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NATURE HAPPENINGS - May 2008

The Moonbeam Garden
by Damian Fagan

May is the month of the Moonbeam Garden. These plants neither wither in the daylight nor live as saprophytes – living off the benefit of others. They need the process of photosynthesis to obtain nourishment and that process requires a sunlight trigger. No, the plants of the moonbeam garden are different in one aspect - their floral allegiance is to the night, the darkness, and the moon.

Some wildflowers close their flowers before darkness. Globemallows close their circular flowers for the night, often enveloping a small diadaysia bee within their embrace. Sort of like a flowery B&B – bees and bloom. In the morning, the flower opens like an umbrella and the bee flies off. But flowers in the moonbeam garden do just the opposite, they unfurl their petals as darkness approaches and close up shop with the morning’s light.

Two close moonbeam garden relatives are the pale evening primrose (O. pallida) and the dwarf evening primrose (Oenothera caespitosa). Whereas the pale one is taller and bears white flowers about 1 ½” wide, the dwarf species grows low to the ground and has much larger flowers. Some naturalists call these “Kleenex flowers,” for when prolific blooms cover the desert it resembles tissues wildly scattered from a box. And like other night-blooming plants, the primroses have developed a different pollination strategy.

In the early evening, primrose flowers begin to open. Slowly, the process takes about 45 minutes for a dwarf evening primrose flower to open, but it is a petalous performance worth watching. As the white buds “burst” out from the confines of their protective sepals, they twist to open, moving at a snail’s pace. When open, the flowers are ready for pollinators and they release a sweet aroma to lure night flying insects such as white-lined sphinx moths.

Sphinx moths are large moths. Nicknamed “hummingbird moths” because of their heavy bodies and buzzing flight, these moths fly low to the ground in search of blooms. When a flower is found, the moths hover in front of it and uncurl their long proboscis, which goes deep into the flower’s tube. As they lap up nectar, the moths gently bump their heads against the flower’s stamens or pick up some pollen on their proboscis. Dusted with pollen, the moths move on to the next flower and, according to design, some of the pollen gets transferred to the new flower’s stigma. Pollination complete. If all goes well, the flowers respond by turning a pinkish hue, a signal to the pollinators that they are no longer producing nectar and have been pollinated.

Though the moths are not host-specific, a female sphinx moth may lay some of her eggs on the leaves of the primrose. These leaves provide host food for the developing larvae. The greenish caterpillars resemble your garden’s tomato hornworms, for they are close relatives of the sphinx moth.

Besides the primrose, there is the snowball or sand verbena (Abronia fragrans) with its cluster of tubular white flowers that form a snowball shape when all the flowers open. The verbena attracts sphinx moths in a similar fashion, with sweet aroma and nectar rewards, but sometimes an early morning butterfly may feed on the flower’s nectar prior to closing time.

One classic genus of plants in this garden is the Yuccas. Members of the Agave Family, their flowers open in at night and attract a particular species of moth, called the yucca or pronuba moth. The female of this species gathers a small ball of pollen in her mouth and pollinates a receptive yucca plant, then deposits her eggs in the base of the yucca’s ovary. As the fruit develops, the larvae feed upon the maturing seeds. These small ½” long moths are easy to view at night as they crawl over and into the yucca’s bell-shaped flowers.

Other members of the moonbeam garden include sacred datura, Indian tobacco, phlox, four o’clocks, and blazing stars. So on your next camping trip, spend some time watching for these nighttime bloomers and their pollinators; they are as fascinating as their daytime cohorts are.
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