Saturday, March 11, 2017

Mosses of Central Florida 20. Polytrichum commune

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

Polytrichum commune Hedwig (Polytrichaceae) is the giant among Florida mosses, with stems up to 10 cm. long. The stems are upright, with numerous stiff, narrow leaves.  It is not common in Central Florida, but when  found,  it is usually in extensive, dense colonies.
A colony of Polytrichum commune growing near Ft. Lonesome, Florida, in
Hillsborough County.  Many of the shoots in this picture bear clusters of sperm-producing antheridia at their tips. Photo by Steve Dickman.
There are seven species of Polytrichum found in North America, out of 70 worldwide.  P. commune is found throughout North America, Eurasia, New Zealand and Australia.  I recently found it in Taiwan.

The single specimen with sporangia at USF
shows the impressive dimensions of
Polytrichum commune. It comes from
northern Florida.
The leaves in the Polytrichaceae are unusual in consisting mostly of a massive midrib covered with vertical sheets of tissue arising from the upper surface.  This makes viewing the leaf anatomy more difficult, but the edges of the leaf in Polytrichum commune are lined with distinctive sharp teeth.  The bases of the leaves flare out into a broad sheath, and only here can one see the shapes of the cells.

 The upper surface of a Polytrichum leaf is covered with vertical,
blade-like sheets of tissue, here seen in cross section.
Photograph by Kristian Peters; Creative Commons
Attribution-Share Alike 3.0"
The midrib of Polytrichum commune is thick and fills the entire
blade.  Distinctive hard teeth line the edges.

The base of the leaf flares out into a thin
sheath, where the cells can be seen to be quite
narrow and elongate.

Evidently, Polytrichum commune rarely produces sporangia in Central Florida, as we have   We have o such specimens in the USF herbarium.  I can only speculate on the reasons for this.  In order for sporangia to form, sperm cells must swim from the tip of a stem where they are produced to the tip of a stem where eggs are being produced.  The large size of Polytrichum commune would make the conditions where this process could take place rather rare, particularly in the relatively hot and dry climate of Central Florida.  The species is at it's southern limit here. The one specimen with sporangia I've seen was collected in northern Florida.

 In addition, the colonies of Polytrichum are unisexual - they produce either sperm or egg, so two colonies of different sex must intermingle for sexual reproduction and spore-formation to take place.  The size of the plants would add to the difficulty of such mingling, and it is possible that some colonies in our area were established by a single spore, and hence unisexual.  In the photo  of living plants in Hillsborough County above, the colony appears to be all male.

Incidentally, in the process of researching this species, I found another excellent blog site for mosses from the University of British Columbia. Check it out for general information about the different groups of mosses.

Wednesday, March 8, 2017

The nearly forgotten art of comparative plant anatomy 1. Wood

The study of human anatomy is an obviously essential subject for all medical students, and most of us  have a basic idea of where our liver, lungs, large intestine, etc. are located - important information for identifying and fixing health problems.

Comparative anatomy, on the other hand, is about the differences and relationships among different organisms.  Most of what we know about dinosaurs comes from their bones.  Dinosaurs with bones of similar shape and arrangement are considered closely related to one another, and so we can reconstruct not only individual dinosaurs from their bones, but also phylogenies (family trees) and classifications.  Bones, by certain structural characteristics can also give us clues about what dinosaurs ate and whether they were warm-blooded or cold-blooded.

The comparative anatomy of plants has been put to similar use, helping us to interpret fossils, as well as to help identify and classify living plants.  Wood anatomists can identify the genus, and often the species, of a particular wood sample, and this is put to use by archaeologists and forensic scientists as well. How often has Abby from the hit TV show NCIS led her colleagues to a crime scene in the woods, by identifying wood, leaf, or pollen fragments from a murder victim's body or clothing?  Wood scientists, like those at the USDA's Center for Wood Anatomy Research, maintain a library of wood samples, including thin sections for microscopic examination.

The academic study of plant anatomy has, however, been in decline for decades (see Dengler 2002) .  This is partly because of the decline in botany courses in general, but also because of the need to make room in biology curricula for the massive amount of new material in ecology, cell biology, genetics, DNA sequencing, genomics, etc.  Plant anatomy in particular is considered by many to be old-fashioned, having largely been "done" in the 19th and early 20th centuries.  The study of plant anatomy, traditionally taught by looking through microscopes at prepared slides and making drawings, is admittedly tedious, requiring an interest and passion that is rare among most modern students.  To be of any use, one must acquire a broad knowledge of the different cell types and tissues of plants, and to recognize them as they vary in form from one species to another.  So it is a type of training, involving "memorization" of terminology and structural detail that is incompatible with the emphases on principles, theory, and experimental methodology in modern biology courses.  Moreover, the specialized equipment and skilled personnel for making thin microscope slides is rarely found anymore in biology departments.

