Today's Ramble was led by Dale Hoyt.
All the photographs of today’s ramble, except where
otherwise credited, were taken by Ted LaMontagne; they can be seen on the SBG
Nature Rambling Facebook album.
Today's post was written by Dale Hoyt.
26 Ramblers met today.
Today's reading:
KathyLynne read a poem by Maxine Kumin:
Appetite
by Maxine Kumin
I eat these
wild red raspberries
still warm from the sun
and smelling faintly of jewelweed
in memory of my father
wild red raspberries
still warm from the sun
and smelling faintly of jewelweed
in memory of my father
tucking the napkin
under his chin and bending
over an ironstone bowl
of the bright drupelets
awash in cream
under his chin and bending
over an ironstone bowl
of the bright drupelets
awash in cream
my father
with the sigh of a man
who has seen all and been redeemed
said time after time
as he lifted his spoon
with the sigh of a man
who has seen all and been redeemed
said time after time
as he lifted his spoon
men kill for this.
Today's route:
Avoiding mosquitoes was a priority today, so we kept out of the shaded areas.
From the Visitor Center we walked down the road to the bottom of the Dunson
Native Flora Garden and then up the power line right of way to the Prairie
Restoration Plot, and then across the lawn to the road and returned to the
Visitor Center.
Show & Tell – acorns
again: At risk of being accused of beating a dead horse, I again brought in
twigs of a red oak group to show everyone the developing acorns.
Todays sample
was Southern Red Oak (Quercus falcata) and a lot of ramblers were surprised at
how skinny the leaves were. That’s because these twigs and leaves came from the
upper branches of the tree and the leaves we’re accustomed to seeing are all
from the lower, shaded branches. The difference is between sun leaves, which
are smaller and narrower and the shade leaves, which are larger and broader.
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| Southern Red Oak leaves note the long, skinny shape and the curved midvein, typical of the SRO leaf. |
The size and shape of a leaf is a compromise between
water loss and photosynthetic capability. Leaves on the upper branches are
exposed to more wind and, thus, water loss. To reduce the loss of water they
are smaller. This should reduce their photosynthetic capacity, but the sunlight
is more intense, so they are thicker and have more layers of photosynthetic
cells. The shade leaves are exposed to less light and wind, so they can be
larger, which means more surface area to capture more, less intense, light.
And, by the way, since Southern Red Oak is in the red oak
group, it takes two years for its acorns to mature. Some of the branches I
passed around had two generations of acorns:
tiny acorns developing on this year’s
growth along with larger acorns on last year’s growth.
The larger acorns would
have been dropped this fall; those on the new growth would mature in the fall
of next year (2019).
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| Southern Red Oak. New acorns developing on this year's new growth. |
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| Southern Red Oak. Larger acorns developing on last year's growth |
Peeking into the
Dunson Native Flora Garden:
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| The composite flowers of Rough Daisy Fleabane |
Walking along the road we can peek into the Dunson
Garden, taunting the mosquitoes and stopping for a few plants that capture our
attention. Our first surprise was a type of Fleabane, possibly a Rough Daisy
Fleabane (Erigeron strigosus). (The
photograph is from an old ramble.)
What appears to be a flower with a yellow center and
white petals is, in reality, composed of many tiny flowers of two types: ray
flowers and disk flowers. Each ray floret (the word for a tiny flower) has a
single, strap-like petal. Each disk floret is yellow in color. Together they
form a flower head composed of many little flowers: a composite flower. You’ll be familiar with other types of composites
like asters, daisies, sunflowers and coneflowers, all members of the Aster family,
Asteraceae.
How the tiny florets are arranged to appear as a single,
larger flower is not so obvious. Imagine an empty garden with a single furrow
ready to be planted. Only this row isn’t straight; it’s a spiral, like the
groove on an old-fashioned vinyl record. Start at the beginning of the spiral furrow,
on the outermost edge. Now plant a tiny floret with a single white petal,
making sure that the petal points away from the center of the spiral. Walk around
the spiral, planting these white petaled florets at short intervals, until you
come to the point nearest where you started. Continue walking along the spiral
but now start planting little yellow florets that don’t have the large petal.
