Floating World

 

A mixed group of floating water plants.  
Palm Beach County, Florida

Afloat on the water, plants experience two dramatically different worlds.  One is bright, hot and dry, the other is dim, cool and wet. Some floating plants are rooted to the bottom and others sail about, moved by wind or current.  Many floating plants survive and thrive at this odd interface and we will look at just a few. 

Sargassum fluitans, Broad-leaf Gulfweed, floating in the clear blue water
of the Gulf Stream off Cape Hatteras, North Carolina. 

One marine floating plant is a seaweed in the genus Sargassum.   This brown alga floats at the surface of the ocean carrying out photosynthesis.  Sargassum never attaches to the ocean floor and can drift for long distances.  Sargassum supports many species of animals and microbes and will often wash up on Atlantic or Gulf beaches.  The North Atlantic Gyre is in the center of the ocean and is bounded on all sides by currents.  In the gyre, an area called the doldrums, have calm winds and little current.  Here vast amounts of Sargassum accumulates to form the Sargasso Sea.  Unfortunately, plastic trash also accumulates in the gyre and makes the North Atlantic Garbage Patch. 

 

A fresh-water swamp with a mix of floating plants. 
Colleton County, South Carolina. 

Freshwater ecosystems have many floating plants.  They generally grow in still or slow-moving water found in swamps, ponds, marshes and lakes. Fragrant Waterlily, Nymphaea odorata, grows throughout Central and North America.  This plant has a rhizome, an underground stem, rooted in the bottom of the body of water.  Long petioles bear the large, round, notched leaves that float on the surface.  Nymphaea odorata makes beautiful, fragrant white flowers that give the plant its name. The upper surface of the floating leaf has a waxy layer to prevent water loss.  Stomates, pores that allow CO₂ to enter and O₂ to exit the leaves are also on the upper leaf surface.  The lower leaf surface has neither stomates nor a waxy layer since that side of the leaf is in the water.    

Fragrant Waterlily (Nymphaea odorata).
Rowan County, North Carolina.

Another rooted water plant with floating leaves is Nuphar advena, Spatterdock.  This plant is found in both the old and new worlds and has large leaves that are deeply cut at the base.  Spatterdock makes a compact yellow flower that extend above the surface of the water.  

Spatterdock (Nuphar advena). Collier County, Florida.

Water-shield, Brasenia schreberi, is yet another water plant that is rooted to the bottom.  Its elliptical, shield-shaped leaves are smaller than those of Fragrant Waterlily and Spatterdock.  Water-shield leaves can grow in dense clusters in their still water habitat.  The leaves produce mucilage on the lower surface that may protect the plant from herbivores and prevent algal growth.  All three of these rooted water plants have air spaces in their leaves to give them buoyancy and to help transfer oxygen to the roots that may be in the anaerobic mud bottom of a pond.   

Water-shield (Brasenia schreberi).
Georgetown County, South Carolina.

Many floating plants are not rooted to the bottom but float freely on the surface.  One plant with this way of life is Water Lettuce, Pistia stratiotes. This pan-tropical plant is in found in the Southeastern United States and may be an introduced species.  Water Lettuce has a rosette of leaves that resembles a head of lettuce. Pistia stratiotes is a fast-growing plant and may cover the entire surface of ponds or canals and cause fish kills.  

Water Lettuce (Pistia stratiotes) floating in a pond.
Palm Beach County, Florida.

Water Lettuce and the water fern Salvinia minima. 
Palm Beach County, Florida. 

Common Duckweed, Lemna minor, a tiny, free-floating plant has leaves that are just a few millimeters in diameter with each plant having a single root. It is found in ponds and ditches worldwide.  Common Duckweed rarely flowers and the plant reproduces by fragmentation.  Lemna minor grows rapidly and has a number of uses.  Common Duckweed is used as an animal feed, it is important in wastewater treatment because it removes inorganic nutrients and it accumulates toxic heavy metals.  

