Red Mangrove Embryos Bob Bob Bobbin’ Along

Rhizophora mangle

(Rhizophora means root bearing.  Mangle is Spanish for mangrove.)

Rhizophoraceae

Red Mangroves astound in many ways. One of the is the embryo.   The Red Mangrove embryo bobbing in the sea looks like a purposeful eel swimming vertically with its head above water.  Before getting far into the swimming, a few words on the embryo’s nuts and bolts.

A normal fruit on any other plant contains one or more seeds, and each seed in that normal plant houses a tiny embryo destined to grow into a new oak tree or orchid.    But Red Mangrove is not normal.   It makes a small rusty-leather fruit the size of a strawberry containing two seeds., one of them surviving.   So far so good, but now it gets weird.  The seed sprouts while the fruit still dangles from the parent tree.  The resulting embryo, resembling a large green bean, grows forth from and eventually dwarfs its fruit and may reach about a foot long and a half-inch in diameter dangling from the tree, the original fruit forming a brown cap around the green embryo’s attached upper end.

Embryos looking like green beans hanging on the parent tree.  The fruits are the brown caps at the upper ends of the embryos, which will soon drop free leaving the fruits behind on the tree.

 

When it finally comes time to go float to a new beach, the embryo breaks free, leaving its topmost parts (the cotyledons) behind within the fruit.   The part that falls into the sea then is an enormous root (hypocotyl) vertical below the water line with a little pointy tip exposed above the surface.  The pointy tip is the beginning of the top part of the future tree, the embryonic leaves, stems, and trunk.

Embryo floating in the Atlantic Ocean.

The pointy tippy top.

Why does the bottom end stay down while the top end stays up?    Not only is the bottom thicker, it also fails to have something the top possesses…open hollow airspaces.  The spaces clearly give the top end buoyancy, and perhaps have an additional role in gas storage and exchange.

Hollow spaces seen when the top part of the embryo is sliced open.

Here is the kicker.  The floating embryos cross oceans.   Their cruise can reportedly last a year.   For all those months the sojourners do not merely dormant and sleep their way across a thousand miles.  Rather, it looks like they live and breathe along the way.   Even when the root end down in the water turns brown, the upper end remains green and has chloroplasts.   There must be a reason the little swimmer keeps its head above water, no doubt the same reason I do…life support, gas exchange.   Those little submarines have circled the earth bobbing along with their  snorkel tops peeping above the waves.

 

Narrowleaf Yellowtops is a Pollen Pusher

Flaveria linearis (Flavus is Latin for yellow.)

Asteraceae

 

Must be October, the Yellowtops glow goldenrod autumn,  rich canary yellow in wet meadows and beyond.  They’re a friend to many pollinators.  Fact is, it is fun to get among the plants and see what visitors show up.

Photos by John Bradford

No need to linger on a boring point of physiology, but it is my duty to point out that this species is an intermediate in terms of C3-C4 photosynthesis.   The first, C3, is “normal” photosynthesis, typical of temperate plants.   The second, C-4 photosynthesis, is a biochemical and anatomical specialization typical of many tropical plants.   A plant has to be one way or the other, or does it?

Three native Flaveria species grace Florida:  Two are intermediate C3-C4. They are F. linearis and F. floridana which DNA shows to be a narrowly distributed Gulf Coast offshoot of the widespread F. linearis.  What’s interesting is that F. linearis ranges into cooler north Florida and into the hot tropics.  Is that the benefit of having mixed temperate-tropical photosynthesis?

Our third native species, F. trinervia, is not closely related to the other two.  It is C4 and evidently a South Florida visitor from a worldwide tropical distribution…with surprising (brief?) cool-climate extensions.

Members of the Aster Family often dish out pollen in more complex and intriguing ways than are conspicuous at first glance.  So it is for Narrowleaf Yellowtops. The flowers are reluctant to release pollen until an insect comes probing and stomping.  Bug-pokes cause the little blossom to push out pollen within seconds of contact.   Watch it happen in the brief video below where a fake insect provokes pollen expulsion.

