Mother's Day Etiquette -- what is expected?

Who is expected to participate in Mother's Day -- you know, send cards, candy, flowers, phone calls?

I thought it generally was children of the Mom, and the father of the children to the Mom. Even a step-father to the Mom of his step kids. And maybe from a wider range of people when a woman is newly a Mom, like her friends, siblings, etc.

To be nice, I have intermitently sent greetings to single moms if I knew they had the blues or were having a rough patch in which they could have benefited from an acknowledgment of what nice mothers they were to their kids.

Who, typically, is supposed to participate? Do brothers and sisters send greetings to their sisters who are mothers every year? If you were casually dating someone, would you expect him to celebrate the day with you?

What is the accepted practice?

(There is a weird story behind this question. I have my own take on it, but I wanted to get a range of responses before I'm sure my understanding is correct)

right out in front of everybody

he and the kids always do something special. We also send cards to our moms and our one remaining Grandma. :hi:

1991. She was 82 and yes she always got something from myself and our daughter, her same sake, on mothers day