Mosses of Central Florida 13. Philonotis longiseta

Philonotis longiseta clings to rocks along the edges of babbling
brooks. Specimen preserved as Essig 20150402-1 (USF).

[For other mosses in this series, see the Table of Contents]


Philonotis longiseta (Michx.) E. Britton  (Bartramiaceae) is a moss of wet places.  It is most often found on rocks or banks of streams, where it is constantly splashed and misted by rapidly moving water. It was said by Reese (1984) that it rarely forms sporophytes in the coastal Gulf of Mexico region, but I recently found it beside the artificial stream at the USF Botanical Garden in Tampa with abundant ripe spore capsules.  What exactly about this spot favors reproduction is not clear. Perhaps, the species requires a very stable situation, without drying or submergence, and such conditions are rare along Florida waterways.  In the constantly flowing artificial stream, however, the plants are continuously misted.


The midrib, or costa, extends as a sharp tip at the end of the leaf.  Cells are
rectangular and more elongate in the central part of the leaf. 

The leafy shoots are upright, forming bright green spongy masses clinging to the vertical rock surfaces. Leaves are stiff, long-triangular and have a prominent midrib that extends as a point beyond the tip of the leaf.  Leaf cells are elongate-rectangular, with usually a small papilla (hard, clear bump) at the upper end of each cell.


The spore capsules are frequently surrounded by
drops of water that form from the continuous
 misting.

The most distinctive feature of the genus, and others in the family that are not found in Florida, are the very round spore capsules, causing them to be generally known as apple mosses.  They form at the ends of long stalks rising from the bases of the leafy shoots.

Several other species of Philonotis have been reported from Florida, but are rare, and differ in minor ways.  P. longiseta occurs throughout eastern North America, the West Indies, Central and South America.



Reference:
Reese, W. D. 1984. Mosses of the Gulf South: From the Rio Grande to the Apalachicola. Louisiana State University Press.

Mosses of Central Florida 12. Forsstroemia trichomitria

Forsstroemia trichomitria forms a shaggy mat on the
trunk of a Liquidambar tree along the Hillsborough River
in west-central Florida. Photograph by Alan Franck.

[For other mosses in this series, see the Table of Contents]


Forsstroemia trichomitria (Hedw.) Lindb. (Cryphaeaceae) is an epiphytic moss that forms luxurious mats on hardwood trunks in moist forests.  It is found throughout eastern Asia as well as eastern North America and northeastern Mexico.  It is in the same family as Cryphaea glomerata, recently featured here, and has a very similar habit.  I am grateful to my colleague, Alan Franck, for the new collection and photographs of this species in the field. Alan was recently appointed curator of the USF Herbarium, and shares my interest in mosses and other "cryptogams."

The orange capsules are conspicuous among the upturned
leafy shoots. Photograph by Alan Franck.

The leafy shoots spread out from the trunk and curve upward slightly.  The leaves are ovate to long triangular, and are said to usually have a midrib.  In this specimen, the midrib is weak and disappears in mid-leaf.  The cells of the leaf are elongate and curved, but not as long as in Isopterygium and its relatives, with thick clear walls between them.  The leaf cells of Cryphaea are short and roundish.

The ovate-triangular leaf of Forsstroemia trichomitria has distinctive folds
along both edges.  A weak midrib can be seen
toward the torn bottom of the leaf. From Franck 3785 (USF).

The cells in the central and upper part of the leaf are
elongate, tapered, and slightly curved, with conspicuous
clear cell walls between them.

In both Cryphaea and Forsstroemia the stalks of the spore capsules are short, presumably due to their epiphytic habit.  They are elevated on the trunks and branches of trees, and so only need to drop their spores to get them into the air.  Mosses that live on the ground need long stalks to get their spores into a good launching position.  The stalks of Forsstroemia are a somewhat elongate and their capsules are fully exposed, while  those of Cryphea remain hidden within a nest of bracts.

The orange capsules are pushed out a short distance from the leafy shoots.
A ring of yellow teeth around the capsule mouth serves to push spores out 
as it alternately moistens and dries out.  
Photo from the dried specimen (Franck 3785, USF)

Mosses of Central Florida 11. Haplocladium microphyllum

Haplocladium microphyllum is frequently found growing in wet, sandy soil
in lawns.

