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Winter Hummingbird Expedition to Costa Rica
in November/December 2005 or February 2006

PINXTER-FLOWERS REVISITED

Back in the early 1970s before we thought watching birds was a worthwhile pastime, we wandered the Piedmont woods without binoculars. Instead we carried an inexpensive Sears 35mm SLR camera, a trio of screw-in close-up filters, and a hand-me-down tripod whose legs opened all the way and allowed us to get flat on the ground to photograph our favorite natural history objects: Wildflowers of the eastern U.S. In those days before digital cameras and Photoshop manipulations we used relatively expensive color slide film and were a bit more judicious about how many exposures we took, so we often waited hours for the wind to die down or the light to be just right to capture our botanical subjects. Alas, many of our favorite spots for photographing wildflowers are long gone. Where Silky Leather-flower once grew there now stands a bowling alley, and a former haven for Wild Irises was paved over as I-77 snaked its way southward from Charlotte. One of our fondest wildflower encounters came in the Saluda River bottomland near Columbia in 1970 before Riverbanks Zoo was built. There we saw our first wild azaleas--so called "Pinxter-flowers"--and marveled at their intricate structure and delicate colors. Fortunately, planners retained much of the natural area around the zoo, so it's still possible to see that same azalea colony, growing not far from where exotic Koalas now delight zoo visitors. We don't have to drive 80 miles to Columbia to see Pinxter-flowers, however, since these colorful shrubs bloom right here at Hilton Pond Center. Although we wrote once before about wild azaleas, we wanted to revisit our marvelous Pinxter-flowers to see what else we could learn.

All text & photos © Hilton Pond Center

There are several species of wild azaleas in the Carolinas, and some look quite similar. The one at Riverbanks and here at Hilton Pond Center is Pinxter-flower--Rhododendron periclymenoides (formerly R. nudiflorum)--a woody shrub that grows best in sunny, open woods with moist, rich soil of the Piedmont Region. Its flowers vary from near-white to bright pink, but the center of each blossom is always a deep rose color, with pigment on the petals AND the bases of the fuzzy reproductive parts (above). Many Pinxter-flower shrubs are in full bloom before any of their leaves appear, but around Hilton Pond the flower and leaf buds open at about the same time. In spring Pinxter-flower's deciduous leaves are a delicate yellow-green and are arranged almost whorl-like near the tips of thin twigs.

We readily admit that the delicate hues of Pinxter-flower are pleasing to view, but what fascinates us most about this native plant is the shape and structure of its flowers. There's no question that a Pinxter-flower blossom means business, and the business happens to be cross-pollination. Nectar in the pink blooms is a magnet for butterflies and early migrant Ruby-throated Hummingbirds, so it's likely that large insects and hummers alike serve as principal pollinators.

Like their leaves, the Pinxter-flowers themselves are whorled loosely at the end of a twig, in clusters of up to 12 or so (above). Each flower has five delicate petals so thin that sunlight easily passes through, creating interesting backlit effects. But to us the most astounding aspect of wild azaleas is the conspicuous assemblage of reproductive structures: A single and very long purple-tipped pistil (the female part) and five somewhat shorter male stamens (below right). The pistil's bulbous tip--called a "stigma"--is somewhat sticky and is a repository for the granular pollen grains produced by "anthers" at the end of each stamen. When a pollen grain contacts the stigma, it sends a pollen tube down the long thin style of the pistil and eventually contacts the ovary at its base; this is where fertilization actually occurs and where the embro becomes a seed. Again, that the Pinxter-flower's reproductive structures are so big leaves little doubt the blossom is NOT self-pollinating, and that the pollinator itself must be relatively large. This size criterion is met by nectar-seeking hummingbirds and butterflies, either of which would invariably bump into at least one stamen, picking up pollen that would be transferred to the next flower's pistil.

The blossoms and reproductive parts of the Pinxter-flower are indeed big and showy, and they're easily seen even from several yards away in the springtime woods around Hilton Pond. However, when we moved in on our flowering shrub to take macrophotographs, we were reminded that often it's not possible to understand the web of nature without taking a closer view. As we framed a Pinxter-flower in the camera's viewfinder, we noticed one of its stamens seemed malformed so--preferring not to photograph a "defective" flower--we swiveled our tripod head slightly to bring a different blossom into focus. We took a few exposures of the new flower and then for some reason--either curiosity, premonition, or dumb luck--felt an urge to re-examine the one with the faulty stamen. It was then we discovered the flower wasn't defective after all, but that a tiny half-inch caterpillar was nibbling away on pollen grains on the very tip of the anther (above left).

By eating pollen this almost-overlooked larva was subverting the role of the stamen, although we doubt just one miniscule caterpillar has debilitating impact. We watched the larva for nearly half an hour as it munched slowly and moved occasionally. Most of the time it held tightly to its perch with posterior pairs of "prolegs"--false legs that are appendages of the abdomen--but occasionally the caterpillar released the grip of its six front walking legs and arched upward, anchored all the while by prolegs. Eventually, the creature regained its foreleg grip and moved along the stamen inchworm-style--a behavior that leads us to believe the caterpillar was produced by a member of the Geometridae (Inchworm Moth Family), whose larvae have only two pairs of prolegs; what little we know about moth taxonomy leads us to suspect it is a species of Nemoria. Incidentally, we detected a few strands of silk the caterpillar produced, undoubtedly as a sort of safety net as it crossed from one stamen to the next.

So once again in the spring of 2005 we observed Pinxter-flowers around Hilton Pond and, as typically occurs, we found things new and marvelous. We had never really noticed that the pistil's long, thin style and the five stamen filaments are covered by tiny hairs that point toward their bases, or that in top view (above) the flower cluster radiates like spokes of a wheel. And we certainly hadn't ever seen a pollen-eating caterpillar so small that at first it simply seemed to be a deformed anther. On top of all this we think you'll agree our Pinxter-flowers at Hilton Pond Center are aesthetically pleasing, and that because there's ever more to learn about them they're always worth revisiting.

All text & photos © Hilton Pond Center

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