I don’t know if this has happened to you, but I have picked up a plant at the nursery marked, “succulent” or “houseplant”, got it home to find out that I already had this variety. One genera that trips me up is crassula and sedum. These are two genera that are really large and contain numerous varieties. Some are very different and some are super similar.
One reason that it is sometimes difficult to identify crassula and sedum is that when you buy your plants at the nursery that are little plant babies. Many of the differentiating factors aren’t noticeable until the plants mature. A Crassula ovata does not develop its woody stem and tree like characteristics until it grows for over a year.
Sedum preaeltum – Seán A. O’Hara from Berkeley, CA, USA [CC BY 2.0 
Crassula Ovata – Forest and Kim Starr [CC BY 3.0
Crassula:
- Broadleaf Evergreen
- Woody Stem
- Grows into Tree or Shrub
- Leaves emerge in pairs, almost symmetrical
Sedum:
- Herbaceous Perennial
- Grows in clumps or mounds
- Leaves form Rosettes
For more plant identification check out this post on succulent identification and Latin for plant lovers.
Can you clarify for me whether leaves stacking in a particular way differentiates crassula from sedum?
Just in my observations, the crassula puts out two leaves from the middle of the previous set of leaves, and then they alternate direction. The Sedum puts out leaves sort of all over and tends to grow in more of a clump with less of a pattern. But like all plant identification, this is not a rule or anything. The only true way to tell similar plants apart is by their flower.