Crassulacean Acid Metabolism

[epiphyte]

There are quite a few families listed on the Wikipedia page on Crassulacean Acid Metabolism (CAM). Can you guess which family has the most CAM species?

[drzoidberg1]

Well since it's named for the type of plants that use this type of metabolism I'm gonna say Crassulaceae.

[Tyrone]

Isn't this something succulents use to open stomata at night. It sort of like a stored up photosynthesis that operates at night, when other plants have shut down sugar production. It's like a reverse photosynthesis that desert plants use so they can absorb sunlight during the day but keep the stomata shut so they don't dehydrate. Then at night when things have cooled down they open the stomata for gas transfer and make sugars then. Normal plants make sugars while the stomata are open during the day. So Aloes, Crassulas, Cacti and Euphorbias would fit into that category. Don't know if Hoyas would. They're rainforest plants and can operate like normal. Agave's may.

Best regards

Tyrone

[fastfeat]

Well since it's named for the type of plants that use this type of metabolism I'm gonna say Crassulaceae.

Well, I'm guessing that the metabolism was discovered as occurring in Crassulaceae, but I'm not certain that family would necessarily therefore have the most species... I remember learning about the process, but I've got no definite answer to the quiz. I just got outta a two-week "unplanned vacation" at a couple of SoCal's graybar hotels, so I'll leave it to others to answer the riddle.

Happy 4th to all.

[DoomsDave]

Yeah, this is kind of mind-blowing

how the plant inhales during the day, but doesn't exhale till night

try that you phys-fit-fanatics . . . .

whoo ee

[epiphyte]

The correct answer is...the Orchidaceae! Here are a few references...

- 1983, Winter et all, Crassulacean Acid Metabolism in Australian Vascular Epiphytes and Some Related Species

This is the reference that first introduced me to the concept of CAM. From it I got the impression that there are relatively few terrestrial succulents in Australia. However, approximately two thirds of the epiphytic/lithophytic orchids studied were CAM plants. Orchids with thicker leaves generally had a greater degree of CAM...as did those from more exposed habitats. Heat plays an important role so lower elevation orchids tend to be more CAM than those at higher elevations.

After a brief breakdown of the number of species in the largest terrestrial succulent families...the authors concluded with the following..."Thus, from the standpoint of species numbers it may be that more CAM plants exist as epiphytes in tropical and subtropical rainforests than exist in arid terrestrial habitats. If this is so, we should perhaps reconsider the validity of the commonly accepted notion of a "typical CAM plant", characterized as a cactus-like stem succulent growing in a desert environment."

Incidentally, I was quite surprised when several years later I ran across an entire book on Australian succulents. It wasn't much of a surprise though when I browsed through it and found that quite a few of the plants included were orchids.

- 1989, H. Griffiths, Carbon Dioxide Concentrating Mechanisms and the Evolution of CAM in Vascular Epiphytes

This paper provided a table with the following numbers...

Orchidaceae / 30,000 species / 20,000 epiphytic species / ~60% CAM species

Cactaceae / 1,800 species / 120 epiphytic species / 100% CAM species

Bromeliaceae / 2,500 species / 1,144 epiphytic species / ~50% CAM species

Crassulaceae / 1,000 species / 5 epiphytic species / 100% CAM species

- 2010, Luttge, Ability of Crassulacean Acid Metabolism Plants to Overcome Interacting Stresses in Tropical Environments

This is the most recent paper that I've found. Here are some of the numbers it provided...

Orchidaceae - 9500 CAM species

Cactaceae - 1500 CAM species

Bromeliaceae - 1250 CAM species

Wikipedia puts the Crassulaceae at 1400 species so it seems that the Cactaceae is the second most CAM rich family at around 1800 species.

Basically, even though an epiphytic orchid might live in a rain forest, its micro-habitat on the tree can possibly be considered xeric...depending on where on the tree it's growing. Orchids on the outer branches tend to be more exposed to sun and wind so they'll dry out faster than orchids in crooks or low down on the trunk.

