Ca (49.53%) and Al (0.87%) in the prismatic crystals of the hypodermis, whereas in *Echinocactus texensis*, hypodermis showed the lowest concentrations of Ca (5.08%) and Al (0.15%), but the highest of Si (25.34%). No traces of Mg, K and Si were detected in *Astrophytum asterias* spherulites (Figure 5F), but traces of Si (0.91), K (0.79%), Mg (0.17%) were detected in *Ariocarpus retusus* subsp. *trigonus* (Figure 5H).

**Figure 5.** SEM images and EDS spectra for stem tissues of Cacteae species. (**A**,**B**) *Astrophytum asterias* (TT1020), prisms in hypodermis. (**C**,**D**) *Echinocactus texensis* (TT1021), amorphous silica bodies in hypodermis. (**E**,**F**) *Astrophytum asterias*, spherulite in cortex. (**G**,**H**) *Ariocarpus retusus* subsp. *trigonus* (TT1005), spherulites in cortex. The white square on images was the area used to analyze the elements. Bar is 10 μm in A, E, G; 1 μm in C.
