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The Understory
RAINFOREST SHRUBS
July 22, 2007
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Like hardwood tree saplings, ground-dwelling rainforest plants and shrubs have adapted to life in the low light levels of the forest floor. They often have structures very similar to those of saplings: dark undersides, deeper colored leaves, and large leaves. Even so, because of the shaded conditions, a true shrub story is unusual in forests and only scattered vines and shrubs are present. Many of the herbaceous plants of the rainforest are epiphytes, including ferns, bromeliads, orchids, and arums, although there are also exclusively terrestrial plants like some of those of the Zingiberales Order including heliconia, gingers, bananas, and birds of paradise. These plants are known for their colorful bracts and are also found in light gaps and under secondary growth conditions.
The world's largest flower, from the rafflesia epiphyte, is found on the rainforest floor. The largest recorded specimen had a diameter of 45 inches (1.14 m), but the average diameter is around 30 inches (75 cm). The plant exists most of its life as vine root, and only becomes visible when it emerges as cabbage-like structure. From this ugly structure comes the maroon and yellow flower which blooms for 3-4 days before dying. The flower releases a putrid smell which attracts flies for pollination. Rafflesia seeds are thought to be dispersed when large mammals like pigs tread on them and carry the seeds away, stuck to their feet. The loss of large mammals may be hindering rafflesia populations.
Another noteworthy group of forest-floor plants from Southeast Asia are the monkey cups. These plants, like the pitcher plants of other parts of the world, have modified leaves for catching insects, which serve as a source of supplementary nutrients like nitrogen and carbon. Interestingly, pitcher plants raised with good soil conditions produce few, if any, pitchers.
Near light gaps and forest edges where sunlight is stronger, big-leaved plants like heliconia (bananas) are more common. Heliconia are famous in the New World for their large colorful flower-like bracts. These bright red, orange, and yellow structures house flowers that produce copious amounts of nectar which attract hummingbirds and insects. Hummingbirds like to visit more than one species of heliconia, creating a risk of hybridization, so different species of heliconia have flowering parts of different lengths allowing the heliconia to deposit its pollen on a specific part of the bird. When the hummingbird visits another heliconia of the same species, the flower has receptor parts that catch the pollen off the particular part of the bird.
Forest floor in Borneo. Click image for more information. (Photo by R. Butler)