Here's where it gets interesting. While the large majority of epiphytic orchids occur in rain forests...quite a few have radiated into dry forests. It's the same concept with Cactus and other succulent families. The large majority of Cactus occur in drier habitats but a few have adapted to wetter habitats. For example, here's an in-situ photo of Miltonia flavescens growing with Epiphyllums and what looks like a Ric-Rac Cactus.

To try and illustrate this concept I created this diagram...

Cactus and Orchid Moisture Continuum by epiphyte78, on Flickr

The proportion is probably off...and I'm not exactly sure in which type of habitat Cactus or epiphytic orchids have the most species. If somebody wants to give a whack at it feel free to PM me for the MS PowerPoint file.

As faulty as my diagram may be...it helps illustrate that if you purchase a random cactus...chances are pretty good that it comes from a drier habitat. On the other hand, if you purchase a random epiphytic orchid...chances are pretty good that it comes from a wetter habitat. But!...in absolute terms, in comparison to Cactus...there are just as many, if not more, epiphytic orchids that are from "drier" habitats.

Where it gets difficult is that there are books on miniature orchids, several articles on fragrant orchids and 100s of orchid monographs...but no single reference that consolidates the epiphytic orchids from dry forests. I've scoured 100s of references and come up with a reasonably comprehensive list. Still haven't quite decided how much accompanying info to include for each species.

But if I had to pick one single reference to recommend...it would be the Orchids of Mexico by Hagsater et all. The very first picture in the book shows a large Agave with a Laelia blooming on a branch above it! It's the only orchid book that is organized by habitat type...tropical rain forests, tropical dry forests, arid zones and scrubs, etc. It's also unique in that gives the scientific names for the succulent plants that share habitats with orchids...Neobuxbaumia multiareolata, Pachycereus pecten-aboriginum, Plumeria rubra, Pseudobombax ellipticum, Pseudosmodingium perniciosum, Stenocereus weberi, etc. Plus, there are numerous really nice habitat shots.

Mexico probably has the most species of dry forest orchids...but they can also be found throughout the Americas, Africa, India, Asia and Australia. Besides Mexico... Bolivia and Madagascar are also extremely species rich. I linked each country name to the satellite view in Google Maps. You'll notice that Bolivia and Madagascar both have a green side and a brown side while Mexico has a large brown area sandwiched in by two green sides. As I'm sure you're all aware...these 3 countries are extremely rich in succulent plants as well.

So which are the driest growing epiphytic orchids? These are the orchids that I'd put my money on...

Africa - Ansellia africana, wide distribution in Africa. It's the only epiphytic orchid not only in Botswana but in Namibia as well. Sometimes found growing on top of Baobab trees.

Americas - Oncidium cebolleta, small pseudobulbs and fleshy leaves. It has hallucinogenic properties so it's kinda like the peyote of the orchid world.

Australia - Cymbidium canaliculatum, I believe that this is the Westernmost occurring epiphytic orchid in Australia.

Madagascar - Hard to say...maybe Angraecum decaryanum or Aerangis decaryana. If you like plants from Madagascar, then I'd highly recommend the Field Guide to the Orchids of Madagascar by Phillip Cribb and Johan Hermans. Each entry has a distribution map and habitat description.

Here's a photo of Oncidium cebolleta and Cymbidium canaliculatum in the Huntington Desert Conservatory...

Oncidium cebolleta and Cymbidium canaliculatum by epiphyte78, on Flickr

Culture wise, all CAM epiphytic orchids are from summer rainfall areas so you probably want to grow them with your summer rainfall succulents. That being said, all my orchids received 30 inches of rain this past winter and were perfectly fine. They are all mounted though so they have perfect drainage.