Yet there is so much that we can learn still by comparing the anatomical structure of different kinds of plants.   Aside from practical applications in forestry, forensics and archaeology, it is still important in understanding the relationships and adaptations of plants in general.  The next few postings will illustrate some of this.

Let's start with the obvious: the structure of wood.  We will note first that plants are simpler that animals, and in plant anatomy, we're talking more about tissues than organs, actually more about what they would call histology in animal studies.  A tree trunk, composed of wood and other tissues is a single organ, so it is the different layers of tissues and cell types that determine how it functions, how it is adapted for its environment, and how one species differs from another.

True wood, as found in gymnosperm and dicotyledonous trees, consists of layers of xylem tissue added each year that increase the thickness of the trunk, branches, and roots.  Each layer is made up of water-conducting cells, and various sorts of supportive cells ranging from thin-walled parenchyma to thick-walled fibers.

The wood of  balsa (Ochroma pyramidale) is soft and light because the supportive
tissue around the large vessels is thin-walled.
 Photo from  Curtis, Lersten, and Nowak, University of Wisconsin, Stevens Point.

As an extreme example, the wood of the balsa tree is radically different from from that of a
teak tree, allowing us to not only recognize each under the microscope, but also telling us something about their different life styles.  Balsa is a fast-growing, short-lived tree that colonizes disturbed areas in forests and then gives way to longer-lived trees with more durable wood like mahogany or teak.  The density of wood is determined primarily by the abundance and distribution of fibers around the thinner-walled water conducting cell.  Durability is also enhanced by preservative chemicals secreted into the wood.
Among the great variety of dicotyledonous trees, there is great variety in the shape, arrangement, and abundance of these different kinds of cells. This variation has resulted in some woods being superior for fine cabinetry, others for resilient baseball bats (ash), durable bowling pins (hard rock maple), or strong shovel handles (hickory or ash). The wood database contains extensive images and data concerning the characteristics and uses of different kinds of wood.

In the tropical hardwood teak (Tectona grandis), the supporting tissue around the large vessels is made up mostly 
of narrow, thick-walled fibers.

In temperate trees, such as this red maple (Acer rubrum) the annual growth rings of wood
(horizontal bands) are marked by distinct boundary layer of smaller, thick-walled cells laid down in the Fall,
something you don't see in tropical woods.  The vertical bands of cells are made up of living
parenchyma cells, often with thick secondary walls.
The flexible woody stems of grape vine (Vitis spp.) contain exceptionally wide
rays of parenchyma tissue that separate the narrow wedges of vessels and other
supportive tissues.
The simpler, softer wood of conifers, like pine or fir, consists mostlyof a single type of relatively narrow cell, the tracheid, which combines strength with water-conducting ability.  As angiosperm trees diversified, ancient tracheids diverged evolutionarily into two kinds of cells. Strength and density functions were taken on as some cells developed thicker walls, becoming fibers.  Water-conduction was focused in other cells that remained thin-walled, but became wider, and shorter: the  stacked cylindrical cells of the vessels.  There is also a network of parenchyma cells that permeate the wood as flat rays or vertical strands
The wood of conifers in general is very simple, consisting mostly of  tracheids, which conduct water as well as provide
structural support for the tree.  The band of narrower, thick-walled cells running across the bottom of the image is a
boundary layer, marking the slowing and  cessation of growth in the Fall.  Above it, the uniform mass of cells produced
in the Spring and Summer.  

In pines and some other conifers, the uniform growth of
cells is interrupted by large resin canals.

In monocots, the ability to produce layers of wood was abandoned as their ancestors evolved underground stems and clonal lifestyles.  When some of them became trees again, as in palms or bamboos, their water-conducting cells remained in separate vascular bundles scattered throughout the interior of the stem and surrounded by dense sheaths of fibers.
The dense, wood-like property of a palm trunk is provided by dense masses
of fibers, not layers of xylem laid down in rings. In this preparation, the walls
of the fibers are stained green rather than the usual red.
The rigid wall of a hollow bamboo stem is filled with  fibrous bundles.

