P. lamerei has a wide, graceful leaf. This plant had grown tall enough that it was hard to get it through the door jam when it had to be moved in for the winter, plus that made it too tall to see and appreciate the pretty tops of the branches, so I chopped it off one Spring and waited patiently; eventually it put out three crowns, and these two developed into new branches.
P. geayi has a more rigid, longer, slender, pointed leaf with a white line down the middle.
As you can tell, these pictures were taken outside during warm weather, as it happens, a couple of years ago. Those same pachys are much taller now and are still doing well. Fat plants, as a rule, and this species in particular, are pretty forgiving and will be around a long time if you take care of them. They love to be outside in filtered sunlight during the warm months and need to be brought in during the winter. Mine tend to lose some or all of their leaves during the winter inside, but once outside new green leaves burst forth quickly. I have noticed that the older they get, the fewer leaves they drop. Feed them maybe once a month during the summer, water about once a week, and they should do just fine.
I bought these plants as little seedlings at The Living Desert back when it was in Bee Cave (“A Good Place to buy Cactus,” August 24, 2014). They were maybe six inches tall with a trunk about as big as my little finger, and now they are about five feet tall and had been way taller than that when I cut them off. I bought them back in the days before I bothered to keep track of purchase dates, so I can only estimate that they are at least ten years old, maybe closer to fifteen. They are really fun when they are small to use in dish gardens because they look like tiny little palm trees and lend themselves to interesting landscaping in the dish. I don’t have any pictures of them as babies; you’ll just have to use your imagination.
And babies grow! Eventually they like their own big pot, but they can stay in a large pot for basically the rest of their lives and be happy. So if you purchase one, be advised that you are signing on for a long-term relationship.
Your tree will become a member of the family! And that’s not a bad deal, I must say.