Red Mangroves Catching a Few Rays

Rhizophora mangle

(Rhizophora means root-bearing.  Mangle means mangrove in Caribbean  Spanish.)

Rhizophoraceae

 

Continued play in the Peck Lake mangroves near Hobe Sound, Florida, this morning kept John and me as happy as dogs with two tails.   We’re trying to figure out what makes mangroves tick.

Red Mangrove y John Bradford

Start with the embryos.  All our local mangrove embryos germinate precociously, with those of White Mangrove sprouting within the fruit, those of Black Mangrove dropping from the fruit.  CLICK for Black Mangrove.  In Red Mangrove the embryo grows several inches before dropping, leaving its top parts behind.

By JB

How the mangroves handle salt varies.  Black Mangrove secretes it abundantly from leaf pores.  White Mangrove has such pores,  but seems more prone to stash salt in expendable foliage.   Red Mangrove emphasizes blocking salt at the roots, leaving the leaves free to specialize on air circulation.  On that topic, White Mangrove tends to have the least-oxygen-starved roots, and can send specialized snorkel pegs upward as needed to get above suffocation.   Black Mangrove extends its little “dead man’s fingers” vertically above the anoxic ooze. These need more attention but not now.

Red Mangrove is the star today, and its aeration system is extreme.  Of our three local contenders Red is most tolerant of tidal submersion and thus may need the most aggressive air circulation. Sources like to say the species services its sunken roots by allowing air into its big prop roots arching above the water level.  Makes sense…the submerged roots need air and the prop roots rise into the air just above.  Any defense attorney can tell us not everything that makes sense is true.   Research by a couple generations of physiologists reveals a more complex system.

Stilt roots, by JB

A Red Mangrove recognition tip I mention in my native plants class is freckles on the undersides of the leaves, dozens of dark pinpricks.   They are not salt glands.  Instead, they are air-intake valves called cork warts.  The cork warts penetrate into the leaf like little thimbles, broad at the leaf undersurface and narrowed upward far into the leaf, ending adjacent to open air-conducting tissue near the top leaf surface.

Cork wart freckles by JB

Dark cork warts mixed with countless green stomates.  When the stomates inflate and open does that impinge on the cork warts?  Just  a hunch!

That leaf airspace is connected to ductwork leading all the way down from leaf tip to submerged root tip.  That long-distance HVAC system must need pressure.   Pressurized air is known in wetland plants, and has surfaced previously in the blog.  The solar-powered air-blower resides in the leaf blade’s air spaces, the sun-generated heat pushing the air out of the leaf and down down down through a system of air-conducting tissues.   The old air escapes from the roots, either below the waterline or above, the exit strategy needing research. Some botanists think the released air helps oxygenate the stinky mangrove mud.

You might ask why the pressurized air flows cooperatively down though the ductwork rather than leaking back out the cork wart entry points.  That can happen, as shown experimentally with hyper-pressured leaves held underwater bubbling from the cork warts.  Even if there is some naughty backflow, air goes down the plant too.   Rising pressure may alter the shape and structure of the cork warts to impede backflow.   Additionally, the air can enter the leaf 24/7 and seep deep into air spaces getting far from the potential exits before sunny times generate pressure.  Conceivably millions of stomates open and turgid during the sunny day may force the cork wart valves closed.   On top of all else, warmer air flows toward cooler air in Knudsen Pressure.    Most of this paragraph is speculative, but in any case forced air starts in the leaves and exits the roots.

For a pressure test John and I connected a delicate pressure gauge to a couple leafy Red Mangrove twigs, and to non-mangrove leaves and leafy twigs, and monitored pressure changes over time during changing light conditions.   In non-mangroves the leaves generated a negative pressure, suction, as water is pulled up and out via evaporation from the leaf blades.  The pressure decreases over time.  Non-mangrove leaves are suckers.

Blue line = solar radiation at the leaves.  Dark green line = air pressure  coming down twig from leaf cluster.   As the sunshine increases so does the pressure.   When sunshine dips, so does pressure. The two are tightly linked.

Here is another—different branch, later in day, same pattern:

The jagged brightness line is due to passing clouds.

In Red Mangrove, by contrast, when and only when the sun is bright the net effect is positive pressure. Sunny  Red Mangrove leaves are blowers.   But, as the graphs above show, only when the sun is bright, the pressures being highly attuned to sunbeams vs. cloudy skies.