Common Duckweed (Lemna minor) in a swamp forest. 
Rowan County, North Carolina.

Salvinia minima is a floating fern.  Its common name, Water Spangles, describes its sparkling appearance on the surface of a pool.  Salvinia minima has round floating leaves that are ¾ inch in diameter and hairs on the upper surface that repel water.  This fern has no roots but it does have highly branched underwater leaves that play the role of a root system.  Salvinia minima is native to Central America and the West Indies.  It is considered and invasive species throughout the Southern United States. 

Water Spangles (Salvinia minima) a water fern growing in a cypress swamp.
Palm Beach County, Florida.

Golden Club, Oronitum aquaticum is our final floating plant. It grows in slow moving streams and ponds in the Eastern United States and is rooted in the mud.  Another common name for this plant is Never-wet because its leaves repel water.  Golden Club has unique flowers that gives the plant its name. The flowers have white stalks tipped with tiny golden blooms.  

Leaves and flowers of Golden Club (Oronitum aquaticum).

Rowan County, North Carolina. 

A drop of water beaded up on the leaf of Golden Club. 
This water repulsion shows why this plant is also called Never-wet. 
Rowan County, North Carolina.

Plants in the floating world range from the oceans to freshwater ponds.  They may be as tiny as Common Duckweed or as large as Fragrant Waterlily.  But all these plants share adaptations that allow them to live at this intersection of air and water. 

Wildflower or Weed?

 

Bird's Eye Speedwell (Veronica persica). A small, early spring 
wildflower from our yard.  Rowan County, North Carolina. 

Spring is upon us and in our yard delicate wildflowers are popping up and blooming.  Our lawn is not a smooth monoculture of Bermuda grass. The lawn does have some grass but it also has lots of wildflowers, that is weeds. A definition of a weed is "a plant that is growing where someone does not want it".  Lots of plants that we call weeds are adapted to living in disturbed habitats. Our lawns and roadsides mimic the natural environment where these plants thrive.   

Flowers and fruits of Cardamine hirsuta, Hairy Bittercress.
Rowan County, North Carolina.

An early and dainty wildflower is Cardamine hirsuta, Hairy Bittercress.  This small plant has flowers with flower parts in fours including its white petals.  The fruits of Hairy Bittercress, called siliques, are cylindrical and contain a single row of tiny seeds.  Cardamine hirsuta is in the family Brassicaceae, a group that includes many important vegetables including mustard, cabbage, broccoli and turnips.  Hairy Bittercress is native to Europe and has spread around the world, including much of the United States.   

 

Flowers of Hairy Bittercress with their four 
petaled flowers.  Rowan County, North Carolina.

Two other early lawn weeds are in the mint family, the Lamiaceae.  Lamium purpureum (Red-dead Nettle) and Lamium amplexicaule (Henbit) are both small herbaceous plants that make hooded, purple flowers.  Lamium flowers are bee pollinated and provide nectar for the early emerging insects.  The common name, Red-dead Nettle, refers to the superficial resemblance of Lamium purpureum to true nettles in the genus Utrica.  However, Lamium purpureum does not sting, hence the name dead-nettle.   Both these species of Lamium are found throughout North America but originated in Eurasia. 

 

The mint Lamium purpureum or Red-dead Nettle.
Rowan County, North Carolina. 

A large stand of Henbit, Lamium amplexicaule.
Rowan County, North Carolina. 

Our yard is graced by two species of Veronica in early spring.  The common name of Veronica is Speedwell and they are classified in the plantain family, the Plantaginaceae.  Veronica hederifolia, Ivy-leafed Speedwell is a small plant with tiny blue flowers.  Veronica persica, Bird’s-eye Speedwell, flowers are a little larger than the Ivy-leafed Speedwell and are also blue.  Both these Speedwells have darker blue lines on the petals called nectar guides.  Insect pollinators like bees can see ultraviolet and these lines are dark ultraviolet arrows pointing to the flower’s nectary.  As the bee is sipping nectar it picks up pollen and takes it to the next Veronica flower.  Both Speedwells were introduced to North America from Eurasia. 

