Palo verde

I posted in April about the sunbursts of palo verde trees (foothills PV: Cercidium microphyllum, syn. Parkinsonia microphylla, and blue PV: Cercidium floridum, syn. Parkinsonia florida) in full flower. These unique trees have green bark that photosynthesizes like leaves! Well, maybe not quite like leaves – I need to find out more about how they exchange carbon dioxide with the surrounding air. I bet the cells have a slightly different structure. Anyone reading this know?

These palo verde seedlings appear almost to glow in low light conditions like a rainstorm. I need to take my waterproof camera out with me soon to capture that!

Anyway, their seedlings germinated in force throughout the Tucson mountains last week, after a 4th of July celebratory rainstorm. These trees produce seed pods much like snow peas you grow in your garden, which is hardly surprising, given that they are in the pea family, and which are edible and taste like peas, but nuttier. Tiny beetles lay their eggs in many seed pods, then hatch out and eat the seeds. They may claim a quarter to a half of the seed crop, according to the seeds I collected and observed beetles hatching from (several thousand seeds from three sites).

The seeds that survive the beetle onslaught are often in pods with siblings, so groups of up to five of these enormous, luminous, hilarious looking seedlings have been germinating in hollows throughout the volcanic slopes of the Tucson foothills. Consider five small seedlings in a space smaller than one tree. Only one can survive long enough to reproduce, clearly. So does this hedge the tree’s bets, or reduce the vitality of all the seedlings? Do trees that produce seeds in pods of 1-2 seeds do better than those dropping pods of four seeds at a time? These would be some interesting questions to investigate.

I have noticed a number of them disappearing, but not as many as I might imagine if the plentiful desert cottontails or ground squirrels were eating the juicy-looking cotyledons. I have game cameras deployed in the foothills, and I am wondering: where do these seedlings go?

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