More speculation.  If bright sun on the leaf surface pumps air to the roots, does the parabolic arrangement of the leaves at the branch tips help absorb the air-pumping solar radiation like a parabolic antenna collects radio waves?

Parabolic solar-ray catcher?  The pressure readings in the graphs above came from a point essentially identical to where the twig crosses the bottom edge of the photo left of center.

 

Baldwin’s Milkwort – Gotcha!

Polygala balduinii

(Polygala means much milk, from the belief that these plants promote lactation. William Baldwin was a physician and botanist active in Florida and in other states.)

Polygalaceae

Today John and I continued to fuss and fume over mangroves and soil salinity in Hobe Sound.  Adding to the experience, at this moment in flower all about the wet meadows are pretty and smelly Baldwin’s Milkwort.   Smelly because the plants upon bruising perfume the air with essence of wintergreen.

Polygala balduinii by John Bradford

Wintergreen oil is methyl salicylate.   We buy the stuff to relieve discomforts, such as by rubbing it on the skin.  Big surprise…chemically the oil is essentially aspirin, likewise a derivative of salicylate, aka salicylic acid.   The methyl salicylate is bound in the intact plant to sugar, and in that condition remains in odorless reserve, until physical injury unleashes an enzyme able to separate the wintergreen from the sugar, setting the fragrance free.

Salicylic acid is not merely a human pain reliever, it is also an air-borne hormone alerting the rest of the plant to prepare its “immune system”  for attack.  Not sure, but probably that’s what the wintergreen fragrance release upon injury is all about. Wintergreen and Polygala are not the only plants to bear methyl salicylate.   Here is the state of the art in 1898:

The Polygala balduinii today was so pretty, having heads of bright white flowers, each with a tiny yellow center,  we had to wonder what pollinates it.   No answers on Google.

By JB

 

We hung around awhile to try to spot pollinator action.  Although we saw no pollinators, we did encounter somebody else likewise waiting for a floral visitor…an Ambush Bug loitering among the flower heads.

Ambush Bugs live up to their name, waiting among the attractive flowers to waylay an innocent pollinator who comes a’visiting.    These ambitious little ner-do-wells grab prey vastly larger than themselves, including honeybees, small butterflies, and roosters.

 

White Mangrove and Its Multifarious Roots

Laguncularia racemosa

(Laguncularia comes from Latin for a small bottle, in reference to the fruit.  A raceme is a type of branched flower cluster.)

Combretaceae

This morning John and I probed the saline mud around Peck Lake, near Pt. Salerno, Florida, attempting to discern a relationship between the flora and the increasing salinity levels approaching the shore of saltwater Peck Lake.    One thing I learned is that 66 11/12 is too old for scrambling over the handrail and down off of boardwalks to get personal with crabs in the mud below.  A good place though to think about the many adaptations Mangroves have to their smelly salt life.

White Mangrove by John Bradford.

Before we go on, let it be clarified that the word “Mangrove” refers to a tropical tidal swampy muddy briney lifestyle.  The many mangroves of the world are not related to each other, and the club has indefinite inclusion, where two honest observers may disagree as to whether a given species is a “mangrove” or not.

Today’s White Mangrove is more closely related to Tropical-Almond, Black-Olive, the vine Rangoon Creeper, and Buttonwood than it is to Red or Black Mangrove.    That mangroves are a result of convergent evolution is what makes them so interesting…the different ways disparate salt-swamp coastal species solve the same problems.    For instance, Red Mangroves block salt entry instead of dealing with it internally.  Reds reportedly have the lowest salt tolerance of the local Mangroves despite usually being the one with the wettest feet in the seawater.  Black and White Mangroves, by contrast, allow salt to enter the root and rise throughout the plant.

Both White and Black have tiny glands on the leaf surfaces able to pump out the brine. Yet there’s a difference.  Black Mangrove obviously dumps a lot of salt.  Its blades are usually white-crusty, and taste like a pretzel.   But White Mangrove foliage seldom has such crystal crust.  Excretion doesn’t seem to be as important to this species.   White sequesters salt in its thickened fleshy leaves, periodically discarding and replacing them.

Below is a quick and dirty demo. The first cup contains only tapwater, reading 44 salinity units (mS/cm), reflecting the fact that tapwater does contain salt, defined broadly.  Toss in 5 sliced White Mangrove leaves, wait a few ticks for salt to dissolve into the tapwater, and the salinity reading climbs in the second photo.

