A close look at some orchids will reveal two types of
roots: those growing on the substrate and those that
form a “basket,” up and away from the plant. Basket roots
aid in trapping leaf litter and other organic material that,
when decomposed, can be used as a mineral source by
the plant. Orchid flowers are among the most beautiful
in the plant world (plates 3- 51– 52). Some, like the
familiar Cattleya, are large, while others are delicate and
tiny. Binoculars help the would- be orchid observer in
the rain forest. Orchids are cross- pollinated by insects;
certain orchids can be pollinated only by specific insects.
Bees are primary pollinators of Neotropical orchids.
These include long- distance fliers, like the euglossine
bees, which cross- pollinate orchids separated by
substantial distances. Some orchid blossoms apparently
mimic insects, facilitating visitation by insects intending
(mistakenly) to copulate with the blossom— something
that Charles Darwin discovered. Many orchids have
value as ornamentals. Of particular significance to
humans is the orchid genus Vanilla, which contains 90
species, two of which are of economic importance, their
use dating back to the Aztec.
Epiphylls
In many tropical moist forests, even leaves have
epiphytes. Tropical leaves often are colonized by tiny
lichens, mosses, and liverworts, which grow only after
the leaf has been colonized by a diverse community
of microbes: bacteria, fungi, algae, and various yeasts,
as well as microbial animals such as slime molds,
amoebas, and ciliates (plate 3- 53). This tiny assemblage
that lives upon leaves is termed the epiphyll community.
Its existence adds yet another dimension to the vast
species richness of tropical moist forests.
The Understory and Forest Gaps
Much of the understory of a closed tropical forest is
deprived of light (plate 3- 54). Low light intensity is a
characteristic feature of rain forest interior and is an
important potential limiting factor for plant growth.
This is the reason it is fairly easy to traverse your way
through a closed- canopy rain forest. Many of the
seedlings and shoots that surround you are those of
trees that may or may not eventually attain full canopy
status; a small, unpretentious- looking sapling could be
well over 20 years old.
Plate 3- 53. Epiphylls of various kinds adorn this large leaf in
the forest understory. Photo by Scott Shumway.Plate 3- 54. Light areas called sun flecks penetrate the
otherwise dark interior of a closed- canopy rain forest.
Photo by John Kricher.Plate 3- 55. Forest gaps allow much light, stimulating rapid
growth. Photo by John Kricher.56 chapter 3 rain forest: the realm of the plants