Ivy-leafed Speedwell, Veronica hederifolia.
Rowan County, North Carolina.

 

Veronica persica, Bird's-Eye Speedwell. This species has
larger flowers than the Ivy-leafed Speedwell. 
Rowan County, North Carolina.

The white flowers of Common Chickweed (Stellaria media) also appear in spring.  Common Chickweed flowers have five petals but because each petal is two-lobed the flowers appear to have ten petals.  Stellaria media is in the Caryophyllaceae, the same family as carnations.  Chickweed is native to Asia and Europe and can be eaten raw in salads or cooked like spinach. 

 

Common Chickweed, Stellaria media, with its tiny white flowers.
Rowan County, North Carolina.

Sow Thistle, Sonchus oleraceus, like our native thistles, is classified in the Asteraceae, the sunflower family.  It is yet another spring weed that was introduced from Eurasia.  Sow Thistle grows in disturbed habitats. This plant is highly nutritious and eaten by people and pigs alike.  The flowers of Sow Thistle are yellow and resemble those of Dandelion (Taraxacum officinale).  The fruits of Sow Thistle are also like those of Dandelion and are dispersed on the wind. 

 

Sonchus oleraceus, Sow Thistle growing beside a road
in my neighborhood.  This member of the sunflower family is 
originally from Eurasia.  Rowan County, North Carolina. 

Close up of flowers and fruits of Sow Thistle.  The fruits of this plant can fly on the breeze. 
Rowan County, North Carolina. 

Azure Bluet (Houstonia caerulea) has delicate blue flowers with four petals and a yellow center.  Houstonia caerulea is a member of the Rubiaceae, a family that also contains the plants that give us coffee beans and quinine.  Unlike the other wildflowers already discussed in this blog, Azure Bluets are native to North American being found from Eastern Canada to the southern US.  

Azure Bluet, Houstonia caerulea growing in a lawn. 
Rowan County, North Carolina. 

A whole segment of the chemical industry is devoted to developing and selling weed killers.  We never apply them to our “lawn”.  After all, our yard is mostly weeds, or wildflowers.

Monarchs, Viceroys and Queens

 

A Monarch Butterfly (Danaus plexippus) feeding on 
Tropical Milkweed (Asclepias curassavica).
Rowan County, North Carolina.

I know, I know, another story about Monarch Butterflies.  I can’t help it.  Monarchs (Danaus plexippus) are large, brilliantly colored, poisonous and make an epic migration every year. Monarchs also belong to a mimicry complex, a group of butterflies that resemble each other.  This resemblance protects them from predators.  Monarchs are distasteful to birds because their larvae develop on milkweeds (Asclepias sp.).  Milkweeds make toxic compounds called cardiac glycosides that repel most insects but the Monarch larvae have evolved tolerance to these chemicals.  When a Monarch larva metamorphoses into the adult butterfly it retains the toxic plant compounds to repel birds. 

 

Monarch Butterflies migrating through the Black Mountain Gap below
Mount Mitchell, North Carolina.  These Monarchs were feeding on Aster sp. 
on their way to Mexico.  Yancy County, North Carolina.

Viceroys (Limenitis archippus) and Queens (Danaus gilippus) both bear a remarkable resemblance to Monarchs with their bright orange wings, striped with black and dotted with white.  Monarchs are found throughout North America and into Mexico.  Viceroys live in the eastern two thirds of North America and Mexico.  Queens have a more southern distribution along the southern border states of the US from Florida to California and into Mexico. 

 

A Viceroy Butterfly (Limenitis archippus) resting on a Tag Alder
(Ulnus serrulata). Viceroys and Monarchs are members of a mimicry complex.
Clayton County, Georgia.

