Tuesday, August 2, 2016

Ramble Report July 28 2016



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.

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). 

 
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.
 
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):

 
Sensitive Brier; subfamily Mimosoideae
Wild Senna; subfamily Caesalpinoideae
 
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).

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.

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.

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."
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.

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).
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.

Climbing Milkweed flower
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.

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. 

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).


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