Tapwater with salinity measured (as EC in mS/cm).

Same water with White Mangrove leaves giving up their salt. Note increased reading from 44 to 58.

Salt glands are not the only curiosities on White Mangrove leaves.  Near the margin is a line of tiny black cavities.  These domatia are barracks for microscopic symbiotic mites.   The related Buttonwood has them as well.    On the leaf stalk (petiole) are two raised glands often misinterpreted as “salt glands.”  No…the real salt glands are microscopic, whereas those two petiole bumps are sugar fountains for symbiotic ants, in the right times and places.

Nectaries on WM petiole, by JB. The tiny smaller glands are visible scattered lower, on the leaf blade.

The most interesting parts are the roots.    First a little context.   Mangroves live in water or in tidal muds suffocating to unspecialized roots, so the Mangroves each have different coping specialties.   Red has famous prop root flying buttresses arching out from the trunk above the water.    Black has spooky vertical “dead man’s fingers” pointing heavenward  from buried horizontal roots.   White has an intricate root aeration system, which is hard to spot.

White Mangrove roots are shy, often submerged or nearly so in water or mud.  The system  entails at least four different root types, as displayed in the following 1970 diagram by botanist Jan Jenik (linked below):

Cable roots horizontal at base.  Vertical pegs rise from these, with small feeder roots along the pegs.  Clusters of little snorkels (pneumathodes) rise from the enlarged tips of the pegs.

Starting at the deepest, large thick White Mangrove roots run horizontally under the mud.   From these rise vertical medium-peg roots to a little below or a little above the water or mud.   These often have slightly swollen heads.  To the pegs are attached the thin feeder roots. What a perfect place to be a feeder root, since as the water and oxygen levels rise and fall the positions of the feeder roots probably rise and fall  by means of death and regeneration correspondingly on the pegs.

From Jenik, see text.

All those feeder roots need aeration.  For this purpose on the peg tips arise stubby, thick, short-lived chimneys (pneumathodes), venting air through a soft porous outer layer all the way to those needy feeder roots.

 

Pegs with pneumathodes today.

Outer layer of pneumathode is spongy.

Pneumathode has big white breathing pores (lenticels).

——————————————————————————————————

[Forgive a non sequitur.  Part of the reason Bald Cypress knees do not seem to be root-zone air vents is that they are nowhere near the active feeder roots..]

Jenik article:

http://www.preslia.cz/archive/Preslia_42_1970_105-113.pdf

 

Livin’ Funky Below the Lichen Line

Syrrhopodon texanus and friends

(Syrrhpodon comes for Greek for crowded teeth, in reference to the spore release mechanism)

John and I worked today in Peck Lake near Pt. Salerno, Florida,   with lichens on mangroves, although for blog purposes I’m broadening to a nearby bald cypress swamp.   Lichens thrive almost anywhere, on trees, on rocks, on tortoises, but they do have secret loathings.  As covered last week, many dislike pollution.  Submersion is worse.  Baptism can set them back.  Observers in New Orleans CLICK can still pinpoint the peak water levels from Katrina marked by the “lichen line,” the trees there hosting healthy lichens above the line, and few (or after 15 years, different species) below it.

Lichen lines are divisive in PB County too, on bald cypresses where the water can rise and drop multiple feet per year.   Walk in a dry bald cypress swamp today and the lichen line is at your knees or above, equal on each trunk.

You don’t see many sharper borders in nature, two ecosystems separated by inches.  Above the border a dozen multicolored lichens along with tillandsias, ferns, mosses, and more.

Below it, however, bang, a completely different flora tested by the crucible of submersion half the year, high and dry the other half.  Who can withstand such eco-whiplash?  Does submersion eliminate all lichens?  Very nearly.

The lichen Leptogium crenatellum can un-drown happily, although we did not see it today.  Its “algal” component is no alga, but rather a cyanobacterium of the indestructible genus Nostoc.  Nostoc CLICK is responsible for dark jelly patches rising from soggy ground.  Leptogiums thus are called jelly lichens.  They fear no flood.  /

The main plants south of the border are mosses and liverworts, conceivably “pre-adapted” to flooding.  They belong to the group of plants, Bryophytes, most related to algae, which Bryophytes resemble by having every cell in direct contact with the water or air, exchanging gases, nutrients, and wastes like an alga in a pond.  No surprise that some mosses are fully aquatic plants, especially in the family Fontinaliaceae.   Members of this family turn up in bald cypress swamps, happy in the soup, but impaired during the high and dry times.  The dominant below-the-line Bryophytes tolerate both extremes.

