Whether they show their appreciation with candy, flowers or dinner at a restaurant this Mother's Day, many Americans will also say thanks with a greeting card.

The search starts at least a week before Mother's Day every year, as shoppers crowd around card displays across the country, looking for the sentiment that is just right for the mother -- or mothers -- in their lives. Mother's Day is the third biggest holiday for card buying in the United States, according to Deidre Parkes, a spokesperson for Hallmark, a leading American producer of greeting cards. "It ranks behind Christmas and Valentine's Day, which means that Americans will send about 150 million Mother's Day cards this year," says Ms. Parkes.

For Hallmark, that means lots of advance planning. "We usually work 12 to 18 months in advance," Deidre Parkes says. "I believe Mother's Day 2006 has already been planned, and a lot goes into that. We look at trends and all kinds of things going on, so we make sure that by the time they hit the stores we've got the appropriate products."

In recent years that has come to mean expanding the very definition of motherhood. "The family is changing from mom, dad and the 2.5 kids to extended families, step families, adoption," says Ms. Parkes. "So Hallmark now makes cards for stepmothers, birth mothers, as well as adoptive mothers, even for fathers who have played the role of both father and mother. Mother's Day is all about recognizing the role of that person who has been a nurturer, so that role doesn't necessarily fall to just a biological mother. It can extend to all kinds of different people."

An American woman named Anna Jarvis is credited with conceiving the idea for Mother's Day. She wanted a special occasion to honor her own mother. In 1914, Mother's Day became an official holiday to be observed yearly on the second Sunday in May. By the 1920s, Deidre Parkes says Hallmark had begun making greeting cards for the occasion. "We have continued to do that over the years," she says, "to respond to the demand of consumers who say, 'Maybe I don't verbalize to my mother that I love her, but I want to put it into writing and share it with her.' We did a survey recently and asked mothers what they do with their Mother's Day cards, and there was a tremendous number, maybe 80% of mothers, who say they keep every Mother's Day card they get."

Deidre Parkes describes the first Mother's Day cards as simple and traditional, saying little more than just 'Happy Mother's Day.' While they may have gotten more elaborate over the years, they continue to be heartfelt expressions of thanks. "Our humor line doesn't perform very well, compared to the sentimental cards," says Ms. Parkes. "We have this saying at Hallmark that you make Dad laugh and you make Mom cry at Mother's Day. The cards are really there to just tell Mom you love her, because I don't think we do that enough."

Mother's Day cards have become more multicultural over the years. "In the Hispanic and Latino population, Mother's Day is the number one holiday," Deidre Parkes explains. "They hold their mothers in very high regard, and this day is very important to them. We've expanded our Spanish language cards so we're sure to have cards for that market. We also have African American cards, so we make sure there is pretty much something for everybody."

Hallmark also sells Mother's Day cards outside the United States. "Mother's Day is celebrated in different forms around the world," Ms. Parkes notes. "Not all of them celebrate the second Sunday in May, but there is in almost every country a day set aside to honor mothers."

And how well are traditional greeting cards competing with the Internet, where you can press a few buttons and send your mother an E-mail greeting? Deidre Parkes believes that while electronic communication is great for a quick message, it cannot take the place of a card that arrives by mail or is delivered by hand, read, then tucked away in a drawer to be taken out and appreciated years later.