[For other mosses in this series, see the Table of Contents]


Haplocladium microphyllum (Hedw.) Broth. (Leskeaceae)  is a creeping, mat-forming moss that is widespread globally, across much of Eurasia, South America, and in North America from Florida to Texas and up to southern Canada.

This species superficially resembles Isopterygium tenerum.  They are both prostrate, mat-forming mosses growing at the bases of trees, but Haplocladium is more likely to be found on soil, frequently in lawns, and often found on or near concrete or other alkaline materials.  Their capsules are essentially indistinguishable from those of Isopterygium, without examination of minute technical details.

Haplocladium colonies can sometimes be seen creeping
up on bricks or concrete surfaces.

The capsules of Haplocladium are curved to the
side as in Isopterygium.

The leaves of Haplocladium are short but slender-tipped, and
have a prominent midrib.

It is in their leaves that Haplocladium can be most easily distinguished from similar species.  The leaves of Haplocladium are shorter, but with more prolonged tips, and more pressed against the stem than those of Isopterygium, especially when dry.  The leaves also have a strong midrib, lacking in Isopterygium, and the cells are roundish to square, instead of long and worm-like.  The cells are also papillate, i.e. with short, hard, pimple-like projections.

The leaf cells are squarish and have a single hard
papillum (seen as a bright spot on the out-of-focus
cells to the sides). Part of the midrib is on the left.

Species in the genus Entodon have a similar creeping habit, but their capsules are upright and cylindric.

Plant Life: a Brief History

If you've enjoyed these botany professor essays, you'll probably also find "Plant Life: a Brief History" of interest.  It was written in the same spirit, but provides a more complete narrative of the evolution of photosynthetic organisms from their ancient beginning as cyanobacteria, to their dizzying diversity as flowering plants.

I wrote this book to provide a different way of looking at the the fundamental features of plants, as well as to trace their evolutionary history.  In this chronological approach, the critical features and processes of plants are presented as they arose in adaptation to new habitats or lifestyle opportunities.  Adaptation is the key process of evolution and also provides  explanations for why plants are the way they are and why they do what they do.

Plant Life: a Brief History showcases some of the best
botanical line art from  classical botany texts.  This
illustration of different forms of mosses is from the classic
"Natural History of Plants," by Kerner & Oliver, 1895.
A. Polytrichum commune; B. Bryum caespiticium;
C. Hylocomium splendens; D. Sphagnum palustre.

Photosynthesis was an adaptation, a series of adaptations in fact, for taking advantage of the huge untapped source of energy coming from the sun.  The cyanobacteria that perfected it proliferated into vast numbers and dominated the Earth's ecosystem for two billion years.  And so the story began.

Everything else, from why green algae have flagella and red algae don't, to why monocot leaves have parallel veins, can be explained as adaptations to particular environmental challenges or opportunities.  While we don't know for sure the details or circumstances of some of these adaptations, we can be sure that nothing about plants came about accidentally or without value to their survival. For the adaptive events of plant evolution that are still shrouded in mystery, I provide some plausible scenarios, including some that are still controversial.

The detailed structures of Psilotum and Tmesipteris
are crystal clear in this illustration from the "The Plant
Kingdom," by William F. Brown, 1935.  Reprinted
with permission from the Brown family.

This book also highlights another aspect of history: the marvelously detailed line drawings of the great botanical texts written in the 19th and early 20th centuries.  There is a vast treasure of such illustrations out there, and I have chosen a number of them to illustrate the various plants we encounter in the book.

The book is designed as a supplement for students, a refresher for teachers, a primer for non-botanists whose research or teaching touches upon plants, and as an introduction to plants and their evolution for the general reader.  Because of this broad intended audience, technical jargon has been kept to a minimum.

A preview is posted on the Google Books website, which includes the table of contents, the introduction, and the first chapter. It is available from Oxford University Press USA or U.K. and other major booksellers.  It is also available as an eBook from many online booksellers.

If you can't purchase it at this time, please ask your local or school library to obtain it.

In the meantime, we will continue with more adventures on this blog site.  Stay tuned!