The standard story of mimicry in these butterflies has the Monarchs being protected from bird predators by toxic cardiac glycosides.  Viceroys were supposed to be palatable to birds and avoid being eaten because of their resemblance to Monarchs even though they don't have chemical protection.  This type of mimicry, with a toxic model (Monarch) and a tasty mimic (Viceroy) is called Batesian mimicry.  Henry Walter Bates, a 19^th Century English naturalist who is the namesake for this mimicry, first described this relationship based on his study of South American butterflies. 

Recently researchers have shown the Monarch-Viceroy mimicry story is more complicated than originally thought.  Viceroy butterfly larvae often develop on willow (Salix sp.) leaves and can also be poisonous.  Willows contain toxic salicylic compounds related to aspirin.  The Viceroy caterpillars ingest these molecules and the adult butterflies may be unpalatable to birds.  Mimicry where two protected species resemble each other is called Müllerian mimicry, named for German zoologist Johann Müller.   Müller, like Bates, studied butterflies in South American in the 1800s and discovered this distinctive type of mimicry.  In Müllerian mimicry several protected species resemble each other and all are protected from predators.  Müllerian mimicry is why bees, wasps, yellow jackets and hornets all resemble each other. The yellow and black bodies of these insects send a clear message to leave us alone.  Monarchs and Viceroys (sometimes) are both chemically protected so their resemblance can be Müllerian mimicry.  

 

A Queen (Danaus gilippus) feeding on Oakleaf Fleabane (Erigeron quercifolius).
This butterfly is also a member of the mimicry complex with Monarchs and Viceroys.
Palm Beach County, Florida.  

Queens are closely related to Monarchs and their larvae develop on milkweeds and their relatives.  Queens are protected by the same cardiac glycosides found in Monarchs.  Viceroys were once thought to be Batesian mimics of Queens where their ranges overlap.  But since we now know Viceroys are chemically protected this is another example of Müllerian mimicry.   The Viceroy-Queen story in Florida is even more complicated.  In 2019 a group of American researchers found that in north Florida the Viceroy population is high and the Queen population is low.  There the Viceroys have a higher concentration of chemical defense compounds.  In south Florida Queens are abundant and Viceroys are rare and are not well protected.  But in central Florida both species are relatively abundant and the Viceroys have low concentrations of their protective chemicals.  With lots of Queens around, the Viceroys do not need as much of the toxic chemicals.  So, in central Florida, the Viceroy-Queen relationship changes from Müllerian to Batesian mimicry.  

 

A Monarch on Tropical Milkweed. 
Rowan County, North Carolina.

The work of both Bates and Müller on mimicry gave early, independent evidence for Darwin and Wallace’s theory of Natural Selection. This mimicry is on display for us to see in these brilliant butterflies. 

 

 

The Architecture of Trees

 

A towering Giant Sequoia (Sequoiadendron giganteum) in
Yosemite National Park, California.  Giant Sequoias are among the
largest trees in the world.  The huge trunk of this tree reaches about 200 feet
before branching. 

Winter is a great time to admire the architecture of trees.  Deciduous trees dropped their leaves in the fall and their structure is on display for all to admire.  The variety of tree shapes is astounding.  Some trees have towering trunks with their branches high in the air.  Others are small with multiple trunks.  Some trees look like vases or columns or pyramids, some weep.

 

A Bald Cypress (Taxodium distichum) with the pyramid shape. 
Like Christmas trees, this Bald Cypress is widest 
at the bottom and tapers toward the top.
Rowan County, North Carolina. 

A Red Maple (Acer rubrum) with many trunks growing from the base
giving it a vase-like shape. Rowan County, North Carolina.

Dwarf Weeping Cherry (Prunus subhirtella).  This small tree has
a short trunk and numerous contorted branches. The terminal branches
hang down and the tree appears to weep.
Rowan County, North Carolina. 