Pollen-pushing video. Be patient, the action is episodic and subtle:  PUSH HERE

 

Redroot Roulette

Carolina Redroot, Lachnanthes caroliniana

(Lachnanthes means woolly flower.)

Haemodoraceae

Carolina Redroot is famous for its namesake red roots.   Been there, done that:  CLICK

This wetland bleeder hangs around where feral hogs snuffle the earth.   Correlation does not show cause, however.   Do the hogs seek out the redroot?  Do they spread it?   Or does the plant happen to grow in mudholes hogs fancy for other reasons? I don’t know. And for this moment, I don’t care, because what I wish to discuss are the unusual flowers, visited at least by bees, wasps, and butterflies.

The butterflies come for nectar, and perhaps the bees come mainly for pollen.  Somebody is going to have to sit a long time in a marsh with camera, binoculars, and bug net to tell the full story of Lachnanthes pollination.

What’s  weird about the flowers is that seen from the side the style with its pollen-receiving stigma is bent outside of the floral center, at about the same height as the pollen-releasing anthers.

Side view of woolly flowers. Anthers are dusty yellow. Stigma marked with blue line.

Flower from above. Three anthers yellow. Style green angled up and left.

Seen from above, the stigma juts out to the side about as far as the likewise bent anthers do.  Picture the flower as a clock face.  In the photo above the anthers are at 12, 5, and 7 o’clock releasing dusty yellow pollen.  The green style with pollen-catcher stigma at its tip is at 10 o’clock.      The stigma is in a spot where you’d reasonably expect an anther. Within an inflorescence, the bent stigmas point in every direction.

What’s up with that?  One answer, not original with me, is that the stigma is out of the way of all the sundry pollinators, but it seems there is more to it.  Given that the stigma occupies an “anther position,” an insect visitor is as likely to contact the stigma as any single anther.   Visitors approach the flowers oriented variably.   Spot on the insect pollen-dusted on a different flower will occasionally hit the stigma spot.  Twenty-five percent of the flower touches will be pollen drop-off, the other 75 percent will be pollen pick-up from the insect’s standpoint. This presumably accomplishes two things:

Accomplished thing 1. Accommodation of the diverse floral visitors.   All manner of bees, wasps, butterflies, and who knows what can play redroot-roulette, even perched on one flower  sipping nectar from another, or while feeding vertically as well as horizontally.

Accomplished thing 2. The roulette system may help promote cross-pollination. The incoming pollen is scattered on various insect body points from past visits to other flowers.  The different pollen-pickup points on the insect may carry pollen from multiple flowers.   The pollen deposited on a stigma is equally likely to have come from any of many flowers, all depending on where the roulette wheel stops.   A great system for mixing genes.

Redroot roulette.   The insect in the diagram picked up pollen on its right side and deposited that pollen on the next flower it visited.  Perhaps on its next stop it will drop off pollen from its left side, or from its chin.

Partial to redroot is the gray hairstreak butterfly. Today one was alternating between two plants, ignoring all others.  Most of its flower action is head down, for a reason.   The head is inconspicuous, while the fanny looks like a showy head, complete with orange coloration, false eyes, and best of all, fake antennae.

Head down on redroot. Fake antennae “up.”

An attacker is likely to go for the wrong end of the butterfly.  You might think a bird would gobble it up altogether, so what good is that fake head?  Entomologist Andrei Sourakov from the University of Florida found out.   The predators fooled are not big birds, but rather spiders.  They inject their venom into the wrong end of the butterfly.  Score one for the graystreak.

Sipping nectar

The rear end with false eyelashes.

BRIEF VIDEO  Watch the fake antennae wiggle: CLICK

THE END

 

 

Giant Whitetop, Broadleaf Painted-Sedge

Rhynchospora latifolia

(The name means wide-leaved beak-seed.)