Keep walking and planting until you reach the center of the spiral. You have
just made a composite flower head!
Of course, real world flowers aren’t flat like a vinyl record.
To make your composite flower more lifelike you’ll have to imagine that your
spiral is centered on a circular hill. If the hill is just a gentle slope,
you’d have a daisy with its yellow center raised a bit above the edge of the white-petaled
florets. If it’s a steep hill you’d have a cone flower, a single row of ray
florets around the base and all the disk florets winding around to the top. (To
make a cone flower you’d also have to plant different colored ray and disk
florets.)
This analogy isn’t too far off from how real composite
flowers develop. Except that that instead of starting from the outside, the
florets are “planted” from the center, at the top of the hill. And there is no
hill, yet. At the point where the center of hill will be there is a clump of
cells called the floral meristem. This special tissue gives rise to all the
embryonic florets. At the same time, it creates the “hill” in which the
embryonic flowers are imbedded. The first floret primordium produced will
develop into the first ray flower. The second will appear roughly 137 degrees
away from the first, as will each subsequent floret primordium. As the
embryonic florets are formed they are pushed away from the floral meristem,
along with other embryonic tissues that become part of the flower head. This
results in a spiral pattern of florets that is apparent when you look at the
disk of a sunflower.
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| Sunflower, a composite with a large number of disk florets and many yellow ray florets. (photo By 3268zauber [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Common) |
Another thing to notice about the composite flower head
is the flowering pattern. The first primordial florets are on the outer part of
the spiral. They are the ray florets. As you move inwards on the spiral you encounter
younger and younger florets. Because the older florets will bloom first you
will see a wave of development in the flower head. Look at the disk florets in the
photo of the sunflower head: the outer, darker ring is composed of disk florets
that are blooming. The florets in the center are immature and not yet open.
Bees will spend all their time visiting the florets in the outer ring.
Another common pattern in composites like sunflowers is
that the ray florets are sterile. It’s as if they put all their energy into
making a big petal and don’t have enough left to make stamens or pistils.
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| Florida Torreya |
One of the trees visible from the road is a Florida torreya, or Stinking Cedar (Torreya taxifolia), a federally
endangered plant, formerly found in the ravines of the Chattahoochee and Flint
rivers in Georgia, but now restricted to ravines of the Apalachicola (the Floridian
name for the Chattahoochee) in the Florida panhandle. The tree is endangered not
only because of its restricted distribution, but also because it has been attacked
by a fatal fungal pathogen. The Florida population is slowly declining as the
infected tree fail to reproduce and die. Many Botanical Gardens, including
ours, are participating in a rescue operation by planting cuttings in their
gardens. Research is continuing to find a cure, with the hope that it is found
before the Florida population becomes extinct. The specimen in the Dunson
Garden was planted in 1980s.
One of the common names is a misnomer. Torreya is not a cedar,
it is in the Yew family.
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| The enormous, doubly compound leaf of Devil's Walking Stick |
Another unusual plant growing near the fence is Devil’s Walking Stick, Aralia
spinosa. Not only is the stem covered with spines, this plant has the
largest leaf of any plant native to North America. Some of you may be shaking
your head about this because you know that Bigleaf Magnolia has a leaf that
considered to be pretty big. True, but the Bigleaf Magnolia has the largest simple
leaf. The Aralia leaf is a compound leaf. In fact, it is doubly compound, with leaves that can be as long as 4 feet. It is
hard to grasp a leaf that size, but not nearly as hard as to grasp the trunk.
