Field of Science

Flushed with success

Regular visits to our teaching greenhouse are part of my job and mental health program. Although the facility is not physically impressive, the number and variety of plants contained therein is quite impressive. Interesting observations of exotic plants happen regularly.

Over 20 years ago I brought a small tropical tree seedling back from Queensland Australia. It’s the genus Maniltoa in the legume (bean) family and it now has nearly outgrown the greenhouse. If it were not pushing up against the greenhouse glass this tree’s limbs and leaves would show a graceful arching. But this plant has a most unusual and ornamental feature. It produces huge buds from which emerge whole branches bearing nearly full-sized leaves, but here’s the strange part, these branches and their leaves are pink and totally limp. They dangle down like rags, and since the tree tends to flush, a number of such pink branches emerge from buds all at once. Such flushes of new vegetation are thought to overwhelm herbivores that might attack the new foliage.

Slowly, over a couple of weeks, the pink pigments fade and chlorophyll slowly develops turning the leaves pale green. And then, over another few weeks, the branches and leaves slowly pull themselves up into a rather graceful arch. They accomplish this by having a specialized swollen zone called a pulvinus at the base of leaflets, leaves, and branches. Looking and acting a bit like a knuckle, the pulvinus (see close up on right) reorients the branches and leaves. The same structures close up and droop many legume leaves at night and account for the movement of leaves on the touch sensitive Mimosa pucida, another legume.

So our Maniltoa has provided us with a bit of colorful tropical cheer on a cold, late winter day. Enjoy.

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