Today's
Ramble was lead by Linda Chafin and written by Linda with note-taking assistance by Sue Wilde. We are indebted again to Rosemary Woodel for providing the photographs that accompany this post.
Announcements: Bob Ambrose shared the
publication of his new book of poetry, Journey
to Embarkation, poems written mostly before he began writing about nature.
He read a poem for us, The Night Music of San Rafael de Guatuso, which was set in Costa
Rica and featured the call of the Dusky Nightjar, a bird closely related to and
sounding much like our own Whip-poor-will. Bob notes that his book is also
available online from two sources: Amazon and Parson's Porch & Book
Publishing Co. (Bob will also have some copies available to Ramblers at a reduced
cost.)
23
people appeared for the Ramble today.
Today's route: We wandered
down the Orange Trail Spur to the floodplain, turned right at the base of the
slope, and entered the Powerline Right-of-Way.
Linda
announced that the theme for today’s walk would be plant classification and the
importance of learning the characteristics of plant families, which makes
identification to species a lot quicker and easier. She described some of the
divisions of the Plant Kingdom:
vascular
versus non-vascular, i.e. plants with vessels to transport water and nutrients
(most plants) versus plants without vessels (such as mosses and liverworts);
angiosperms
versus gymnosperms, i.e. flowering/fruiting plants versus
non-flowering/cone-bearing plants;
and,
finally, the division of flowering plants into dicots versus monocots. This
last split is most useful for those wanting to identify wildflowers.
Dicots
(more recently referred to as eudicots or “true dicots”) are the group of
plants with two seed leaves (cotyledons), net-veined leaves, and flowers with
their parts in 4s or 5s (of course, there are exceptions). Many dicots produce
woody tissue in trees, shrubs, and woody vines.
Monocots
are the plants with a single cotyledon, usually parallel-veined leaves, and
flowers with their parts in 3s or multiples of 3s. Monocots do not produce true
wood although some can grow quite tall, such as palms and Joshua Trees.
Within
the dicots and monocots, most field botanists focus on the level of classification
called the family, followed by genera (singular: genus), and species (a term
used as both plural and singular).
A note on taxonomy:
In plants the family names all have the same suffix, -aceae, pronounced "ACE-EE-EE" or "A-SEE-EE."
The subfamily names all end with the -oideae suffix, pronounced "OID-EE-EE."
The first family we stopped to look at was the Grass Family (Poaceae). Grasses have round, hollow stems (except at their leaf nodes). Their leaves have two parts: a blade that extends outward from the stem and a sheath that wraps around the stem. Their flower parts are in 3s but are very tiny and hard to see.
In plants the family names all have the same suffix, -aceae, pronounced "ACE-EE-EE" or "A-SEE-EE."
The subfamily names all end with the -oideae suffix, pronounced "OID-EE-EE."
The first family we stopped to look at was the Grass Family (Poaceae). Grasses have round, hollow stems (except at their leaf nodes). Their leaves have two parts: a blade that extends outward from the stem and a sheath that wraps around the stem. Their flower parts are in 3s but are very tiny and hard to see.
The
next family we encountered was the Sedge Family (Cyperaceae) which is often
mistaken for the grass family. The old jingle, ‘sedges have edges, rushes are
round, and grasses have joints all the way to the ground,’ was invoked to
describe the differences among the stems of the 3 main grass-like plant
families: Cyperaceae, Juncaceae, and Poaceae.
Emerging
from the woods onto the powerline right-of-way, we stopped to look at plants in
the Aster or Composite family (Asteraceae). This is the largest plant family in
the world, with more than 23,000 species and is found on every continent. Their
global success is attributed to the structure of their inflorescence, a head of
many closely packed flowers. A single, short visit by a pollinator results in
the pollination of many flowers. The head consists of a whorl of (usually
sterile) ray flowers, a central disk or cone of tiny but fertile disk flowers,
and, holding this all together from beneath, a series of tiny green bracts in a
cup-shaped or cylindrical whorl (these bracts are called phyllaries). The
sterile ray flowers are usually colorful and showy and attractive to
pollinators. The disk flowers actually produce the seeds. The Aster Family
plants we examined were Rough Daisy Fleabane (Erigeron strigosus) and
Wingstem (Verbesina alternifolia).
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| Wingstem ray and disk flowers |
Later
in the ramble, we encountered a few Aster Family plants that did not get the composite
memo: they lack either the ray flowers
or the disk flowers. In the case of thistles (Tall Thistle, Cirsium altissimum), there are no ray flowers and the bright pink disk
flowers are large and showy. In the case of Cat’s Ear (Hypochaeris radicata) and
Carolina Desert Chicory (Pyrrhopappus
carolinianus), the disk flowers are
missing and the head is filled with fertile ray flowers. The whorl of green
phyllaries is still present, though, and holding the heads together in both
these inflorescence types. We also looked at two other common members of the
Aster Family in flower late in the Ramble: Elephant’s Foot (Elephantopus tomentosus) and Frostweed (Verbesina
virginica), which Ramblers know from
their early winter “frost flowers.”