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| American Euonymous (Hearts-a-Bustin') flowers displayed against the leaves. |
Hearts-a-Bustin',
American Euonymous (Euonymous americana),
continues to bloom. Many of the leaves visible through the deer fence had
several flowers, apparently growing on their surface. This is not the case,
however. The flower stalks arise from the leaf axil and grow along the surface
of the leaf, so when the flowers bloom they are set off by the glossy green
leaf background.
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| Black Cohosh infloresences lighting up the shadows |
Black Cohosh (Actea racemosea) has begun to bloom and
the single plant visible from the road looked like a candle in a gloomy room.
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| Flower bud of Purple Passion Flower |
Two weeks ago the Purple Passion
flower vines (Passiflora incarnata)
were less than a foot tall. Now many are climbing up the deer fence to a height
of more than six feet. There are even a few vines with flower buds. Their rapid
climb up the fence is accomplished with tendrils: long, thread-like appendages
that emerge from each leaf node.
Each tendril appears motionless, but with time-lapse photography,
it will be seen to move in a circular pattern. This movement goes by the lovely
name of circumnutation. Charles
Darwin discovered this pattern of plant movement by placing a sheet of glass
above a plant and marking on the glass the position of the plant’s tip over the
course of many hours. He found it moved in a circular pattern and published the
results in 1875 in On the Movements and
Habits of Climbing Plants.
It appears as if the tendril is searching for something.
When it does come in contact with something the end begins to coil about
whatever it has touched, and, the remainder of the tendril also begins to coil.
This shortens the distance between the plant and the object its tendril is
attached to. But there is a wrinkle to the coiling. If the tendril coils too
much it can over coil, so it reverses the direction of coiling from clockwise
to counter clockwise, or vice versa. That leaves a little uncoiled “bridge” in
the middle where the change in direction takes place. Recently researchers at
Harvard tried to physically model this coiling phenomenon, inspired by looking
at cucumber tendrils. They created a physical model of the cucumber tendril that
behaved in a similar way and, as a byproduct, applied for a patent for a new
type of spring. The details of their research are explained
in this article from The Guardian.
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| Tendril of Purple Passion Flower Note the reversal of coiling midway between the upper and lower attachment points. |
At the bottom of the Dunson Garden there are four kinds
of plants currently blooming: Purple Milkweed, a large Elderberry tree, a large
group of Smooth Coneflowers and a big cluster of Curlyleaf Yucca.
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| Yucca flower; stamens encircle the pistil in the center. |
Two weeks ago we talked about the mutualistic
relationship between the Yucca moth and the Yucca plant. The moth is the only
insect that can pollinate the Yucca flower. The developing seeds of the Yucca are
the sole food of the Yucca moth caterpillar, so by pollinating the flower the
moth secures food for her offspring. The plant she pollinates gets to produce
seeds, some of which she must sacrifice to feed the caterpillars. As long as
there aren’t too many caterpillars both partners benefit. But if the caterpillars
overwhelm the number of seeds the plant will abort the flower they are feeding
in. It’s a dynamic relationship in which both parties benefit and there are
sanctions imposed if either one gets too greedy.
The bed of Smooth Coneflowers (Echinacea laevigata)was teeming with bumblebees. At one time it
looked like there was one bee on each blossom.
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| Hairy Cat's-ear a composite flower with only ray florets |
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| Hairy Cat's-ear basal leaf If the spots are part of the leaf it would explain the other common name. |
Up the hill the Hairy
Cat’s-ear (Hypochaeris radicata) is
still blooming. The generic name, Hypochaeris, is derived from the Greek for “cat’s
ear,” which explains part of the common name. The “Hairy” part of the name
probably refers to the hairiness of the basal leaves. Some books call it Spotted
Cat’s-ear, which is an even more mysterious reference, at least until I looked
at Ted’s photo of a leaf. There are a number of dark spots on it, so perhaps
that’s the origin of the other name. No matter the name, it is a recent
invasive species from Eurasia. Linda remembers never seeing it when she moved
to Athens, but, by 1978, it had spread to many disturbed open areas like
roadsides and lawns. Its wind dispersed seeds enabled its rapid spread.