Cyperaceae, the Sedge Family

Today’s wildflower is the chosen topic because it is so pretty and so eye-catching now in mid summer.   Rhynchspora latifolia decorates wet meadows and similar habitats standing 3 feet tall, waving its white and green flower heads above its neighbors.    Its smaller cousin Rhynchospora colorata has fewer white lobes, has the lobes not narrow abruptly at the green parts,  often grows more crowded, and prefers slightly less wet sites. According to reports R. colorata prefers alkaline as opposed to R. latifolia in acid locales, although I suspect that habitat difference is a bit overstated.  I’ve seen the two growing within a few yards of each other. Checking that out with a pH meter would make a great class research project.

The white “petals” are leaves (bracts).

What’s famously odd about the two rhynchosporas, additional Rhynchospora species not represented locally, and a smattering of other sedges and grasses is that they are fully or partially insect-pollinated species in huge plant families the textbooks generalize as wind-pollinated.  These are plants whose ancestors turned away from insect-pollination to wind, then the painted-sedges reverted to insects..

That’s like going back to golf after you throw away the clubs.  They had to re-evolve all the insect-related pollination apparatus starting from scratch.   Colorful petals were long-gone so the replacements are false petals made of white leaves (bracts) green at the tips.   Nectar is gone too, but there’s bright yellow pollen to attract and feed visitors.   What’s dismaying is that these flowers have re-evolved sweet floral perfume, released it seems only briefly in the morning. Most of the day they are without fragrance, but at perfume time they are surprisingly potent.

Morning seems to be the main time for action.  That is when all or most of the pollen-bearing anthers come forth, although they can persist all day.   That is also when most of the pollen-receptive stigmas come forth, although some may be apparent all day.

Spikelets (each thick white unit is a flower cluster).  Anthers are yellow. Stigmas are smaller, finer, and white.   Each spikelet is wrapped in bracts and contains several crowded flowers.

In each tiny flower the pollen-making anthers emerge from the bracts enclosing them and start releasing pollen before the pollen-receiving stigmas mature and emerge.  The anthers are bright yellow and prominent.  The stigmas are white, small, and held close to the flower head. Male-first is called protandry (PRO-tand-ry).  However, the flower head is made of hundreds of flowers, so that even if one flower is “male,” adjacent flowers may be in the female phase, or transitional.    Thus the entire head can be a mass of male and female flowers, although late in the day the balance shifts strongly to persistent stamens as most of the stigmas wither.

Spikelet in early morning. Anthers just peeking forth. Stigmas (white)  are from different flowers in same spikelet.

The species needs a preponderance of anthers as opposed to stigmas, because the roles the anthers have in attracting and feeding pollinators, and in manufacturing massive quantities of pollen.

If functionally male and female flowers can be mixed close together in the same spikelet, does self-pollination occur?   Evidence that effective self-pollination is unusual or nonexistent is that  many flower heads mature no fruits, or very few, while some others are productive.  Fruit productivity reflects luck in cross pollination.  No visitors from other flower heads carrying pollen from afar, no fruits.

If thwarting self-pollination does not seem a  key reason for  protandry in individual flowers, what is the benefit of a flowering making stamens first?   I don’t know, but have a speculative notion:

As the stamens and stigmas mature they have to pass through a narrow bottleneck of tiny leafy bracts in order to see the light of day.  If the soft and delicate stigmas matured first they might be crushed in the bottleneck by the large, firm, pollen-filled anther bullies.   Like letting the mice off of Noah’s Ark before the horses.    Once the anthers have “cleared the door,” it is safe for the more delicate stigmas.

Reported visitors include bees and hoverflies (syrphids), an interesting combo given that both feed on or gather pollen.

 

Torpedo Grass, You Can’t Kill It With Vinegar

Panicum repens

Poaceae, The Grass Family

The names:

Panicum refers to the panicle, a branched, flower cluster.

Repens means creeping.

Torpedo grass is the perfect name.  Not only does the sunken rhizome look like a torpedo, it behaves like one too.