Around today’s swamp the dominant moss down low is Syrropodon texanus, one tough customer.   Syrrhopodon stands up to its hard knock submerged-exposed life with reinforced leaves that when dry twist into a protective thatch roof.  Its leaf bases have big clear hollow cells called hyaline cells.  These are “canteens” the moss fills when wet, and presumably consumes slowly as needed later.

Syrrhopodon hyaline cells at leaf base microscope view  The hyaline cells are the clear water bottles between the bands of living green leaf cells.

Another moss below the line, and in many other places, is Leucobryum albidum which has more hyaline cells than green cells.  The plant is a living water tank, the glassy empty cells giving  the leaves a white color.

Leucobryum is white, made 90 percent of hyaline cells.

Moss sex requires “rainsplash” to bounce the sperms to the eggs on the tips of the tiny plants.   That is impractical when underwater half the time and  clinging to an exposed tree trunk the other half.    All three of the mosses listed below each have different methods of sidestepping sexual dysfunctionality by cloning themselves using microscopic breakaway bobbers able to drift to new moorings during the floaty moths:

Leucobryum albidum suffers a reported shortage of male plants, but no problem,  no boys needed, it clones via tiny breakaway cell clumps produced on short stems.  Additionally, its detached leaves can root.

Syrrhopodon texaus disperses itsy bits produced by the thousands on the leaf tips.

Syrrhopodon leaves dry and twisted, with micro-bobbers releasing from the tips.  Microscope view.

Brachymenium macrocarpum has hairlike “rhizoids” along its stem.  The rhizoids spawn microscopic “tubers” to float the species to a new tree.

Rhizoid tuber microscope view, on Brachymenium.

To sum it up, if you want to live as a submarine part of the year it helps to be related to algae, to have built-in water tanks, and to disperse clonally with floaty pieces.

————————————————————-

Liverwort from down below. Microscope view.

 

Dominant  lichens above the line in a Florida swamp:

Chiodecton montagnei

Cryptothecia rubrocincta

Heterodermia albicans

Physcia crispa

Do the mosses, liverworts, and cyanobacteria contribute oxygen to life below the lichen line? CLICK

 

DYCs (revisited)

Posting a day earlier than usual due to some schedule complications.   Today my Pam Beach State College native plants class fanned out to conduct a flowery study in Riverbend Park in Jupiter, Florida.  While waiting for the students to all-ee all-ee in come  free, I wandered through lovely moist meadow and counted the DYCs.

Coreopsis by John Bradford.

DYC is a technical botanical term, standing for Darned Yellow Composites, first-muttered by somebody trying to identify them.   A Composite is a member of the Composite Family,  the Asteraceae,  with some 24,000 species one of the “big 3” families:  Composites, Orchids, and Legumes.   Everybody knows Composites, such as Dandelions, Marigolds,  Sunflowers, and so many more.  Note my cherry-picked examples—yellow.    Not all 24 K Composites are yellow, of course, but I think it fair to say most are.

Deviations from the prevalent yellowness are interesting in their own right, for examples botanists in the Middle East noting a split between non-thorny yellow Composites, and thorny ones of other colors.   Think for example, of purple spiny thistles.   Their contention was that being not-yellow was perhaps warning coloration to flag off herbivores.  Now nobody is saying all non-yellow Composites are prickly, but merely that the family is perfectly capable of being non-yellow if that is the adaptive optimum.   For the moment, let’s think about the many many many yellow members of the Aster Family.   Why should yellow be the main color of a huge family?

Helenium by JB

A boring answer may be, well, they started out that way, their great ancestor had yellow flowers, and the family diversified with the original yellowness deep in the DNA.  Okay sure, but I’ll bet there’s more to it.   Equally boring, you might wonder if yellow pigments are “cheap” to make, or if they tie in secondarily with some underlying metabolic machinery.   Yea maybe, but let’s assume that yellowness is adaptive in its own right.  That it has to do with insect pollinators.  If so, what is so great about yellow flowers in this family with respect to floral visitors?