The
next species we stopped to examine was Wild Senna (Senna marilandica), a
member of the third largest angiosperm family, the legume family – Fabaceae.
Like nearly all members of this family, Wild Senna has compound leaves with 3 -
many leaflets. Also like many species of legumes, Wild Senna has extrafloral
nectaries (EFNs). EFNs are nectar-producing glands that are not associated with
flowers, but are found on leaves and stems. In most cases, EFNs attract ants
that happily lap up the nectar and, to protect this source of carbon-rich food,
attack other insects that try to visit the plant. As a result, insects that
would be inclined to eat the leaves of the plant are driven away – a classic
example of mutualism. The EFNs on the Wild Sennas we looked at in the powerline
right-of-way nearly all had ant visitors gathered around them.
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| Ant sipping nectar from Wild Senna EFN |
We
also discussed the fact that the legume family is divided into 3 sub-families
that, despite their flower differences, all produce the same kind of fruit – a
bean pod. Genetically, the 3 subfamilies are similar enough to warrant lumping
them into a single family. Mimosa Tree (Albizzia julibrissin) and Sensitive
Brier (Mimosa microphylla) are
examples of the subfamily Mimosoideae that everyone is familiar with. Wild
Senna and Sicklepod (Senna obtusifolia)
are examples of the second subfamily (Caesalpinoideae) that most of us had seen
before. And last, but not least, the Faboideae subfamily, is the largest of the
subfamilies and the most familiar, with well known species such as Redbud (Cercis canadensis), Wild Indigo (Baptisia spp.), Wisteria (Wisteria spp.), and Kudzu (Pueraria montana). Here are photos of
the characteristic flowers of the three subfamilies (photos by Hugh and Carol
Nourse):
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| Sensitive Brier; subfamily Mimosoideae |
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| Wild Senna; subfamily Caesalpinoideae |
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| Wild Indigo; subfamily Faboideae |
The
next family we encountered was in the form of Smooth Buttonweed (Diodia virginiana), a member of the
Madder or Coffee Family – Rubiaceae. In temperate zones, the Coffee Family is
represented by only a few herbs and fewer shrubs, but is diverse and well
represented in the tropics where most of its members are shrubs or trees. This
is typical of many plant families: the closer you get to the equator, members
of a given family are more likely to be woody plants. Species in the Coffee
Family in our part of the world are characterized by opposite or whorled leaves
and flowers with 4 symmetrically arranged lobes (occasionally 5).
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| Buttonweed |
Next,
we stopped to look at Mountain-mint (Pycnanthemum
pycnanthemoides), a member of the Mint Family. Like other members of the
Mint Family, this species has square (four-angled) stems, opposite and entire
leaves, and a tubular flower with two, spreading lips. In most mint flowers,
the upper lip is erect or curved over like a hood, and the lower lip is dotted
or striped with “landing strips” to guide pollinators to the nectar held at the
base of the flower tube. Typically, mints have strongly aromatic leaves (think:
basil, thyme, oregano, sage, etc).
Mountain-mints
have a bracing, medicinal smell like Vapo-Rub.
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| Mountain-mint |
We
began to notice more insects at this point, spotting an Assassin Bug with its
well developed forelimbs, and a pretty, bristly yellow caterpillar. It’s called
a Yellow Bear Caterpillar and is the larval stage of the Virginia Tiger Moth (Spilosoma virginica). The moth itself is
a lovely, cottony white creature with wings that conceal a yellow-and-black marked
body.
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| Virginia Tiger Moth caterpillar |
Jeff
Jackson talked to us about Cicadas, which were beginning to “warm up their
fiddles” as the temperatures rose midmorning. The Annual Cicada, whose throbbing
sound somehow captures the essence of late summer heat and humidity in Georgia,
emerges every year from underground, where it has spent two years as a nymph. The
Periodical Cicadas, with their legendary, predator-overwhelming emergences, spend
long years underground as nymphs and emerge as enormous broods every 13 or 17
years.
An
article in Science Daily explains how cicadas make their huge, head-filling
sound:
“To
understand how the cicada makes its sound, you would have to imagine pulling
your ribs to the point of buckling collapse, releasing them and then repeating
that cycle. If your body were like that of a cicada, he explained, you would
have a thick set of muscles on either side of your torso that would allow you
to cave in your chest so far that all your ribs would buckle inward one at a
time into a deformed position. Releasing the muscle would allow your ribs to snap
back to their regular shape and then pulling the muscle again would repeat
this. The cicada repeats this cycle for its left and right sides about 300 to
400 times a second.” "Secrets of
the cicada's sound." ScienceDaily,
30 May 2013. <www.sciencedaily.com/releases/2013/05/130530152846.htm>.
If that is not clear enough here's the description from one of last year's rambles:
"If you gently hold a cicada by its thorax it will make a loud buzzing sound and flap its wings in an attempt to escape. The sound is not made by the wings. Cicadas have special sound producing organs called tymbals, located on each side of the body on the first segment of the abdomen. Each tymbal is a stiff, circular membrane, like a drum head to which a muscle is attached near the center. When the muscle contracts the membrane is put under tension. and when the muscle relaxes the membrane returns to its resting position with a "snap." It's like the sound you hear when you open a new jar of jam and the lid pops up when the seal is broken. The droning noise of the cicada is produced by very rapid repeated contraction of the tymbal muscles. The sound is amplified by a hollow resonating chamber that surrounds each tymbal organ. The individual snapping sounds merge together to make a loud, droning buzz.Most people are surprised when they hear how loud a noise such a small insect can make."