 

The essentially tropical species torpedo grass is of unknown origin, generally but not unanimously regarded as indigenous to the Old World, and invading the Americas at least as far back as the 19^th Century. The grass once served as a forage grass, although it has some livestock toxicity.   I wonder if it is experiencing a northward range extension via global warming. Nowadays torpedo grass is one of the premier weed pests in southern states, and around the tropical world.

The grass is OUTRAGEOUS!   Here are some TG OMGs:

Rhizome pieces can grow to the surface after burial of over 12 inches.

They survive at least 60 days buried.

Living rhizomes have reportedly turned up under soil about 20 feet deep (huh!?) and under 5 feet of water.

Rhizome segments remain viable after at least 10 weeks of floating.

They can dry out and then later sprout.

The torpedo can penetrate wood and asphalt.

Growth can exceed half an inch per day.

A single rhizome node can make 20,000 buds in a year.

Torpedo Grass covers over 16,000 acres around Lake Okeechobee.

Usually associated with wet habitats, the grass can occupy dry sites, even in scrub.

Salty habitats are just fine.

The species is allelopathic, that is, it poisons competitors.

What a grass!,  despite herbicide, fire, and plowing attacks, it blankets countless acres. In some places, especially those under shallow water, much of the year, TG can form acres of “lawn,” yet I can’t maintain a healthy St. Augustine front yard to keep the HOA golf cart spies content.  Proud homeowners keep their lawns lush with fertilizer.   So how can today’s species make a big happy carpet without  added fertilizer?   Well, maybe it has some, not counting whatever nutritional pollutants are in its wet habitat.  Let’s look into TG and nitrogen:

Over the last few days I’ve botanized a multiacre torpedo grass invasion on a severely disturbed wet meadow.   The surface is essentially bare wet sand.  How sand can “fertilize” tons of torpedo grass might seem a mystery, but here’s the thing:  Mixed grass-legume pastures feed livestock sustainably because the legumes “fix” nitrogen by transforming atmospheric nitrogen gas to ammonium, which plants can use directly.  Fixed nitrogen is the fertilizer nutrient needed in by far the highest volumes.  A legume-heavy field is largely self-fertilizing.   The field west of Jupiter is not a monoculture of torpedo grass, but instead is a mix of the grass and a substantial component of legumes:  Indian shyleaf by the ton,  thousands of wild bushbeans, and additional legumes scattered in small quantities, such as sensitive-pea, alyce-clover, cowpea, and danglepod.  Grass plus legumes, almost nothing else.

Torpedo grass stretchin’ out so far and wide.   But wait a moment—all those taller plants are Indian Shyleaf, a nitrogen-fixing legume

That t-grass responds to added nitrogen is demonstrated in published experiments.  You can deduce the same from one clump in my study area…taller than the rest of the torpedo grass, and darker green.  Why?  The happy grass sits atop a big scary ant nest, and no doubt the anty debris and waste is a nitrogen boost.

Clump of torpedo grass taller and greener than its neighbors.  Go look…well, it is on an ant mound.  The non-grass plants visible are legumes bushbean and shyleaf.

If you don’t believe me about the ants, stick your hand in there for ten seconds.

It isn’t all about legumes and ants.  The ability of grasses to thrive in vast quantities without human-added fertilizer is becoming increasingly attributable to symbiotic nitrogen-fixing bacteria, not in nodules, as in legumes.   Instead, nitrogen-fixing bacteria live in the grass’s root zone, or sometimes housed within leaf bases around rhizomes,  or even within the grass tissues.  This area needs a lot of study.   Nitrogen-fixing bacteria have been reported a couple times associated with torpedo grass.

More astounding are additional bacteria associated with the grass and able to neutralize nasty acid soils, extending the already super powers of the torpedo grass into acid environments.

Weirdly, TG seems to be taking over the world despite poor seed production, at least in places.   The species is reportedly unable to make viable seed in large parts of is range, including much of Florida.   A study at Lake Okeechobee where the grass is out of control failed to find viable seeds in the soil seedbank.  Thus most of the Florida reproduction is clonal,  such as by floating rhizome fragments, also by axillary buds produced along the rhizomes.  Just think, in a genetic sense a clone is one individual.  That would mean South Florida is being devoured by an immense immortal botanical amoeba.  Talk about going green!

