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Re: secondary hemiepiphytes

In response to Alan's questions: Plants have adapted to epiphytism primarily
to get up in the canopy where there is more light, less competition from
other plants, increased pollinator activity and possibly for protection from
ground herbivores. The tropical forest floor is extremely dark except in
forest gaps. Plants that have developed either hemi or true epiphyte strategy
are often rewarded with greater or more efficient pollinator activity, more
light, better seed dispersal, additional nutrient from cloud and other
advantages. Many of these hemiepiphytes are from high rainfall areas that are
wet rather constantly year round, so they can get a lot of water either on
the ground or up, so electing to stay at ground level provides few if any

True epiphytes have a different root structure that allows them to very
efficiently absorb and hold even trace amounts of moisture very quickly. They
can grab moisture and nutrients from the rainforest clouds as they pass
through the canopy. Other epiphyes in the canopy, such as the bryophytes,
release nutrient into the cloud water as the cloud passes through, and plants
nearby can absorb this nutrient readily as the nutrient saturated cloud
passes over them. The cloud also picks up nutrients from other plant matter
in the canopy and transfers it to other areas, sometimes far away. There have
been a number of studies about canopy nutrient cycling in recent years that
describe this process. All of this activity serves to provide suffient levels
of nutrient to epiphyte colonies that sometimes attain massive ecosystems
high above the forest floor. Hemiepipytes want to get up there to tap into
this richness and to join the party!

Hemiepiphytes may also develop other similar root strategies as found in
epiphytes once they leave the ground behind. Leaves, stems and roots of some
species in seasonally dry areas may develop to become very succulent for
storing water. Some of the bird's nest type anthurium may trap debris that
helps to hold moisture and provide extra nutrient. The canopy life is not so
easy however, and can be harsh, much hotter than on the ground. Even in the
rainest areas of the world, epiphytes must endure brief scorching dry periods
more intense than anything encountered on the canopy floor.

Many climbing and/or hemiepiphytic aroids will not flower unless they can
scramble to great heights. Hemiephytes have developed flowering strategies to
utilize different pollinators or seed dispersers that reside high in the
canopy. These agents are perhaps not found on the ground, or the canopy
residents may be more efficient at their tasks than ground dwellers, so the
hemiepiphtye wants to get their flowers up to them. Whatever the case, there
may be a number of compelling reasons why a plant might evolve into a
hemiepiphte rather than stay on the ground where there it can survive more
easily with a steady water supply. Major driving forces for change are those
that promote success in pollination and seed dispersal.

Donna Atwood
Selby Gardens

 (1) I'm wondering whether anyone has any other examples of this in the
 aroid family.

 (2) Is there any evidence or explanation as to why any plant would elect
 to dispense with a ready supply of water by doing this? Is there some
 energy consideration involved (eg., too expensive to maintain
 connections to the ground)?

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