Thursday, November 18, 2010

Question for the Hive Mind: Crassula rupestris?

I either need the help of a Crassula expert or a person who is not a Crassula expert but has the ability to talk about them in such a way that everyone will think s/he is correct. I don't particularly care which.

The reason is, I need someone to settle for me, once and for all, whether this is Crassula rupestris or Crassula perforata.

It was identified as C. perforata when I first got it, but then I've subsequently seen plants called C. perforata that looked very different, with much larger leaves and longer internodes (distance between leaves):

The above pictures could be different varieties of the same species; I saw a picture on line that made me think C. perforata 'Tom Thumb' was a possible ID for this plant, but I don't remember where it was, so I can't link to it. And, unfortunately, this page at Dave's Garden says that 'Tom Thumb' is a variety of C. rupestris, not C. perforata.

I've been confused about this for quite some time, but it's suddenly important that I figure it out, because whatever the plant in the top photo is, I'm going to write about it for the next plant profile. (UPDATE: Which has now been written.) So I have to settle on an ID before I can start, because search-and-replace on blog posts is a pain. Please help.


Pat said...

Neither from the pictures at Tropicos and Linnaeus' descriptions from 1781:

C. rupestris

foliis connatis ovatis integris glabris, corymbo supradecomposito

C. perforata

foliis opposito-perfoliatis ovatis, caule simplici

Caules simplicissimi, teretes, rubicundi, sesquipedales, nudiusculi

Folia opposita, perfoliata, cordata f. ovata, acutiuscula, margine aequali, laevia, superne sensim minora, radicalia approximata.

The amount of nitrogen and light makes such a difference to succulent plants. My Crassula volkensii got a bit too much nitrogen and now its trying to be a Jade Tree.

Peter said...

The problem is that crassulas interhybridize so readily AND they can look very different from different growing conditions THAT it can be difficult to know for sure. I would suggest yours is C. rupestris. Another way to look at it is to use a common name like Jade Necklace (which is also a c.v. name) for all the hybridized C. perforatas and C. rupestrises.

CelticRose said...

I'm leaning more toward C. rupestris. Your plant looks nothing like the C. perforata that I've got on my windowsill (my plant was positively identified by the folks on CactiGuide).

From what I'm seeing online, C. perforata has more angular leaves (my plant's leaves are almost sharp enough to scratch my skin), while C. rupestris has rounded leaves similar to your plant.

I'd suggest putting the question to the folks on CactiGuide and benefitting from their experience.

Sentient Meat said...

I grow a few variations of C perfoliata and several of rupestris. From the leaves, I would definitely guess... between the two choices... your plant looks much closer to rupestris than to perfoliata. Usually C perfoliata has larger leaves and C rupestris has smaller leaves, but I have a large-leaf variety of C rupestris from Huntington Botanical Gardens.

If memory serves, the last time I was puzzling this out, I learned the biggest difference is in the flowers. C perfoliata has weedy, almost inconspicuous flowers, whereas C rupestris has more compact flowering stalks and what I think of as more typical Crassula flowers: star-shaped, plain-but-pretty white-to-pink flower (similar to jade plant C ovata or C 'Springtime' flower).

Sentient Meat said...

Oops, that should be 'perforata' not 'perfoliata'.

Unknown said...

The best place to check Crassula IDs on the net is here for future reference. It does help to know which names youe are looking for first though, as this site has no browse feature. I do think what you have is C. rupestris of some sort, though the colouring is very pale, due to the plant being indoors.

Here is a link to C. rupestris and its three sub-species:

Also the hybrid C. 'Tom Thumb' (which has a lot of rupestris in it)

And here is C. perforata to compare. C. perforata is quite variable, but is nearly always a larger plant than C. rupestris and the flowers are quite different as well.

I hope this is useful to you.