The rhizome-buds are generally immune to herbicide applications, making torpedo grass hard to control chemically.  Tilling encourages it. Fire can’t touch it.    Weed-killing fungi have been tried but can’t do the job.  We may be SOL.

Long thin rhizomes running hither and thither.

They are hollow gas pipes.

To add to the immorality, the rhizomes come in two different forms, sometimes totaling to over 85% of the plant’s biomass.  One form is long, narrow, and able to penetrate the earth submerged, or to run across the surface of the ground.  The long narrow rhizomes have a hollow center, clearly allowing gas exchange deep in the ground or submerged in water.  These rhizomes put the torpedo in torpedo grass, helping it spread and invade like wildfire. The thin rhizomes can be so abundant to form mats 6 inches thick.

The second rhizome type is thick and gnarly, looking like a ginger “root.”   Those who study the species actually call them “ginger root” rhizomes.   These seem to let the species hunker down, store starch, and maybe sit tight until conditions become right for sending out a new infestation of the long thin rhizomes.   Torpedo grass has been documented to “go dormant” under seasonal floodwaters, then resume spreading as water recede.  Alternatively, the rhizomes can make a floating mat.

Ginger root style rhizome on torpedo grass

To sum it all up, torpedo grass is a species you can’t kill, eager to colonize wet places, standing water, scrub, acid soils,  and probably the surface of Mars.    It is armed and dangerous with aggressive imperial rhizomes and with resting food-storing rhizomes.   You can curse it, and sometimes all we’ve got is resignation.    But then again, a super-weed with crazy growpower ought to be good for something.   Does all’s green make a little contribution to carbon dioxide reduction?   Isn’t it good for some biomass purpose?  Maybe as a bioweapon…dice the rhizomes and spew the pieces on the enemy?

 

Plants and Salt

Floridians live where plants meet salt.  The ocean’s pretty big, and in other regions salty plants hang out inland at saline seeps,  salt licks, salt flats, and even roadsides where salt trucks fight ice.  Salt-loving plants are called halophytes, although how much any halophyte actually “loves” salt is always a reasonable question.   Many salt-“loving” plants grow happily in un-salty cultivation, red mangroves for instance.   Sometimes the “love” for salt may boil down to tolerance, making a salty habitat where a halophyte competes best.  How plants need, prefer, tolerate, or cope with salt varies.  Unrelated species have evolved salty ways in different fashions.   Always fun to explore.

Start with mangroves.  Around here we have red, white, and black, all unrelated to each other, and each with its own mechanisms for dealing with seasalt.  Red mangrove holds down its internal salt concentrations by excluding it at the root.   The gated community approach.  Comparatively low internal salt levels might help red mangroves operate their complex system of pumping air to the roots, allowing growth in deep tidal water and suffocating mud. Just speculating on that.

Salty tissues offer protection from bugs and fungi.  Red mangrove, being the least salty of the local mangrove species, seems to have the most fungally infected and bug-eaten leaves of the trio.

Red mangrove…low salt = high fungal trouble?

Black mangrove handles salt by secreting it onto the leaf.  Much presumably washes away in rain, although a margarita-rim crust on the underside is fairly persistent.   The pass-through salt system may help hold the internal salt levels down.  In our measurements black mangrove was in the middle of the three saltwise, although there would be variation under different conditions.  The salt crust was left in place for the measurements shown below.*

Black Mangrove salt crust on leaf underside

White mangrove can secrete salt from glands on the leaves, which are not those two nectar glands on the leaf stalk.   It does not secrete as much as black mangrove, and in our experience does not become salt-encrusted.  Instead, it has somewhat succulent leaves where salt collects internally.    It had by far the highest salt concentration of the species measured.

