Mary-marry-merry merger

In most of the United States and Canada // is merged with /æ/ and with //. For 57% of American and Canadian speakers Mary, merry and marry are homophones. In others marry is distinct (9%) and in others merry is distinct (16%). Outside of North America (and also for 17% of Canadian and Americans) all three phonemes are distinct.

Since there is no distinction between // and // it can be said that in American English there is no phoneme //, only //. However the diphtong [ɛə] is heard when a syllable ends with /r/, as in square [skwɛər]. Phoneticians say that // followed by /r/ at the end of the syllable is realized as [ɛə]. In other words, broad notation is /r/ and narrow notation is [ɛər].

Most American dictionaries write marry as /ˈmæri/ because it's easy to go from /ˈmæri/ to [mɛri], but it would be impossible to know if [ˈmɛri] stands for /ˈmæri/ or /ˈmri/ in those places that make the difference (26% of North Americans).

Merriam-Webster's Learner's Dictionary (MWLD) uses three symbols (narrow notation). /ɛ/ for "dress", /e/ for "scary", "carry" and "cherry", and /eɚ/ for "square".

Homophones or minimal pairs
The following words are homophones in some accents and minimal pairs in others
 * /eə, æ, /: Mary - marry - merry;
 * /eə, æ/: hairy - Harry;
 * /eə, /: airer - error; fairy - ferry; vary - very;
 * /æ, /: Aaron - Erin; barrel - beryl; Barry - berry, bury; parish - perish;