Mosses of Central Florida 10. Cryphaea glomerata

Cryphea glomerata grows on branches of hardwood trees. Photographed in
Hardee County by Alan Franck, USF Herbarium, 

[For other mosses in this series, see the Table of Contents]

Cryphaea glomerata Schimp. ex Sull. (Cryphaeaceae) is unusual in several respects.  It grows relatively high on the branches of hardwood trees in moist forests, and the sporangia are on very short stalks.  It is found throughout the eastern US, from New Jersey to Florida and west to Texas and Oklahoma.

Cells of the leaf are small and roundish, with thick walls.
From Franck 3699 (USF).

The stems are horizontal with leaves more-or-less flattened in a plane.  Leaf cells are flattened-roundish, with thick walls, and a midrib extends most of the way through the leaf.

Sporophytes are produced sporadically along the stems and are sessile (lacking a long stalk), remaining embedded within a cluster of sharp-tipped bracts. The unusual positioning indicates that long stalks are of no advantage to mosses that spread their branches from high vantage points, allowing them to provide greater protection for the sporangia.

A related species, Cryphea nervosa, is also found in Florida, and differs only in its more prolonged, sharp-tipped leaves, and the capsule teeth being more deeply embedded.

The family Cryphaeaceae is closely related to the Leucodontaceae, and not well-distinguished, making the genus Forsstroemia the most closely related genus locally.

Sporophytes (arrows) are produced sporadically along the leafy stems
and remain embedded within a nest of protective bracts.
From Franck 3699 (USF).

Mosses of Central Florida 9. Sematophyllum adnatum

Sematophyllum adnatum forms tangled mats of elongate leafy
stems.  It is distinguished from mosses of similar habit
by the leaves that curve strongly to one side.
(Essig 20060516, USF)

Revised 2018 Mar 20, with new photos of leaf cells.

[For other mosses in this series, see the Table of Contents]

Sematophyllum adnatum (Michx.) E. G. Britt. (Sematophyllaceae) is one of the most common mosses in Florida, and also occurs westward into Texas, northward to New York and Ohio, and in tropical America.

It resembles other common mosses, such as Isopterygium tenerum, in that it forms thick mats of straggling leafy stems primarily on the bark of tree trunks, particularly live oak trees, and fallen logs.  It differs from other straggling mosses most conspicuously in the way the leaves curl to one side, particularly as they dry out, and in the capsules, which are slightly asymmetric, but erect, not strongly curved the way they are in Isopterygium.  

Leaf cells of Sematophyllum are narrow, tapered, and somewhat
worm-like, but with thinner walls than in Isopterygium.  From
a dried herbarium specimen (Essig 20160119-2, USF)

The leaves gradually taper to a narrow point. 

The leaves are similar to those of Isopterygium and other members of the Hypnaceae, with slender, worm-like cells, and lacking in a costa, or midrib.  The leaf tips are generally not toothed like those in Isopterygium, and cells at the basal corners are more inflated. The capsules are also similar to those in the Hypnaceae, with two rows of teeth around the mouth.  Sematophyllum is presently separated in the Sematophyllaceae, which is scarcely distinguishable from the Hypnaceae. 

How plants do everything without moving a muscle

So more about the difference between plants and animals. In my last post ("Why we must teach botany"), I indicated that photosynthesis dictates immobility, and that the inability to move has ramifications for all other aspects of plant life.  One of the challenges of teaching botany is to convince students that organisms that don’t look or behave like their pet hamster are in fact far more interesting!  And as it turns out, our favorite things about plants, from flowers to flavorings, only exist because plants can't move.

Plants must spread their tissues thinly in light-
gathering antennas known as leaves, with an
equivalent underground system of water and mineral-
gathering roots.  This architecture makes
movement impossible.  Pictured is a species of
Tetrapanax from China.

The word “animal” means something that moves, as in the word “animate.”  Why don't plants also move?  Wouldn't it be useful for them to pick up and move to  a better lit or more fertile location, or to swat away annoying herbivorous insects?  And how do plants have sex if they can't move?  It all begins with how animals and plants feed themselves.