Sacrificing entire leaves is costly.  Another way to shed salt is to package it in little bladders,  and then drop or pop them externally.  Waste bags!   Such ability is scattered a little in the coastal plant world, famously in the Amaranth-Chenopod Family, for instance the coastal plant Atriplex, Sea Orach.    Its salt bladders appear mostly on the undersides and margins of young leaves.  They fill and burst, leaving busted bag remnants and salt crud on the underside of the leaf.   As with mangroves, botanists have determined the salty coating to be bug-deterrent.

Atriplex salt bladder, microscope view

White mangrove gave us a hint already of another way to deal with salt:  succulence.   Seaside plants don’t have much freshwater to flush out salts or to cool evaporatively in the hot beach sun.    Succulence gives salt sequestration, protection from temperature spikes, water storage, and maybe even padding from windy beach conditions.  It must be a “good idea,” because seaside succulents abound: Batis, Cakile (sea rocket), Iva (marsh elder),  Salsola, Scaevola (inkberry), Sesuvium (sea purslane), and more.   Go find a beach plant and, if not a grass, odds are it is succulent.

Several grasses thrive in salty places without succulence.  Some have microscopic salt glands on their foliage.   Virginia Dropseed, a beach and dune species, is a photo-example.  Each salt gland is a short two-celled bump surrounded by four taller bumps called papillae.  Do the papillae protect the glands they surround?

Virginia Dropseed grass. Small salt gland (red marker) surrounded by taller papillae, apparent protection for the gland.

 

Gland with papillae

Certain species we do not know as salty sometimes thrive in semi-salty places, becoming a wee bit succulent when hanging with salty friends.  A local example is Virginia Creeper.  Does the Creeper thicken as a result of salt exposure, or alternatively, are the thick-leaved Creepers a separate genetically adapted strain, salty ecotypes?    For those with time and inclination it is easy to distinguish the two possibilities.   Grow them in a common garden.  Depending on the species, you can find either case.  I strongly suspect with Virginia Creeper succulence is acclimation by individual plants…my bet is if you take a normal Creeper and grow it in salt it thickens.   Either way, compatible solutes help…let me explain:

Salt sucks.  It draws freshwater by osmosis.  That is why if I drink sea water the brine in my stomach draws water from my surrounding tissues and dehydrates me.  If you put a freshwater plant in saltwater, it wilts because the salt “sucks” the water out.

It is not just salt that does this, but any dissolved material.    One way a plant can fight water theft by saltwater is to accumulate its own internal “salt” (dissolved material) to win the osmotic tug of war with the outside salinity.   These protective “salts” are called compatible solutes.  A well documented heavy user of compatible solutes is the mangrove associate Golden Leather Fern, Acrostichum aureum.  At different points in its life cycle the fern uses different compatible solutes to keep its tissues just a little “saltier” than the surrounding water. Different levels of salt stress can bring forth increasing levels of compatible solutes.

Watch the wilt.  Two VA Creepers. The one on the left from a mangrove swamp. The one on the right from non-salty “normal” situation.   The two placed in saltwater at the same time and photographed over a few hours.  The one from the mangrove swamp tolerated the saltwater.  The other wilts painfully.  CLICK

——————————————————————————————–

*Five leaves of each species were placed in the same volume of tapwater in a blender.
Zero” on the graphs was the level of saltiness measured in a cocoplum grown away from salt.   The units siemens/m reflect electrical conductivity.

 

Sunburned Tops, Soggy Feet

Aquatic Emergent Plants

South Florida is rich in plants growing with their roots submerged at least part of the year, and their tops periscopes above water.   Many unrelated plants have evolved this lifestyle separately.   The convergences and divergences in unrelated species united under one extreme lifestyle makes it all intriguing. And they range the spectrum from fundamentally landlubbers able to withstand temporary flooding to floaters able to withstand temporary stranding.

Pickerel weed emergent. By John Bradford.

Emergents come from all corners of the plant world, including ferns and fern allies (Isoetes) to flowering plants from numerous families.   Monocots rule the marsh, with such representaives as arrow arums, arrowheads, cattails, golden clubs, grasses, pickerel weeds, rushes, sedges, and more.