The branching pattern of trees has much to do with their shape.  Leonardo da Vinci, when he was not painting the Mona Lisa, designing helicopters or making breakthroughs in human anatomy, considered the branching of trees.  His fundamental insight about trees is that the cross-sectional area of the trunk is equal to the cross-sectional area of the branches.  So, if the main trunk of a tree has a cross-sectional area of 100 square inches and it branches into two main limbs, those two limbs will have a cross-sectional area of about 50 square inches each.  This pattern continues with all subsequent branches.  If you measure the cross-sectional area of the twigs they will still have a cross-sectional area of 100 square inches. 

 

Black Gum (Nyssa sylvatica) with a main trunk
and many limbs with branches. Rowan County, North Carolina,

Consider the branching of trees.  A branch may divide into two branches and each of those branches could branch into two more branches.  This pattern is repeated many times in a tree.   Iterative branching goes a long way in explaining the shape of trees.  Trees are natural examples from the field of mathematics called fractal geometry.  The Polish-French-American mathematician Benoit Mandlebrot coined the term fractal in the late 20^th century to describe objects that have similar structure at different scales.  If you look at a whole tree, you find the same basic pattern in the limbs, branches and twigs. 

 

A fractal tree. Virtual trees like this can be produced by a
couple of dozen lines of code. This mathematical tree bears
a striking resemblance to a biological tree. 
https://commons.wikimedia.org/wiki/File:Fractal_canopy.svg

The fractal branching pattern of an American Sycamore
(Platanus occidentalis). Rowan County, North Carolina.

Fractal tree canopy in winter. Rowan County, North Carolina

The reason a tree makes all those branches is to provide the scaffold for the leaves.  A large tulip poplar tree (Liriodendron tulipifera) may have over 100,000 leaves.  Each leaf weighs only a few grams but during summer, particularly when the leaves are wet and the wind is blowing, they put a tremendous stress on the tree.  This load is supported by up to fifteen tons of wood in the trunk, limbs and branches. 

 

Leaves of Tulip Poplar (Liriodendron tulipifera) in high summer.
The hundreds of thousands of leaves are supported by the many
small branches of the tree.

Some trees have tall straight trunks and limbs extending out to the side.  Pine trees (Pinus sp.) are good examples of this structure. When a side limb dies or is broken off, the tree continues to grow in diameter until the broken limb is entirely overtaken and is now inside the trunk.  This old limb may be invisible from the outside but, if the tree is converted to lumber, the old branch is seen as a knot in the wood. 

 

Shortleaf Pines (Pinus echinata) with tall, straight
trunks and limbs branching off.
Rowan County, North Carolina. 

A dead limb on a Shortleaf Pine.
Rowan County, North Carolina.

The knot in a pine 2x4 is a branch the wood grew over as the
tree increased its girth.
Rowan County, North Carolina. 

Spring is coming on and soon the trees will be cloaked in green.  But the deep structure, the architecture of trees, will still be there.

Nothing Like a Beach

A stormy day on the beach at Spanish River Park, Boca Raton, Florida.
This part of Floirda is called the Gold Coast because the sand takes on a golden hue
from shell fragments mixed with the white quartz sand. 

There is nothing like a beach.  The infinite horizon, the ever changing light, the sound and even the smell make beaches irresistible.  About 40% of the US population lives near the coast.  But, even at a beach lined with high-rise hotels, if you turn you back on the buildings there is a wet wilderness running to the vanishing point.  This interface between land and ocean is harsh.  Abundant water, salt and light mean unique plants and animals are found on beaches.  Some are sea creatures that wash up.  Some are denizens of the land that occupy the last real estate before the ocean.  Others are highly adapted to living on this demanding edge of the continent.  

I grew up in South Florida, a mile and a half from the Atlantic.  The beach was part of the fabric of my life. Now I live hours from the nearest beach and it is always special when I get to a beach. This blog will examine some beaches and the creatures on them.  