Animal food comes in the form of concentrated, nutrient-dense packages: other organisms. Animals move in order to locate, go after, capture, and consume these discrete food items.  Secondarily, they move to reproduce, escape danger, or defend themselves.  These activities require muscles, nerves, senses, a mouth and an internal digestive system.  When animals became multicellular, their cells wrapped compactly around the central digestive cavity, and one end became specialized for feeding and coordinating movement. An animal body is therefore discrete, streamlined, and highly organized, with a distinct head for sensing and biting, fixed locomotory organs along the sides, and, in most, a rear end for excreting wastes.  

   

The resources needed by plants, on the other hand, are diffuse: carbon dioxide, light, water, and dissolved minerals.  In order to efficiently gather these far-flung molecules and photons, plants must spread their tissues broadly and thinly, and behave more like antenna systems than hunters; the more they spread, the more resources they can gather. So inherent to the plant lifestyle is indeterminate growth - the ability to grow, branch, and expand their antenna systems indefinitely.

Some single-celled algae move about in response to light
intensity, but this is impractical for multicellular plants, as
simple flagella would have to be replaced by muscles, a
 coordinating nervous system, and a streamlined body ill-
suited to photosynthesis.

Single-celled, flagellate algae like dinoflagellates, euglenoids, and some green algae do move in response to light and other stimuli, but as plant life became multicellular, the costs of motility apparently outweighed the benefits.  How would you push a satellite dish through the water, or march a tree across a savanna?  The shape requirements for motility and for photosynthesis are architectural opposites, but for every reason animals have found movement necessary, plants have found alternate strategies. 

The famous photosynthetic sea slug, Elysia clarki, would seem
to be an exceptional animate "plant."  Sea slugs must still
obtain their chloroplasts by ingesting algae, and so still need
the full motility apparatus of animals. If a sea slug were able to
pass its chloroplasts onto its offspring and never have to eat
again, its descendants would most likely gradually lose their
ability to move as they expanded their photosynthetic surface
further, and perhaps even take up a plant-like habit of branching
and indeterminate growth.

If a plant becomes shaded, for example, it can usually branch out and extend into a light patch.  A vine thus finds its niche in a dense forest.  Roots likewise can extend toward moister or more fertile patches of soil.   So indeterminate growth can relocate antenna systems as well as expand them, making motility not only difficult, but also unnecessary.   

The plant body is what it needs to be for efficient photosynthesis, but without moving parts, how do plants, particularly terrestrial plants, do anything else?  How do they circulate water and food, for example?

Animals circulate food, water, and wastes through a muscle-driven circulatory system. Lacking that, plants have developed a simple passive system that operates pretty much like a paper towel.  The walls of plant cells are made of cellulose, which by no coincidence is the material paper towels are made of.  Water moves upward into a paper towel, even defying gravity, because of the magnetic attractions among water molecules and cellulose.  The plant is a giant, complex paper towel sopping up water from the soil. Evaporation of water at the top of the plant pulls more water up from the roots, keeping the entire system saturated and moving (see How does water get to the top of a redwood tree?). This is transpiration, which requires no energy expenditure on the part of the plant and no moving parts. 

For other activities, plants exploit something called turgor pressure, which in turn is the result of the enigmatic process of osmosis.  The short description of osmosis is that water tends to move into cells, causing them to expand.  If that works for you, you can skip to the next paragraph.  The explanation for why this happens is more complicated.  The net movement of water across a cell membrane is from areas of higher water concentration (e.g. distilled water) into areas of lower water concentration (i.e. a solution of other molecules), even though it would seem that the latter area is already “crowded.”  Water molecules move randomly in both directions, but since there are more of them outside the cell than inside, the number entering at any moment is greater than the number that are exiting.  The other molecules in the cell cannot exit as easily, so the cell just gets more crowded.  As the total number of molecules bumping around inside the cell increases,  the pressure increases.  Incidentally, the opposite happens when you put a cell into salt water – water leaves the cell and it shrivels.

The leaves of the venus fly trap snap shut around prey by
manipulating osmotic water pressure. Water pressure
in cells (turgor pressure) drives their expansion
during plant growth, and also maintains the crispness
and upright posture of soft plant parts.  It also
moves dissolved food around the plant through the phloem.
Water tension resulting from transpiration pulls water
upward, sometimes 100 meters or more.  All this happens
without muscles or nervous system. 