Many emergents imperialize large spaces by subterranean rhizome growth.    You might say with limitless sun and usually unlimited water, two arenas for competition might be nutrients and space.   Some marshes house carpets of a single species, or multiple carpets of multiple species pushin’ and shovin’.  Sometimes competing species intermix, sometimes they occupy pure stands.

Sagittaria graminea by John Bradford.

Sunken rhizomes are useful beyond colonization.  Water levels fluctuate seasonally.  Emergents may spend months high and dry where risks include drying, sun, fire, grazing…or the other extreme, flooding.

Hey—where did the water go?

Apocalyptics like underground refuge.  Some species double down to face dryageddon by making thick starch-storing rhizomes, or tubers such as water chestnuts, chufa, and sagittaria (aka “duck potato”).  We’re ready, come hell or high water!

This photo shows subterranean “be ready” starch storage in Sagittaria.  The dark stained area in the rhizome shows starch storage.  Starch reserves stop abruptly at the leaf bases.

Sagittaria rhizome sliced to show starch storage.  The starch is stained with purple.

Emergent usually have ductwork called aerenchyma (air-EN-cah mah).   If your feet are under oxygen-starved mud and your top is above water, ventilation shafts help,  “air” channels from leaves to roots. The snorkel analogy is too simplistic, however.   The pipes are not generally open to the outside air.   They usually are more or less closed, sometimes pressurized. Let me explain:

The leaves make oxygen as a waste gas, and require carbon dioxide to make sugar.   The submerged roots do the opposite…they use oxygen for respiration while shedding carbon dioxide.  They make what the leaves need and take in what the leaves shed.   And the reverse prevails up in the leaves.  So it makes sense for  the leaves and roots to trade gases.   A closed pipe system allows the leaves and roots to decontaminate and feed each other…oxygen moving down where needed and carbon dioxide moving up where needed.  Too much outside venting may interfere with such self-contained exchange.

Sagittaria leaf stalk cut lengthwise to show air channels.

Sagitaria leaf stalk cut across to show air channels.

A plant physiologist studying cattail found the carbon dioxide concentration in the aerenchyma to be 10 times the atmospheric concentration. To the foliage that’s a photosynthesis supercharger.   John and I measured carbon dioxide released from cut aerenchyma at the base of a sagittaria.   The technique would necessarily under-estimate the concentration, yet our reading rose to 5683 parts per million,  even higher than the 10-fold increase in cattail, given that the atmospheric carbon dioxide concentration is a bit over 400 parts per million.

Okay then, does the leaf aerenchyma pipe oxygen rootward?   We cut off several leaves and inserted their stalks (petioles) into a sealed test chamber with an oxygen sensor. The atmospheric oxygen level outside the chamber as 208,284 parts per million in contrast with  224,389 inside.      Yes, oxygen from the leaf photosynthesis is clearly southbound down the leafstalk air channels.

The species we tested Sagittaria lancifolia has thick leathery leaves you might expect on a desert plant or on a high dry epiphyte, not where water seems unlimited.

Emergents often resemble plants of arid circumstances.   Many have thick resistant blades, or nearly leafless photosynthetic stems, or pencil-shaped leaves with minimal surface area.    Easy to explain at a “hunch” level:  ready for seasonal dry times, robust to relentless marshland sun,   and perhaps root- impaired by suffocation in standing water and waterlogged mud.

The Everglades marsh ecosystem under natural conditions was famously nutrient-limited, most notably phosphorus.   Modern pollution high in phosphorus and other nutrients disrupts the natural species balance.

To turn to the other end of the nutrient spectrum, marshes gobble up unwelcome nitrogen, phosphorus, and other nutrients from sewage effluent.  Visit such water treatment sites as Wakodahatchee or Green Cay wetlands, and see the nutrient-loving species composition of hyper-enriched waters.  Broadleaf arrowhead abounds, true to its reputation as a nutrient vacuum.

Nutrient-loving aquatic species at Wakodahatchee Wetlands.