"If you gently hold a cicada by its thorax it will make a loud buzzing sound and flap its wings in an attempt to escape. The sound is not made by the wings. Cicadas have special sound producing organs called tymbals, located on each side of the body on the first segment of the abdomen. Each tymbal is a stiff, circular membrane, like a drum head to which a muscle is attached near the center. When the muscle contracts the membrane is put under tension. and when the muscle relaxes the membrane returns to its resting position with a "snap." It's like the sound you hear when you open a new jar of jam and the lid pops up when the seal is broken. The droning noise of the cicada is produced by very rapid repeated contraction of the tymbal muscles. The sound is amplified by a hollow resonating chamber that surrounds each tymbal organ. The individual snapping sounds merge together to make a loud, droning buzz.Most people are surprised when they hear how loud a noise such a small insect can make."
A
large, hairy, heavily fruiting Poison Ivy vine (Toxicodendron radicans) caught our eye and prompted a discussion of
woody vines and their ecology. Woody vines (lianas) are found in many plant
families and are an example of convergent evolution: the process whereby
unrelated organisms evolve similar structures or life strategies as a result of
adapting to similar environments. Woody vines rely on trees to lift them up
into the air where the sunlight, pollinators, and seed dispersers are likely to
be. Since they don’t have to invest so many resources into producing structural
tissue (like a tree does), woody vines can devote themselves to producing more
leaves (photosynthetic surfaces) and reproductive organs. Although not
technically parasites, woody vines do compete with their “hosts” for nutrients,
sunlight, and air, and have been shown in the tropics to inhibit growth of
their hosts.
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| Poison Ivy fruiting |
A
single Loblolly Pine (Pinus taeda)
seen along the edge of the powerline ROW supports four different species of
common woody vines: Virginia Creeper (Parthenocissus
quinquefolia), Trumpet Creeper (Campsis
radicans), Cross Vine (Bignonia
capreolata), and Poison Ivy. The differences in their different climbing
strategies could be clearly seen: aerial
rootlets on Poison Ivy and Virginia Creeper, tendrils on Cross Vine, and
twining stems (Trumpet Creeper).
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| Virginia Creeper attaches by "fingers" |
Two
members of the Milkweed Family were seen today in flower, both in the
powerline: Climbing Milkweed (Gonolobus suberosus), with its twining
stems and yellow-and-maroon flowers, and Butterfly Weed (Asclepias tuberosus), with its brilliant orange flowers.
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| Climbing Milkweed flower |
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| Butterfly Weed flowers The tiny bee is getting nectar but can't pollinate the flower - it's too small. |
The
former has the milky latex for which the family is named; the latter lacks
latex. The latex, which is produced and circulated outside the plant’s vascular
system, contains the toxin compounds which make the Monarch butterfly larvae
poisonous to birds.
Heading
back to the Visitor Center, we took a look at the last family of the day, the
Mallow Family – Malvaceae. An economically important family, the Malvaceae
includes cotton, okra, and hibiscus, including the old fashioned landscape
plant, Rose-of-Sharon or Althea (Hibiscus
syriacus). Two truly spectacular
mallow species were blooming like crazy at the lower end of the Dunson Garden: Rose Mallow (Hibiscus moscheutos), with its white, purple-throated flowers, and
Red Hibiscus (Hibiscus coccineus),
with huge, deep red flowers.
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| Red Hibiscus flower |
We
took a look at the characteristic arrangement of Mallow Family reproductive
parts. The stalks of the stamens are fused into a column that surrounds the
pistil and projects well out from the center of the open flower. Near the top
of the column, the anthers curve outwards. Above the stamens, the stigmas
emerge at the tip of the column. We tried to figure out how pollinators, in
their quest for nectar, manage to brush against both the anthers and stigmas,
which seem widely separated from the “eye” of the flower where nectar is
produced in most flowers. A bit of internet searching later revealed that
Hibiscus flowers don’t produce nectar, so the pollinators are not bumbling
around at the base of the flower at all. Pollinators are interested only in the
pollen and, in their climbing around the top of the column, manage to transfer
pollen. Whew.
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| Rose Mallow stamens and pistil; the dark spots on the stigmas are pollen grains. |
Finally,
we took a look at another characteristic feature of the Mallow Family: the
epicalyx. The flower has the typical whorl of colorful petals and green sepals,
but surrounding the base of the calyx is another whorl of 8 or 10 narrow, green
structures that curve up. Function? Who
knows? But this is another example of those ubiquitous structures called
“bracts” that we see in so many flowering plants. A bract is a broad term used
to describe any leaf-like structure associated with (but not part of) a flower,
and can take a variety of shapes and sizes and colors (think: red leaf-like
things surrounding poinsettia flowers).