Florida

Lesser Black-backed Gull (Larus fuscus) on Lake Worth Beach, Florida.
This large gull winters in the Southeastern United States where its
numbers are increasing. 

Royal Tern (Thalasseus maximus) on Lake Worth Beach, Florida. 
Royal Terns are year-round residents from North Carolina to the tropics.

Sandwich Tern (Thalasseus sandvicensis) at Spanish River Park, Boca Raton, Florida.
This tern is smaller than the nearby Royal Terns.  It has characterisitc yellow tip on
its beak, as if the bird dipped its bill in mustard.  

Two White Ibis (Eudocimus albus) feeding in the surf at Canaveral National Seashore,
Florida. These waders are found in fresh, barckish and salt water.

Portugese Man-o-War (Physalia physalis) at Boynton Beach Park, Florida.
This relative of corals and jellyfish is the bane of swimmers. 
It has an irredescent blue float and trails tentacles in the water
that bear stinging cells.  A person unlucky enough to
brush against a tentacle will receive a painful sting.

South Carolina

Sunset at Surfside Beach, South Carolina. The sand on the South Carolina
beaches is gray and made of sand washed into the Atlantic
from rivers. 

Ring-billed Gull (Larus delawarensis) on Surfside Beach, South Carolina.
This is the most common gull in the Southeast.  

Sanderlings (Calidris alba) in the sunrise surf at Huntington Beach State Park,
South Carolina. Sanderlings are small, gray and white shorebirds that run up and down the 
beach like a windup toy, following the breaking waves.  The name Sanderling comes from
Old English and means "sand plower".  And they do plow the sand, looking for 
 the small animals they eat. 

A dead Common Loon (Gavia immer) washed up on the sand at Huntington Beach
State Park, South Carolina.

Ghost Crab (Ocypode quadrata) at Huntington Beach State Park,
South Carolina.  These crabs are sand-colored and make burrows 
on the beach above the high tide line.  They usally feed at night but
this one was out on a cloudy day.  The genus name, Ocypode, means
swift footed and so they are.  

This may look like an aerial view of the Sahara Desert but these
dunes are only two inches tall.  Huntington Beach State Park,
South Carolina. 

West Coast

The rocky shoreline of the Monterey Pennisula, California. 

Bull Kelp (Nereocystis luetkeana.) on a sandy beach, Monterey Pennisula,
California.  These giant Brown Algae may reach 100 feet in length.
Kelps make extensive forests in the Pacific off California.  The round
structure is a float the alga fills with gas including carbon monoxide. 
The float keeps the kelp near the surface so it can carry out photosynthesis. 

 

Cannon Beach, Oregon has a sandy beach with sea stacks, large
rocks produced by coastal erosion. This location was used in the great
kid's adventure movie, The Goonies.

The most amazing thing I have ever seen on a beach was a Walrus
(Odobenus rosmarus).  This giant marine mammal was hauled out on the shore of
the Bering Sea, south of Nome, Alaska.  Walruses use their tusks to open breathing
 holes in sea ice and pull themselves up onto ice floes. 

Hawaii

The Hawaiian islands are ringed by beautiful beaches. 
I think the most spectacular are the black sand beaches. 
They are made of eroded sand and stones from lava. 
This black sand beach was at Punalu'u County Beach Park
on the Big Island. 

A Green Sea Turtle (Chelonia mydas) sunning on a black beach.
Punalu'u County Beach Park, Hawaii. 

Black sand beach backed by Coconut Palms (Cocos nucifera).
Punalu'u County Beach Park, Hawaii. 

When I was a kid going to the beach with my family, we would swim and snorkle, body surf and beach comb.  Now, I am not swimming or body surfing or snorkeling as much.  But I still like to walk the beach, looking at the water and seaweed and all the animals at the end of the land.