Today's Ramble was led by Linda Chafin.
The photos in this post, except where
noted, came from Don's Facebook album (here's the link).
Today's post was written by Dale Hoyt.
36 Ramblers met today.
Announcements: We welcomed our
guests and new ramblers: Tom, Terri and Eileen.
Today's reading: Rosemary read Each of Us Has a Name, a poem
by Zelda.
Show and Tell: Richard brought
a leaf from an Asian Cherry tree.
Today's route: We first went to the
Gardenside Room in the Conservatory to look at the Southern Flame Azalea exhibit/show.
From there we went into the International Gardens, moving through Spanish
America and American South sections, the China and Asia section, the Pitcher
Plant Mountain Bog, the Native America/Southeastern Tribes sections then out
into the Herb and Physic Garden; then back into the Visitor Center for
refreshments and conversation at the Cafe Botanica.
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| Extrafloral Nectaries on the petiole of an Asian Cherry tree. |
Extrafloral nectaries (EFNs): A large
number of plants have EFNs and they may be found on many different plant parts,
not just the petiole. As the name implies, they are found almost anywhere but
the flower itself. Which raises the question: why bother to produce nectar at
places other than the flower?
The most likely answer was seen when we saw the Peonies. Their unopened buds were
swarming with ants. The ants are here for the nectar which is produced by
inconspicuous patches on the edges of the floral bracts that protect the bud. The
near invisibility of the peony EFNs led people to propose that the ants helped
the flower buds open. You can still find this explanation on many internet
sites. Although peonies have not been studied, a variety of other EFN bearing
species show less damage to their leaves and fruits when ants are present. If ants
are prevented from accessing the EFNs, or the EFNs are removed, herbivore damage
increases. Thus the ants act as bodyguards, chasing away or eating potential
herbivores. It's like the benefit of locating a store next to a donut shop –
the presence of police eating donuts decreases the incidence of criminal
activities in nearby stores. This post by Kathy Keeler,
an early researcher on EFNs has a clear discussion with numerous examples of
EFNs. You can also see how many plants have EFNs by reading this abstract from
one of her papers.
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| Ants on Peony bud. |
Our Black Cherry, like the Asian
Cherry, has EFNs on its leaf petiole. Black Cherry leaves emerge early in the
spring at about the same time as Tent Caterpillars hatch from their eggs. When
the ants are present damage to the cherry leaves is reduced. The ants can kill
the small, just hatched, caterpillars.
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| A large yucca from Mexico. |
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| A closer look at the yucca inflorescence. |
The large Yucca sp. towering over us is from Mexico. Yuccas have their
greatest center of diversity in the arid southwest. All the yucca species also have
a mutualistic relationship with a group of tiny moths. These moths are the only
pollinators of the yucca flowers and their caterpillars eat only yucca seeds.
It works this way: The stigma of the yucca pistil (the female part of the
flower) is not exposed as it is in typical flowers. Instead, the stigma is
located in a recess at the end of the pistil. This prevents pollen carried by
bees or other pollinators from landing on it. The only effective pollinator is
the yucca moth. The female moth has a specialized mouth part that is used to
collect yucca pollen, compacting it into a tiny ball. When a pollen bearing
yucca moth enters another flower it climbs to the top of the pistil and, using
its specialized mouthpart, tamps the pollen ball into the recess where the
stigma is located. The pollen germinates and the pollen tubes grow through the
pistil into the ovary where they fertilize the waiting ovules. Once fertilized
the ovules begin to develop into seeds.
After pollinating the flower the female
crawls to the opposite end of the pistil, the ovary, and inserts several eggs
into the ovary wall. When the eggs hatch the caterpillar crawls into the ovary chamber
where the developing seeds are growing and begins to devour seeds. These seeds
are developing because the caterpillars parent pollinated the flower. The yucca
can only produce seeds if the yucca moth pollinates it and the yucca moth can
only produce young if there are yucca seeds for it to eat. So what happens if
the caterpillars eat all the seeds? When there are too many seeds being eaten
the plant somehow senses that and aborts that flower. The only flowers that
survive have a small number of caterpillars, small enough to guarantee that
some seeds will survive.
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| Yellow pitcher plants in bloom. |
Several pitcher plants are blooming in the bog garden. These plants have
highly modified leaves that form the "pitcher." They grow in boggy
conditions in nutrient-poor soils that are low in nitrogen compounds. The
function of the pitcher is to provide the nitrogen that is missing in their
diet. The pitcher fills with water (when it rains) and insects that alight on the
waxy rims of the pitcher slip and fall into the water. Some attempt to climb
back out, but the pitcher often has downward pointing hairs that prevents them
from doing so. Eventually the bugs drown and begin to decay. The result is a
stinky broth of rotting insect, bacteria and nitrogenous compounds that supply
the nutrients missing in the soil. The pitcher absorbs the compounds needed for
the plant to grow.
Pitcher plants have flowers that are
equally bizarre. They hang upside down and the petals are long and drooping.
The end of the pistil is greatly expanded to form a shelf, somewhat like an
upside down umbrella, spreading to fill the space surrounded by the petals. The
anthers are located above the this shelf, so as they shed pollen it falls into
the expanded pistil end. Bees can easily enter the flower only between the
hanging petals. When they do they pick up pollen on their bellies as they crawl
around on the shelf. That pollen is transferred to the next flower they visit
when they crawl between the petals. The stigmatic surface of the pistil is at
the edge of the "umbrella" right in the gaps between the petals.
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| Flower of yellow pitcher plant; the pistil is not fully open yet. |
You can get a closer look at this
unusual flower if you look at the pitcher plants growing in the pool at the
visitor center.
SUMMARY OF OBSERVED SPECIES:
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Florida Anise
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Illicium floridanum
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Yucca, Mexican species
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Yucca sp.
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Unidentified species of oak
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Quercus sp.
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Agave
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Agave sp.
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Green-and-Gold
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Chrysogonum virginianum
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Cherokee Sedge
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Carex cherokeensis
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Mariana Maiden Fern
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Macrothelypteris torresiana
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Woodland Phlox
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Phlox divaricata
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Eastern Bluestar
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Amsonia taberaemontana
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White Wild Baptisia
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Baptisia alba
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Wild Pink
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Silene caroliniana
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Lily of the Valley
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Convallaria sp.
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Silverbells
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Halesia sp.
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Southern Flame Azalea
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Rhododendron austrinum
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Big Leaf Magnolia
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Magnolia macrophylla
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Pansies
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Viola sp.
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Asian Solomon's Seal
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Polygonatum odoratum
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Peony
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Paeonia sp.
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Alabama Snow Wreath
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Neviusia alabamensis
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Virginia Springbeauty
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Claytonia virginica
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Oconee Azalea
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Rhododendron speciosum
(=Rhododendron flammeum)
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Plum Azalea
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Rhododendron prunifolium
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Yellow Pitcher Plant
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Sarracenia flava
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Georgia Rockcress
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Arabis georgiana
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