Hold on, it is not strictly a “family” affair.   Asteraceae are predominantly plants of meadows, fields, and open sunny places.  Come to think of it, a lot of meadow-ish and open-area  flowers are yellow, such as members of the Mustard Family, yellow Poppies, many water lilies,   buttercups, and more.    Maybe there is something beneficial about yellow in meadows, fields, and similar habitats.

Does it have to do with a particular pollinator type?   In a moist meadow in Riverbend Park were most of the flowers today yellow because, say, yellow-lovin’ bees rule?  Probably not.  An idea that is not original with me is the opposite, sort of like politics or marketing.  How do you get the most votes or customers?  Appeal to the broadest audience you can.   Maybe a meadow is no place to be a one-pollinator specialist.   Maybe in the middle of the field where thousands of flowers compete and yet at the same time draw massive numbers of insects, the best approach is to generalize and attract the greatest number of pollinators of whatever sort may be willing to visit.  Wal-Mart vs. Rodeo Drive.

Butterweed,  along Hillsboro River near Tampa this week.

The flower head in the Composite Family is an open plate or bowl anybuggy can visit.   The nectar is easily accessed near the floor of the bowl.   The head pushes the pollen to the surface of the bowl where any visitor can gather it “purposefully,” or merely be dusted with it inadvertently.  The pollen-receiving stigmas rise into the bowl where all visitors, perhaps dusted with pollen, tread and deposit pollen.      The head welcomes all comers, and they all come.   It might be intuitive to think first of honeybees, but in a Jupiter, Florida, meadow honeybees are not indigenous, although other types of bees are.   Beyond the bees, important DYC pollinators include flies, beetles, butterflies, and no doubt more.

Insects see UV, which I  do not.  All those insect visitors are seeing markings in those flower heads we’re scarcely aware of.    Pollen itself is yellowish, so a yellow flower in a sense may send an advertising signal of “woo hoo … pollen here!”    Yellow markings are often associated with flowers specialized for bees.

Casting the net beyond bees,  botanist Sara Reverte and collaborators in 2016 published a survey of pollinator-group color preferences embracing many thousand plant species in different geographic regions.   The following insect groups had yellow as their “favorite” color in at least one region:   ants, wasps, beetles, flies, and lepidopterans (butterflies and their kin).   Yellow might not be “the” best color to draw a single specialized pollinator (not many specialized orchids have yellow flowers), but  if getting the most 6-leggers into your bowl is the goal,  yellow seems a great way to build a coalition.

 

Liken’ Lichens

This morning John and George pondered the ways of lichens in Halpatioke Park in Stuart, Florida.   There’s always much to learn and say about these biological  curiosities.  First we’ll knock off the “Botany 101” basic lichen facts you could find all over the internet, then attempt something more off the beaten path.

A branched “fruticose” lichen, by John Bradford.

LICHENS 101

• A lichen is a symbiotic union between a fungus and one or more algae species, or sometimes cyanobacteria, living together as one.
• Lichens are not all related to each other. They evolved many times.
• Lichens favor extreme habitats such as rocks, concrete, sand, and especially tree bark.
• Lichens, when dry, go into suspended animation, and come to life when moist.
• Lichens exhibit three different body forms:  one form resembles paint, one form resembles a crinkled leaf or fried bacon, and the third form is branched and shrubby.  They sell the last-mentioned as shrubs for model railroads and dollhouses.
• Because lichens are two-species species, their reproduction is a coordination problem.  Most lichen reproduction is thought to be tiny clonal fragments where the fungus and alga elope together, although the fungi sometimes form spore-making organs.
• Lichens come in beautiful colors stolen and applied as lichen fabric dyes.
• Some lichens suppress surrounding competing vegetation.

By JB

Okay then we’ve got the lichen picture.  Now for the weirder parts:

Weird thing 1.  Most lichens grow as irregular shapes, or shields, or roundish patches.   They grow in ways consistent with starting from a point and growing outward like ripples on a pond although far more irregular.  But  today John and I noticed something very different:  a tendency for multiple different types of lichens to appear as horizontal bands, partial belts,  across the oak tree trunks, especially laurel oaks.

Lichens often appear as horizontal band aids.

