Are orchids C3, C4, or CAM plants?

[Jayfar]

Originally Posted by epiphyte78

If anybody is interested here's a write-up I recently posted on CAM Orchids.

That link broke, but I found the current link with a google site search:

Which Family Has The Most CAM Species? - Xeric World Forums

[samarak]

Thanks to those who posted links to papers on C3/C4/CAM - it's a topic I've also been reading on lately and think is fascinating. I'll be reading the Silvera paper tonight!

I've been under the impression that most C4 plants were identifiable by the distinctive Kranz anatomy (bundle sheath cells, where CO2 may be fixed away from oxygen to avoid photorespiration). That doesn't answer the original question directly, but may provide some more search terms.

Steve

[hcastil3]

ah, I love these posts, they make my day, I'm so happy to learn on all these things, now the alternation of generations of plant life cycles are a great thing to read up on too, if anyone gets bored.

like the microgametogenesis, megagametogenisis, and so many many things!!!

[dabblin-n-orchids]

One time in which i know for a fact carbon fixation should influence culture is leafless orchids. let me be more specific actually: ghost orchids. this does not obviously hold true for mycoheterotrophs.

Ghost orchids utilize the CAM pathway. that is why it is essential that they dry out by the end of the day. this is because the roots are the photosynthetic organ AND the water and nutrient absorbing organ and they can only do one thing at a time. when the roots are wet they can't absorb CO2 and convert it to malic acid. so if they stay wet all night they will be unable to photosynthesize the next day. there is an article out there somewhere about it. i'll try to track it down.

EDIT: this might be it: Photosynthetic Carbon Assimilation in a Shootless Orchid, Chiloschista usneoides (DON) LDL

[OliverSparrow]

The biochemical division between C3 and C4 is not a yes-no thing, as the relevant enzymes are generally present at some level. What makes for C$ is the leak architecture, and that orchids do not have. I recall reading that CAM had evolved many times separately within different orchid clades.

[naoki]

I know this is an old thread, but if someone is really interested in this topic, Arditti's book, Fundamentals of Orchid Biology has a table summarizing which species are C3 and/or CAM. In the text, he said that there were 2 cases (Arundina graminifolia & Arachnis Maggie Oei) where data suggest the possibility of C4, but the results do not conclusively support C4. So even though some orchids grow in environment where C4 would be optimal, there aren't any C4 orchids discovered yet. Unlike CAM, I don't think C4 has repeatedly evolved.

Also, some CAM plants are facultative CAM (especially under cultivation). C3 is more energy efficient, so when there is plenty of water, facultative CAM plants use C3 pathway. Phal is an example, I believe.

If you have only strict CAM orchids, you can basically ignore the daytime air humidity (i.e. very low RH in the day time isn't so much of a problem).

Here are some examples from the Arditti's table. There are cases where a genus contains both C3 and CAM (e.g. Coelogyne). When I put the species name, there are only a few examples, so it may not be generalizable to the genera.

C3:
Catasetum fimbriatum
Coelogyne massangeana
Coelogyne mayeriana
Coelogyne rochussenii
Most Cymbidium (but C. lowianum is reported to be CAM)
Cypripedium acaule
Eulophia keithii
Havernaria platyphylla
Most Oncidium
Paphiopedilum
Spathglottis plicata
Vanda tessellata (surprising)

CAM capable:
Aerides odoratum
Angraecum sesquipedale
Arachnis
Ascocentrum ampullaceum
Bulbophyllum gibbosum
Calanthe vestita
Coelogyne cristata
Cyrtopodium paranaensis
Dendrobium taurinum
Laelieae
Phalaenopsis
Pleurothallis ophiocephalus (not conclusive)
Thuria marshalliana
Vanilla

[OliverSparrow]

I've posted here before, but nothing happened. Better luck this time, I hope.

I'm not going to dig for papers, so this is from memory. About a third of orchids have CAM capacity, almost all of the epiphytes. the trait evolved at least ten times, perhaps twenty. That's because all the "plumbing" is there for CAM in a standard C3 plants, and all that needs to change is some reshuffling. To the best of my knowledge, no orchids are C4. All but a few desert chenopods have krantz anatomy - cell sheaths around their leaf vascularisation - and so far as I know there are no orchids which show this.