If you attach your CAM orchids to branches then it's really important that you fasten them as securely as possible. I use 15 to 20lb fishing line and tie a slip knot on one end so I can tightly cinch the fishing line around the orchid and branch without losing tension. With rain forest orchids it's ok to place a little moss between the orchid and the mount but with dry forest CAM orchids I wouldn't recommend using any moss.

If you grow them in pots, it's safer to go with inorganic media. Large bark works fine as long as it is replaced as soon as it starts breaking down. Once it starts breaking down then the orchid can be very susceptible to rot. The Santa Barbara Orchid estate grows many of their orchids in 3/4" gravel and they water 1 to 2 times a week during summer.

Here in Glendale I water most of my orchids 2 to 3 times a week at night during summer. My backyard is tropical but my front yard is all drought tolerant plants...

Front Yard by epiphyte78, on Flickr

When the trees and shrubs get larger I plan on moving more of my CAM orchids to the front yard in order to see which ones adapt the best to my once a week summer watering schedule.

Part of the fun of succulents is the very wide range of variety and diversity...there's always a new group of plants to learn about and try. That's the same reason I like orchids! If you're looking to expand your horizons I highly encourage you to consider the epiphytic CAM orchids from dry forests.

Speaking of diversity...epiphytes are a diverse bunch as well. My very first epiphytic Rhododendrons just arrived in the mail yesterday from Bovees Nursery...and I've already attached both of them to my tree.

[epiphyte]

If anybody is interested...here's a discussion on CAM orchids in Southern California.

[Kim]

Your thread is my first introduction to this kind of metabolism. I've read before that, for example, it makes no sense to water grass at night because the stomata aren't open and the grass can't actually take in the water. ( I'm sure that's a very crude understanding.) Am I correct that your plant collection revolves around this particular phenomenon? If so, could you talk more about why these plants interest you?

As an aside, I note the significance of the species name, Cymbidium canaliculatum, which refers to the channel-shaped rib of the leaf, possibly to direct scarce water toward the center of the plant, the better to reach the roots? Is that correct, or do I misinterpret?

Thanks for posting this fascinating subject.

[epiphyte]

Kim, hmmmm...yes, I think most of my plants are CAM plants. The appeal for me is that they can grow in habitats and micro-habitats that are too dry for most other plants. Plus, as I mentioned, they are incredibly diverse.

Generally though I consider myself to be an epiphyte enthusiast. When I was in the military we frequently used the term "force multiplier". Epiphytes are "appeal multipliers". For example, a columnar cactus has "x" appeal...but when you add an orchid (or Tillandsia) to it then its appeal is multiplied...Zelenkoa onustum growing on a cactus. Here's another example...epiphytic Rhododendron growing in a Platycerium attached to a tree fern.

I've read quite a bit on the adaptations that orchids have for drier habitats...but I've never run across any references to channeled leaves directing additional rain water to the orchid's roots. It makes sense that V-shaped leaves would direct more water than flat leaves.

The thing is though...a V-shaped leaf is halfway to an O-shaped leaf. If you look at the photo of the Oncidium cebolleta and Cymbidium canaliculatum...you'll notice that the Oncidium cebolleta also has a channel...albeit much smaller. There are numerous orchid species with terete (O-shaped) leaves and generally they come from drier and/or more exposed habitats. Dendrobium canaliculatum has leaves that are more terete than canaliculate...then there's Brassavola subulifolia, Dendrobium teretifolium, Luisia teretifolia, Tetramicra canaliculata, Vanda teres...

At one point in their history these species had V-shaped leaves. Their leaves gradually folded and rounded into a terete shape. The benefit of a terete leaf is reduced surface area which helps reduce water loss. So I wouldn't be surprised if Cymbidium canaliculatum eventually had terete leaves.

You're welcome to come by for a tour some time. If you are a member of the palm society I'd say to come by after visiting Loran Whitelock's place this Saturday. My house is less than 5 minutes away but Loran's garden is an impossible act to follow!!