Bladderworts High and Dry Where Bladders Don’t Belong

Utricularia cornuta

(A utricle is a bladder. Cornuta means horned, referring to the spur on the flower.)

Lentibulariaceae

Horned Bladderwort by John Bradford.

Many wildflower enthusiasts are familiar with Bladderworts, species of Utricularia.    Utricularias are generally thought of as aquatic carnivorous plants dangling microscopic suction traps in the water.  The traps have trigger hairs and a trap door. When a minute swimming arthropod bumps the trigger, the trap sucks the victim in for lunch. That is documented richly on the Internet so no need for more here.

What has been interesting me this week is Utricularia growing in moist sand, often by the thousands in drifts of yellow.    Any questions? Question 1:  What pollinates a hundred thousand bright yellow blossoms all glorious at once in a couple acres?  That’s a blog for another day.

Question two is the topic for today:  How can an aquatic water-filled bladder catch water-borne prey while stuck in sand?  There has to be more to the story. There is, some of it well known, some mysterious.   As the pundits say, “let’s unpack it.”

First of all, don’t the plants root in the sand? No—Utricularia has no roots, although we will soon see leaf-ish structures functioning much like roots.

But let’s stay above ground a moment.   Plants typically need to photosynthesize, and that is a job for leaves.  But where are the photosynthetic leaves?  The plants look like a bare stalk with a flower out of focus on top.

Vertical pins rise from the leafy mesh below the surface.

Just below the soil surface stringy leafy segments form a horizontal mesh, think of a smashed plate of spaghetti.  From that mesh millions of pin-sized segments rise vertically from the soil into the light of day.  The collective surface area of countless pins is substantial, like the microvilli in an intestine. They are green or partly red (sunscreen? damage?) and probably allow for photosynthesis, and conceivably help aerate the leafy portions below the surface, especially during flooding.    Room for research here!

A growing literature is revealing the idea of the trap feeding the plant by catching and digesting prey as simplistic.   The traps seem to be micro-ecosystems unto themselves.  CLICK

Trap-dwellers include microscopic protists, such as ciliates, bacteria, fungi, algae, and so-called bluegreen “algae.” Bluegreen “algae” are photosynthetic cyanobacteria often able to “fix nitrogen,” that is, convert atmospheric nitrogen to fertilizer.

The microbes manufacture nitrogen fertilizer inside the trap, you say?   Isn’t the main point of the carnivorous plant to obtain nitrogen from breaking down the insect victims? And photosynthetic bacteria inside the trap provide the same benefit without bloodshed?   Yes, if not studied adequately yet.

OK then, nitrogen-fixing cyanobacteria live inside the trap, possibly contributing to the plant’s nitrogen nutrition, what about outside the trap?   Not a new idea.  Botanists have recorded cyanobacteria clinging to the outsides of traps in the water.

So now think about that comparatively dry meadow of sand-dwelling utricularias.   Could  cyanobacteria in the sand be enriching the soil, maybe replacing the need for aquatic bug-catchery?

A close look at a population of Utricularia on “dry” land shows them mostly to rise from a thin surface carpet of periphyton, although not always, and there’s more to the picture.  Under the Utricularia is a blue-green living layer a fraction of an inch under the ground surface.   It looks like a miniature seam of coal.

A living blue-green seam in the soil

With room for more data (!), I suspect the land-living Utricularia is deriving nitrogen and possibly additional nutrition from the subsurface blue-green layer.  A look at that layer with a microscope shows it to consist in large part of, you guessed it, cyanobacteria.

Cyanobacteria from the blue-green layer at the base of a Utricularia.

The plants form a thick brushlike mass  of rootlike leaves usually just below the green layer, or sometimes branching directly into it too.   The false roots can have traps, which exist to absorb nitrogen.   But who said it has to come from within?  Traps bathed in nitrogen fixed by a living soil layer of Cyanobacteria might as well absorb it from the outside as well.

 

 

Purple Bladderwort Has Aquaponics

Utricularia purpurea

(A utricle is a sac.)

Lentibulariaceae

Brightening shallow waters and wet muds round town right now are intricate carnivorous plants, the bladderworts, in some places thousands of them.   Several Utricularia species make Palm Beach County a better place, all of them showy yellow-flowered, except one,  purple bladderwort having, duh, purple flowers.

PBW by John Bradford.

We’ll get acquainted, but first a word about bladderworts in general.   They typically have finely divided stringy leaves and live in shallow water or in wet mud.  Flowerless you could mistake them for algae.  Look closer though, on the foliage are tiny (let’s say 1 mm across) bladders, little slurp-traps with a trap door and trigger hairs.  Tiny creatures swimming by trigger the triggers, and SNAP,  the trap springs open like the wicked witch’s oven, and the small passerby becomes lunch.

Death traps magnified, with clinging brown detritus.

Utricuaria purpurea is one of over 200 worldwide species of bladderworts, and its astounding distribution extends from Central America to somewhere along Hudson Bay.   It takes the cold bravely via tiny tubers called turions hiding safely in the lake bottom mud.   In our area the foliage masses can be the size of a garbage can, often looking brown.

Foliage with traps.

The inconsistent tendency toward brown is not a sign of morbidity.   Under the microscope even brown leaves sustain healthy chloroplasts.    The brown seems to be largely material clinging to the foliage, including dead and living algae,  mixed detritus, diatoms, fungi, cyanobacteria, and who knows what.  No doubt the mix depends largely on the site.

The flower by John Bradford.

Now back to those fearsome traps.    Utricularia purpurea is one of the species calling the role of the traps into question.     Today’s speculations are not necessarily mine, as other observers have given this matter study and thought.