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| Imported Fire Ant nest, disturbed by scraping the crust off. The white spots are the brood being taken to shelter by the worker ants. |
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| Central portion of photo above enlarged |
Imported Fire Ant
(Solenopsis invicta) mounds are common in lawns, pastures and other disturbed
areas, especially after rains when the workers have carried wet clay crumbs to
the surface to clean out their collapsed tunnels. They also carry their brood
(a collective term for the eggs, larvae and pupae) up near the surface, where
it is warmer during the daytime. There, just under a thin layer of dirt, the
brood is warmer and develops faster. At night, when the surface temperatures
drop, it is warmer lower in the nest and the brood is taken back down into the
nest. We disturbed a nest by quickly moving a finger across the surface,
revealing many worker ants and their brood. They quickly gather up the brood
and carry them out of sight. At one nest we saw, in addition to the workers and
the brood, sexually mature, winged ants that are much larger than the workers.
This is an indication that mating flights are about to take place, so this is a
good time to explain the colony life cycle in Fire Ants.
When the conditions are right (high humidity, temperature
> 70) the virgin, winged males and females emerge from all the nests in an
area and embark on their mating flights. The virgin female ants mate only once.
(In other kinds of ants the future queens may mate with multiple males.) After
mating the lucky males die. Unmated males also die within a few days. The mated
females store the sperms they received in special organs in their reproductive
tracts. This sperm will last their entire life, as long as seven years. Each
female independently flies about seeking a favorable area to build a nest. She
lands and clips off her wings and then excavates a small chamber in which she
lays a few eggs. This is the beginning of her nest and new colony. She survives
by eating some of her eggs and internally digesting her flight muscles. She
will never leave her nest. The eggs hatch and the new workers forage for food
and feed the queen and her brood. As the colony grows in size and spring
approaches the queen produces males and the workers begin to feed some of the
brood more food. The queen can determine the sex of her offspring. If an egg is
fertilized it will become a female. Whether it becomes a sterile worker or a
virgin queen depends on the amount of food it is given by workers. If the egg
the female is laying is not fertilized it becomes a male. When the conditions
are right another mating swarm will occur. A healthy colony can swarm several
times a year.
The queen of the colony can live for as long as 7 years
and produce as many as 1000 eggs a day. Workers live as long as three month.
The above is the standard cycle for a colony with a
single queen. In such a colony the workers will kill another mated queen that
attempts to enter the colony. Such a colony is called a “monogyne” colony.
There is a modification to this pattern. One genetically
controlled variation in Fire Ants allows the colony to allow multiple queens.
In these “polygyne” colonies the nests are closer together and ants from one
nest can enter other nests without being attacked. It has been shown by Ken
Ross, a UGA professor who studies the Imported Fire Ant, that the difference
between the monogyne and polygyne is controlled by a single gene.
Prairie
restoration status. Linda
summarized the plan for converting this part of the hill to a “Piedmont Prairie,”
with herbs and grasses similar to what is seen in the experimental plot. The
remaining lawn, consisting mostly of Bermuda grass and Fescue, will be treated
with grass-specific herbicide. It will then be mulched with hay made up of
mostly Little Blue Stem grass, a typical prairie grass. Seeds of Little Blue
Stem will also be scattered within the mulch. Plugs of herbaceous plants,
propagated here in the Garden will also be planted. It will be necessary to
spray some of the boundary area plants that are especially aggressive (e.g.,
wingstems and dog fennel).
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| Birdwing Grasshopper |
It’s encouraging to see our insect fauna finally making
an appearance. Our sharp-eyed young rambler, James, who has been with us for
the last three or four summers, spotted a large Birdwinged grasshopper (Schistocerca
sp.) and another rambler found a pair of green, mating stinkbugs (Family Pentatomidae).
