It means the other leaves fell or were broken off
It's more rare than the 4-leafed clover, of course, but not as lucky I assume. You can make up your own rules; it's not like it makes any difference.
luckier than four leaf clover
A four leaf clover is good luck..... a 3 leaf clover is a weed. Not to be confused with Shamrock which is one of our national symbols.
The clover signified Second Corps, as First Corps was a full moon, third corp, a diamond, fifth a Maltese cross, sixth, a roman cross, eleventh a crescent, and 12th a five pointed star.