On-line wood anatomy resources:

Curtis, Lersten, and Nowak, Photographic Atlas of Plant Anatomy, revised 2015

Schoch,W., Heller,I., Schweingruber,F.H., Kienast,F., 2004:  Wood anatomy of central European Species.

Meier, Eric,  The Wood Database.

Inside Wood, North Carolina State University, developed by Elizabeth Wheeler and others.  This site is more technical, and contains the most extensive library of wood anatomy images.

Thursday, March 2, 2017

Special Announcement - Botany bill in US Congress

Americans - A rare bipartisan effort to support botanical research needs the support of your Congressional representative and Senators.

This is not the party vs party politics we're all so tired of.  This is about Americans who care about the environment and biodiversity working together to make a better world for future generations.  Contact your representatives to urge support of this bill.  

Below is the full announcement from the Botanical Society of America:

ACTION ALERT: Co-sponsors needed for H.R. 1054 - The Botanical Sciences and Native Plant Materials Research, Restoration and Promotion Act
We are thrilled to announce that The Botanical Sciences and Native Plant Materials Research, Restoration and Promotion Act (aka the “Botany Bill”; bill number H.R. 1054) was introduced by Representative Quigley (D-IL) and co-sponsor Ros-Lehtinen (R-FL) last week! 
Background info: Read the official Billsummary of the main points, and the press release about the Bill from Representative Quigley. To-date, 62 professional organizations have endorsed the bill. Updates on the progress of the Bill can be found on the Plant Conservation Alliance Resources page. You can also track the Bill’s progress here.
We need your help!
Now that the Bill has been formally introduced, additional co-sponsors on both sides of the aisle are being sought. If you support the Bill, AIBS asks that you please call your representatives and voice your support for H.R. 1054 AND ask your representative to co-sponsor the Bill. Bi-partisan support will be required for the Bill to be introduced on the floor of the House of Representatives
How to prepare for your call/meeting
The following links provide information to help you prepare for your call/meeting with your Representative.
  1. Talking points on botanical science and native plant issues
  2. Summary of relevant funding language in the Department of the Interior Appropriations Bill 2017 (refer to talking points above for more information).
  3. Tips on meeting with a legislator or member of staff
Note that there is no companion legislation in the Senate yet.
If you have any suggestions for members of the House of Representatives that may be interested in co-sponsoring, or if you would be willing to reach out to your representative directly to let them know about this legislation and ask them to become a co-sponsor, please contact

Find an easy way to take action through the AIBS Legislative Action Center where you just enter your zip code to contact your representative about this Bill.
BSA Office
4475 Castleman Ave.
St. Louis, Missouri 63110
PH 314-577-9566, FAX 314-577-9515
American Journal of Botany -
Applications in Plant Sciences -
Plant Science Bulletin -
Botany Conference -

Sunday, February 19, 2017

Mosses of Central Florida 19. Rosulabryum capillare and R. pseudocapillare

Although the leafy shoots are buried within a
different moss, the presence of this Rosulabryum
is evident by the abundant and very large sporangia,
or capsules.
[For other mosses in this series, see the Table of Contents]

Like many other groups of mosses, those in the family Bryaceae are difficult to identify.  The available keys are highly technical and difficult to for non-specialists to follow.  The two species of Rosulabryum are presented together here because of those difficulties. R. capillare (Hedwig) J. R. Spence (Bryaceae) is common throughout North America, including Canada and our western states.  According to Flora North America, it is not found in Florida, but the related species R. pseudocapillare (Besch.) Ochyra takes its place.  However, numerous collections made in Florida have been identified by experts as R. capillare, along with many labeled as R. pseudocapillare.

Here, some leafy shoots have been isolated.
They are upright and radially symmetrical,
and the stalks of the sporangia arise from
the bases of the shoots. Sporangia are
symmetrical, cylindric and nodding.
Rosulabryum pseudocapillare typically has numerous thread-like reproductive structures (filiform gemmae) in the upper leaf axils, at least when not producing sporangia, while those of R. capillare do not.

Rosulabryum is common in Central Florida  and produces abundant nodding, nearly cylindrical sporangia (capsules) in the springtime.  It can be found most readily in wet soil at the margins of receding ponds, forming mounds of upright stems. It might almost be considered weedy, as it also pops up readily in pots containing wet, organic soil, and in wet soil along sidewalks.