The way that comes about may be sort of obvious but then again, not.   The obvious part is knowing that the tree trunk expands in girth like my waistline after too many donuts.   It stretches horizontally but not vertically.   If you put a roundish paint spot on a tree and let it grow 10 years the dot will be stretched laterally into a horizontal bandaid.  Strtching ought to make it fragmented and thein.     If two kids take a ball of taffee and pull, it will of course get longer and thinner, or may break.  So here is the surprise…when a thickening tree taffee-stretches a lichen laterally,  it usually does not thin or fragment, even if stretched many times its original diameter.  The stretched part seems to self-heal and re-thicken, even filling in the cracks if fragmentation is apparent.   It compensates for the stretching, you might say adapted to its preordained strain.   If you’re going to dwell on a tree trunk, get ready to be stretched.  You don’t see such banded lichens on concrete, or on palm trunks,  which have minimal expansion in girth.

BY JB

Weird thing 2 is the extreme sensitivity of lichens to air pollution.  There they sit on a tree with no roots and no protection, exposed to every breeze and absorbing every drop of mist and rain,  as well as everything carried in that wind, mist, and rain, including nutrients,  radioactivity, and toxic pollutants.   That tendency favors some lichens, for example, if the air pollution is rich in nitrogen compounds, certain lichens may say, “thank you for the free fertilizer.”   Most often though, it seems to me, air pollution diminishes lichen coverage and diversity.   The most obvious sources of air pollution around here are highways, and the pollution-effect was apparent today along ever-busy four-lane Indiantown Rd. in Jupiter.   Adjacent to the road is a bald cypress swamp extending from the edge of the pavement back maybe half a mile or so.     The lichen diversity and coverage is conspicuously diminished with proximity to the traffic.

The case of the disappearing lichen.  The tree(s) in the foreground far from the busy road are rich in light-colored lichens.    Follow your eye out to the road…the darker trees near the road (such as those in front of the black car, or on the far left) have few or none.  All the trees are bald cypress.

 

Wind-Pollinated Oaks

Live Oak by John Badford

John and I worked today mostly on Oaks in Halpatioke Park in Stuart, Florida.   Many Oaks (and Pines) are shedding pollen now into the air, as we  allergy vics know so well.   Being that wind-pollinated plants are asserting themselves today,  let’s not talk about the birds and the bees, but rather the nerds in the breeze. Achoo.

Flowering plants are “all about” animal-mediated pollination.  Although there remains a ton to learn about the early evolution of flowering plants,  the standard perception is that flowering plants evolved from wind-pollinated ancestors, that their raison d’être is to offer attractants and rewards to creatures in exchange for symbiotic pollen transfer.   Yet over 10 percent of flowering plants are wind-pollinated. (I wonder if that will increase as we drive insect pollinators into oblivion.)

Myrtle Oak male catkins releasing pollen,  by JB

Wind-pollinated flowers represent a return to wind from insect-pollinated ancestors, that is, wind, then insects, then back to wind.   Why go retro?  Botanists estimate that the about-face has happened in over 60 instances.    Sometimes wind-pollination works better than bugs and birds, most obviously in circumstances where creature-based pollination is unreliable, such as harsh habitats and wide open spaces.

Wind-pollination is comparatively rare in tropical forests with high plant species diversity and plenty of birds, bees, moths, bats, and butterflies.  Wind-dependence becomes more prevalent in temperate and cold regions, and in places with high concentrations of relatively few plant species.    It would be pointless to dump pollen onto the wind where you are surrounded by different species.   But, by contrast, wind works if most of your neighbors are the same species as you, such as a prairie or marshland.  Not surprisingly then, most grasses and sedges are wind-pollinated.

Laurel Oak today, male catkin loaded with pollen ready to spew.

Many temperate- and cool-region trees are windy.  With these,  seasonality may matter.   In the early spring the temperate trees have no leaves to block pollination, yet insects and birds may still be scarce, and why compete for animal services when the wind is free, unlimited, and continuous nice and high in the treetops?   Why make nectar, make pretty petals, and have bees steal pollen if not necessary?  Why have a motorboat when a sailboat needs no gas?  Wind-pollinated trees include hickories, walnuts, chestnuts, ashes, poplars, and today, oaks.

Many wind-pollinated plants avoid airborne self-pollination by existing as separate male and female plants, although individual Oaks have both flower types in the same tree.   The male flowers are in dangling clusters called catkins well designed for shaking oodles of pollen out into the zephyrs.

The female flowers, fewer and solitary or in small groups, are tiny acorns-to-be with big stigmas acting like catchers’ mitts to snag the pollen from the air.

Female Laurel Oak female flower. Microscope view. Call it a future acorn, with the future acorn cap at its base.   The big dark-colored stigmas catch the pollen off the wind.