Crassulacean Miracles

Some of my CAM plants: back, Agave colorata, A. americana Medio-Picta; middle, Hechtia 'Texas Red' w/ Sedum 'Anglina', Agave gentryi 'Jaws', Puya venusta, Aloe (?); front, Puya chiliense, Dyckia 'Big Red', Senecio mandraliscae and Agave parryi 'Cream Sickle'

Some of my CAM plants: back, Agave colorata, A. americana Medio-Picta; middle, Hechtia texensis’ Big Red’ w/ Sedum ‘Angelina’, Agave gentryi ‘Jaws’, Puya venusta, Aloe (?); front, Puya chiliensis, Dyckia ‘Red Devil’, Senecio mandraliscae and Agave parryi ‘Cream Spike’

Plants for me are little windows into the working of the world. Beautiful, exotic, grand or seemingly simplistic, perfectly attuned to their place. We are simple animals ourselves our attentions grabbed and later lost by what shimmers and glitters in our minds for a moment. We look, but only partially see. Each plant is an opportunity, maybe a lesson and later forgotten by most of us, unaware that there is anything there to learn beyond our initial attraction to the physical plant itself. The unrolling of a leaf of Liriodendron, like a flag, happening 10 thousand times on one tree, each year across the span of its years, for generations for millions of years. The perfectly memorized pattern of the single enormous leaf of an Amorphophallus as it stretches up out of its corm, fully formed, each leaflet revealed as a piece, entire, not expanding through a growing tip, adding tissue, but revealing itself wholly if we watch. Each plant a miracle to all but the blind.

I was reading an article on UBC’s botany photo of the day site, on Crassula ovata (Jade Plant). It is one of the most common of the Crassula species in South Africa growing on sandy loam soils, with around 12”-18” of rain as part of what some call the ‘Albany Thicket’.


“Like most Crassula species, Crassula ovata reduces water loss from its leaves by utilizing Crassulacean Acid Metabolism, or CAM. Part of the CAM biological process is that stomata are closed during the day to prevent water from evaporating, and instead opened at night to collect carbon dioxide (this is the reverse of how most plant species exchange gases, with stomata open during the day instead). The carbon dioxide is stored overnight in the form of crassulacean acids, which are then broken down during the day. This releases the CO2 for the photosynthesis process during the day. During extremely dry periods, Crassula species may undergo CAM-idling, where stomata are not opened during the day or night. Instead, the plants will recycle the CO2 within the cells. This leaves them unable to grow or develop new tissue, but the plants are able to survive the lack of water by losing very little of it during this time.”


I’ve been largely ignorant of CAM. It’s a particularly elegant solution to the problem of aridity. It is estimated that some 16,000 species, 7% of all plants, from 300 genera and 40 families use the CAM process, exclusively or in part. Most of these are xeric plants coming from arid climates. Included, as you might expect is almost all of the family Crassulaceae including Sedum, Cactaceae, Agavaceae including Agave, Hesperaloe and Yucca; and 91% of Bromeliaceae including 24% of Puya and all Dyckia and related species. Obviously this includes a lot of other plants, many epiphytes, some quite surprising, especially those aquatic plants that take on carbon at night because there isn’t enough dissolved in the water during daylight hours. Plants taking up CO2 through conventional process can loose up to 97% of their water through evapotranspiration so this strategy provides CAM plants a way to conserve a very limited commodity.

When we choose to grow CAM plants here in the maritime Pacific Northwest, in our rich heavy soils, we shouldn’t be surprised if we lose them when we don’t make provision for their requirements. These plants evolved with aridity and a dry summer can’t make up completely for our other three seasons. If we modify the soil enough so that drainage carries moisture away from the roots we still need to remain cognizant of its other needs.  Winter may still be too wet and we’ll need to provide the shelter of an eve overhang or move the pot under roof, and we still need to be careful with summer irrigation. Their modified internal biochemistry shows us just how much their environments have pushed them. We need to go out of our way to accommodate them because no matter what we do our climate may be cooler and wetter, our soils richer.

These plants evolved in harsh environments. Rich soils with good amounts of available moisture, will push them into exuberant growth, if it doesn’t rot them, with floppy weak steams and soft growth. Gardeners need to demonstrate patience and restraint. You cannot deny physiology and internal systems. Plants cannot thrive or perhaps even survive if growing conditions are too far outside those they evolved with.   What we might think are better growing conditions can be fatal to CAM plants. Plants cannot switch their internal processes, they have been genetically hardwired into doing what they do. The fact that other plants can respond positively to available moisture and nutrients probably means that under arid conditions, they will flag and decline unable to control their massive losses of moisture during their active growth phase. Plants can only do what they can. It is part of their miracle…part of their wonder to gardeners who keep their eyes open.

Observation and science don’t explain it away, they illuminate it.


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