 A naked animal cell in fresh water will expand until it bursts.  Plant cells, however, are surrounded by rigid cellulose walls that do not allow the cells to expand.  So the pressure builds up to the point at which it starts forcing water molecules out of the cell at the same rate they enter through osmosis.  The pressure then stabilizes and we know it as turgor pressure.

So healthy plant cells are pressurized, and this creates a force that plants exploit in a variety of ways, replacing the force of muscular activity in animals. Turgor pressure is what keeps soft plants upright, and lettuce crispy.  It causes young cells with soft walls to expand during growth of shoots and roots.  It is also the basis for venus flytrap leaves snapping together, through a sudden decrease in turgor pressure.  In the phloem tissue, sugar is actively pumped into specialized cells, resulting in even more osmotic pressure.  These cells are connected in long tubes and the pressurized fluid flows to areas of lower pressure, where sugar is being actively removed.  Thus sugar may flow from leaves to roots, or from roots to new shoots, flowers, or fruits.

How do plants reproduce while stuck in one spot?  The answer, my friends, is blowing in the wind (with apologies to Bob Dylan!). Sperm cells can move only short distances and must remain wet.  Sexual reproduction, on land at least, can therefore occur only between individuals that are literally touching one another. To be worth the trouble, however, sperm cells must unite with eggs from a genetically different individual.  While animals run around in frantic hormone-driven pursuit of a mate, plants have a sublimely simpler solution: they release tiny airborne spores to serve as genetic couriers. 

When we see a fern in the forest, we're looking at the
sporophyte generation, which produces spores asexually.

The gametophyte generation of ferns
is a small, independent, short-lived green
plant.  Sexual reproduction occurs
between adjacent gametophytes.  The
resulting fertilized egg will develop
 into another full-sized fern
 (the sporophyte).

Ferns, for example, produce thousands of tiny spores that swirl around in the breeze, and which with luck land next to spores produced by genetically different individuals.   Each spore grows into a tiny, specialized, short-lived plant, and it is these tiny plants, the gametophytes, that undergo sexual reproduction.  Sperm cells from one swim the short distance to the eggs produced by another.  (The full-sized plants that produce the spores are called sporophytes). The life cycle of a plant thus consists of the alternation of  full-sized individuals with tiny ones. (See “the truth about sex in plants.”)

In flowers, such as this orchid in the genus Cypripedium,
the gametophyte generation is hidden within seeds
and pollen grains. The elaborate structures of flowers
are devices for luring insects and
other animals to carry sperm-containing pollen grains
from one immobile plant to another.

The gametophytes of seed plants are even tinier than those of ferns and hard to see.  A pollen grain is a fancy spore that moves sometimes great distances and carries within it the tiny 3-celled sperm-producing gametophyte.  The egg-producing gametophyte is likewise hidden away inside an embryonic seed (ovule).  So when a pollen grain is delivered to a pine cone or a flower by wind or insect, it brings sperm cells directly to the eggs. Plants can thus reproduce with genetically different individuals that may be miles or hundreds of miles away, and they don’t have to move an inch.

Finally, without the ability to run, hide, or bite, how do plants defend themselves against the hoard of vegetation-munching insects, grazing mammals, and other herbivores? They have a variety of tricks, but primarily what they do is to make themselves toxic or at least distasteful to most animals.  Plant are master chemists, and have continually come up with new poisons to counter the ever diversifying array of vegetarians.  Those poisons, incidentally, are the sources of our medicines, drugs and spices, as well as overt poisons.  The difference between a medicine, or even a spice, and a poison is a matter of dosage.

Spices, such as the yellow curcumin from the rhizome of
turmeric plants (Curcuma longa), are chemical defenses against herbivores,
as are other substances we use as drugs, medicines, poisons, resins, etc.
Photo by Simon A. Eugster, posted and licensed on Wikimedia Commons,

Plants can also create physical barriers that deter animals from even taking a bite: layers of dense fibers or bone-like sclereids within their tissues, or spiky thorns, spines, and prickles on the surface.  Grasses and some other monocots invest relatively little in chemicals, but regrow rapidly from their leaf bases after an attack of herbivores.  

Plants thus achieve all of life's basic functions without moving a muscle, and flourish in great variety and numbers.  A lion can growl and bite and claw its way through an existence of a couple of decades, but a tree can live for 5000 years.