C4 Yourself!
Euploca polyphylla (aka Heliotropium polyphyllum)
Boraginaceae, the heliotrope family
Ever wonder how some species flourish, bloom, and prosper at ground level in the hottest, most sun-parched habitats. I accidentally dropped a digital temperature-recorder in a dry marsh the other hellishly sunny day, and it maxed out flatlined at 115 degrees F before I recovered it. Who knows how much higher the actual reading should have been? Think of walking barefoot across hot asphalt on a bright hot day. That’s why there are no plants in Hell. Maybe it is counterintuitive that it often tends to be (a lot) hotter on the ground than above it. A burnin’ ring-o-fire at ground level can raise fun questions:
All photos today by John Bradford. This is how the PH looks this morning.
Do the broad lower leaves under a saw palmetto or the skirt of dead foliage under a Golden Aster heat-shield the more-delicate tops? How important is evaporative cooling on the down low? Why do some plants have rosettes during the cool season and move their leaves up the stem in the heat? Does it help dry marsh plants have a “mulch” of spongy periphyton persist from the wet season? Does leaf litter protect shallow roots? Why do sedges often cluster leaves at the top of the plant? Why do low Myrtle Oaks in scrub have a bewildering array of leaf forms, sizes, and textures? And so forth. A fun theme for a walk with one of those point and shoot “covid” no-touch thermometers.
Let’s get to the point via one final question. How do the species that actually love the hotfoot soil get away with it? Yes, some have extreme adaptations, like Cacti. Some dodge hot times or actual fire & flood using seeds, or deep roots, or shape-shifts. Harsh habitats are good opportunities for species able to tolerate them, because harshness suppresses competition, and pestilence may be tamped down too. In a “nice shaded moist” rainforest you’re competing with a zillion close neighbors. By contrast, in the desert or Florida scrub there’s plenty of real estate, if the harsh physical conditions don’t thwart you. The late British ecologist J.P. Grime divided basic plant lifestyles into a triangle: competitors, ruderals (weedy fly-by-nights), and stress-tolerators. (Hey, that’s kinda like office politics.)
This all leads to the fact that being a stress tolerator can open doors. Especially in “new” environments with changing climates, such as the passage of an ice age. A local stress tolerator is the beautiful Pineland Heliotrope. It stands up to ground-level cookery even without obvious protections.
Biologist Michael Frohlich and about 19 collaborators nailed that mystery with molecular research. Pineland Heliotrope’s secret weapon is a superpower called C4 photosynthesis, best known in grasses, which live at ground level. C4 allows comfort and joy in places too hot and dry for many competitors. What’s interesting about this ability in heliotropes is that only some have it. As the Frolich team uncovered, there’s a cluster of about 18 species (in the genus Euploca) that evolved and diversified rapidly in hot exposed American habitats thanks to an ancestor bestowing upon them the C4 ticket to invulnerability. So they prosper in the exclusive stress-tolerator corner of Grime’s triangle. How cool is that?
To dig in deeper:
https://academic.oup.com/botlinnean/article/199/2/497/6510913