DH just always has.
No big presents (or expectations of them on my part), although some years he's surprised me with jewellery etc... I remember that when I was pregnant with DD, I told him that I couldn't wait to get chrysanthemums for mothers day and so he's always bought me some and written me a beautiful card. My kids are 6, 4 and 6 months and the big ones made me the most beautiful handmade cards and gifts and DH gave me my 'mums, my card and a sleep in! I got a lovely card from my mum to me and my MIL gave me chrysanthemums as well (so did my bestie) - those close to me are well aware of my love of that flower
I would feel sad if he didn't acknowledge me on mothers day - he acknowledges my mum, his mum, my gran!