Rosulabryum was formerly included in the genus Bryum, having been segregated out on details that are hard to follow in the formal keys.  In Florida, only Bryum argenteum remains in the original genus, which incidentally gives its name to the entire clade of non-vascular plants we call Bryophytes.  B. argenteum differs from Rosulabryum in its more compact growth form, its grayish coloration, and leaves that press flat against the stem when dry.  The dried leaves of Rosulabryum twist around the stem.

Nearly ripe sporangia of Rosulabryum
are cylindrical and bright green.
The leaves of Rosulabryum become twisted when dry.
The other segregate from Bryum found in Florida is Gemmabryum, but it apparently forms sporangia less often than Rosulabryum, relying more on asexual bulbils and gemmae for reproduction.  When sporangia do appear, they are more egg- or pear-shaped.  The leaves in Gemmabryum are also said to be pressed flat against the stem when dry, as in Bryum argenteum, rather than being twisted like in Rosulabryum.

Leaves of Rosulabryum, like other members
of the famly, have a strong midrib (or costa).
Leaves in the Bryaceae have a strong midrib, and the leaf cells are mostly large, more-or-less rectangular or rhomboidal in shape, thin-walled, and with numerous distinct chloroplasts.  This, along with the upright, mound-forming stems and the nodding sporangia, makes members of the family fairly easy to recognize, though the genera and species are more difficult to distinguish.

Leaf cells of Rosulabryum, are thin-willed,
revealing many distinct chloroplasts within.

The leafy shoots of Rosulabryum peudocapillare produce
many thread like reproductive structures called filiform gemmae,
while those of R. capillare rarely do.

Monday, January 30, 2017

Teaching biodiversity

The biodiversity crisis is one of the most pressing issues facing mankind.  But what is biodiversity? How does it come about?  Why are there so many kinds of organisms?  And what are the consequences of lost biodiversity?  Sounds like something we could devote a whole course to in our undergraduate curriculum.  But when we do, it's usually only to a handful of upper level ecology students.  What about our general student population, all those pre-meds we educate, or the public at large?  We would like our general citizenship to be well-informed on the dimensions and importance of biodiversity, but at the very least, our own biology majors should be not only informed, but also advocates.  How are we all doing on that?

The one, and sometimes only, opportunity we have to reach all of our undergraduates is in freshman biology.  A second opportunity comes if we can get students to take an organismal course like introductory botany, invertebrate zoology, mycology, or entomology.  The following suggestions apply equally well to all such courses, but I will focus on Freshman Biology, which in my university is taught in two separate one-semester courses: Cellular Processes and Biodiversity.  We use one of the standard large college texts for introductory biology.

The second course, Biodiversity, sounds good, but it has an ambitious amount of material to cover.  It is divided roughly into three sections:  Evolution, Diversity, and Ecology.  The section on Diversity, which might get five weeks out of the semester, is usually a rapid march through the kingdoms and phyla.  Plants usually only get 1-2 weeks of discussion in lecture,  fungi even less, more often than not by an instructor who has not had much training in botany or mycology.  The sections on animal and plant biology in the textbook are largely ignored in our courses, but they contain much additional information that can and should be brought in to help elucidate biodiversity issues.

The net result is that after this course in Biodiversity students have only a superficial introduction to diverse kinds of life, and have no real understanding of why there are so many different kinds of organisms.     The coherent biodiversity message will only  emerge if an experienced and skillful instructor is motivated to do so, and willing to synthesize material from different parts of the book.  The more we can integrate our discussions of evolutionary and ecological principles with questions about biodiversity, rather than treating them as three separate topics, the better. This is a tall order for the limited time available in a freshman course, so you have to choose your battles carefully.

Here are some ideas, with links to my blog essays that discuss these topics in detail:

1.  Think in terms of  adaptation.  This is the key concept  that links evolution, ecology, and biodiversity together. Adaptation is what results from the evolutionary process, it defines how organisms interact with their environment, and it is what differentiates the distinctive lifestyle of one organism from another.  Organism A is different from organism B because, since their common ancestry, they have had different adaptive histories, and have diverged into different lifestyles.  They have come to live in different environments  or to survive in the same environment in different ways.
The flowering structures of skunk cabbage are
adapted for getting a jump on the spring
flowering season by generating sufficient heat
to melt their way through the remaining snow.
Photo by Sakaori, from Wikimedia Commons

2.  Every feature has a function.  Everything we see in an organism, from the shape of a leaf to the color of tail feathers in birds, has some adaptive function, or did sometime during the adaptive history of the organism.  There is a story for every characteristic feature of a species.  Pollination biology presents many attention-grabbing examples.