First of all, a study in one place and time is a snapshot,  and just like a snapshot on Facebook, it is inadequate to assess the big picture.   That said, there are reasons to suspect that, “catch a bug and eat it” is not the whole truth and nothing but the truth, even though the traps contain glands producing digestive enzymes.   But there’s more to it:    First of all, the plants invest substantial resources in making those traps, which, however, often appear under-rewarded with the expected victims (but not always).   Secondly, the plants secrete carbon compounds into the trap fluid, as though they are feeding something.   Third, the traps contain a lot of healthy squirming life other than dying victims.   The traps are home to micro-ecosystems of bacteria, sometimes cyanobacteria, apparently healthy protists, and some small multicellular varmints.  Below is a short movie made today of residents in the traps.  Check it out:

CLICK HERE to see life in the trap.

Which are victims?   Which are exploiters or predators?   Which are bycatch?  Which have a mutually beneficial relationship with the plant? Which are in multiple roles?

In the last-mentioned case, biologists plausibly wonder if the plant is feeding its trap colony food from photosynthesis (those carbon compounds) and receiving in exchange nitrogen and or phosphorus waste from those within.    What a great area for research.

You may be asking, if the trap has all those tiny inhabitants, how do they get in?   It turns out even minute stimuli can say, “open sesame,” and the traps can open and close repeatedly, even in a short time.  I’ll bet I know how they all get out…ultimately as fertilizer.  In short, perhaps instead of merely being trappers, bladderworts invented microscopic aquaponics.

 

—————————————————————————

For those who want to dig deeper:

https://www.jstor.org/stable/2657137?seq=1#page_scan_tab_contents

https://academic.oup.com/jxb/article/61/1/99/567342

 

 

Bladderworts and Other Bugivores

Drosera capillaris   Droseraceae

Horned Bladderwort (by JB)

Today John and George  explored  a small pond and adjacent Bald Cypress swamp margin in Jonathan Dickinson State Park near Hobe Sound in preparation for an upcoming educational event.   Carnivorous plants ruled today, so here we go on Bladderworts n’ stuff.   We scored a  Utricularia hat trick, encountered three different species all in flower in a small area.  Generally called Bladderworts,  the  genus contains 214 species altogether.

Zig-Zag Bladderwort (by JB)

Flesh-eating plants represent diverse plant families of Monocots and Dicots, and are not closely related to each other.   They have evolved in situations where the main plant nutrient, nitrogen in its various forms, is in short supply,  or where impaired root functions make it hard to take up, or where roots are absent altogether,  as in Utricularia. Insectivory  captures nitrogen in sterile sandy soils, in acid substrates, on epiphytic perches, in anoxic muds, and sometimes in aquatic habitats.  Utricularias look more like Algae than Flowering Plants—until you spot the beautiful flowers.

Genlisea with trap (Google Images)

The Genlisea traps are tubes, topped with two weird  long twisted appendages at the open end.   They look a little like those blow-up arm-flapping tube men they use to draw attention to used car lots and furniture sales.  The armlike appendages have inward pointing hairs.   Varmints swim in but can’t back out, because the hairs are a unidirectional valve,  as some fish traps catch fish.  The Genlisea traps are technically rolled leaves, so it is possible they evolved from simpler ancestors having in-curled blades resembling those of Pinguicula, making Genlisea sort of a “missing link” between simple Pinguicula and the complex traps in  Utricularia.   Perhaps relevant to this, Genlisea species have foliage leaves in rosettes  resembling those of Pinguicula.

Bladderwort bladder with trigger hairs (Photo by Jose Almodovar)

Utricularia traps are bladder-shaped or look like one of those goatskin wine squirt bottles favored by skiers.    The door leading into the bladder has a trap door.  Near the trap door are microscopic trigger hairs.  When the victim jostles the triggers,  the trap door releases and the bladder expands rapidly, sucking in the meal, as a slurp gun sucks in an aquarium fish. The in-slurp happens in a tiny fraction of a second.

CLICK for video

Today’s three Utricularia species are a study of variation within a single genus.   Leafy  Bladderwort  (U. foliosa) lives suspended gracefully in the standing water,  looking at first glance like a green alga waving in the pond.   It builds up huge slippery biomass.   Oddly, the species is distributed in the Americas and in Africa.

Leafy Bladderwort in water (by JB)

The other two, Zig-Zag  Bladderwort (U. subulata) and Horned Bladderwort (U. cornuta), inhabit  moist muds.   They both have fine threadlike leaves hidden in the soil.    They differ in their flower structures:  living up to its name (cornuta = horned), Horned Bladderwort has a long horn-shaped spur on the flower.   Zig-Zag Bladderwort is one of several species in ur area capable of making cleistogamus flowers: tiny flowers that self-pollinate (or somehow develop seed) and never open.

This species has a second quirk.  Where are the photosynthetic leaves?  It has some leaves but not much.  Botanist Wilhelm Barthlott and collaborators, citing earlier research, discuss this species as one of the few “carnivorous” plants that derives energy and not merely minerals from carnivory.

Around our feet, the Bladderworts had competition for the buggy menu.  The wet ground was littered with beautiful tiny Sundews (Drosera capillaris).  The reddish leaves on these are shaped like spoons and are covered topside with long hairs, each hair with a glistening glandular tip.   Insects who touch the tarbaby get in worse and worse as they struggle, until the goo-tipped hairs bend inward and press the corpses to the digestive leaf surface.

Sundew enjoying lunch (Photo by JB)