Stemata or Stemmata: How To spell?
The word Stemata is misspelled against Stemmata, which is plural of "Stemma"
Stemmata has double "mm" is mispronounced as "m"Remember double 'MM' in between the strings ste & ata which should not be misspelled with single 'M'
Wrong Spelling:  ste-m-ata  Correct Spelling:  ste-mm-ata 
Explore spell check of Stemmata to spell without errors.