3. "What good is half an eye?" Make use of some of the great questions posed by anti-evolutionists (though answered wrongly by them).  By focusing  on a single topic, like vision, one can trace the origins of light detection in bacteria, through the simple eyespots of protists, the simple eyes of flatworms, and then the diverse kinds of eyes found in cephalopods (squids, octopi), insects, and vertebrates.  There never was half an eye, always light detecting systems that became more complex and varied over time.  We can even bring in plants with their light-detecting systems  involved in phototropism (bending toward light), and photoperiodism (determining when plants bloom.)

 4. "If humans evolved from apes, why are there still apes?"  Another great question that illustrates the diversifying nature of evolution.  From the common ancestor of chimpanzees and humans, the chimp lineage continued to hone their adaptations for life in the forest, while human ancestors adapted for life in the open savanna, with skeletal changes that allowed them to stand upright and walk comfortably on two legs.  Students really take interest in human evolution, and so it is worthwhile to spend time on it.

Animals are eating machines, with mouth and eyes at the
front end, and locomotory organs along the side. Their
food resources are in compact packages - other organisms -
that they digest internally.
2. "What is the difference between plants and animals?"  I always began my botany classes with this question.  Almost everyone starts with the observation that plants are photosynthetic and animals eat stuff. True as it is, it is only  the beginning. The next thing that might come up is that animals move and plants don't.  Then as an instructor, you ask "why?"   Asking why is not to be anthropomorphic.  It's really asking "what are the adaptive advantages for plants not to move?"

Plants are anchored in one spot and create
branched systems above and below ground for
gathering diffuse resources. Meristems continually
create new roots, twigs and leaves.  And materials
are transported internally by manipulating water

One can then direct the discussion to the stationary, indefinitely branching body of a plant, adapted to create  an expansive antenna system for gathering light and other diffuse resources, in contrast to the discrete bodies of animals with mouth and sensory organs at the front end, and locomotory organs along the sides.  One must then discuss the system of meristems that enable varied plant architectures built of repetitive leaf-bearing units, and the hydrostatic nature of plant cells and plant processes that substitute for muscular activity in animals.

3. Why are there no moss trees? Everyone knows, at least by the time they get to college, how animals make babies.  The varied equipment and various strategies for getting sperm and egg together are a wonderful theme for exploring animal diversity, but how do plants do it? Plant (or fungus) reproduction, however, is always a challenge.    If you're stuck in one spot, and a potential mate is 50 meters away, how do get your sperm to her?  The astute student will immediately shout "pollen grains."  But how many know that there are actually sperm cells produced within pollen grains, and that pollen grains, and the structures that house the eggs are actually tiny. haploid individuals?

Eggs and sperm cells in ferns are produced on a
separate, independent, short-lived plant
(gametophyte)  that develops from a spore
released from the main plant (sporophyte).
Meiosis occurs during the production of the
spores, rather than in the production of gametes.
From Haupt, A. W. 1953. Plant Morphology.

That brings up the dreaded life cycle.  Students hate them and instructors who don't know their significance tend to skip over them. Memorizing a life cycle does not explain why life cycles exist.  What is the adaptive value of having separate tiny haploid plants to bear the sperm and eggs?  The place to begin is with ferns.  There is adaptive value in breeding with distant, genetically different individuals.  That would be impossible if the fern plant produced sperm and egg cells directly, as sperm cells on dry land can't get very far.  So instead, it produces spores, which can easily disperse over great distances.  Often enough, spores from genetically different ferns land together, These spores then germinate to produce tiny gamete-producing plants that can breed with one another.  The fertilized eggs then develop into a new fern plant.

The leafy, long-lived phase of a
moss life cycle is the egg and
sperm producing gametophyte.
The simple sporophytes consist
only of a single sporangium and
its stalk, which develops from
the fertilized egg, and which
remains attached to the gametophyte
plant for its short existance.
The answer to the question about moss trees is that a moss is actually a gamete-producing plant, and must remain small so it can mingle with genetically different plants for successful reproduction.  Mosses lack independent spore-producing plants, having instead small diploid spore-producing structures that emerge directly from the fertilized eggs, but remain attached to the parent plant. Thus there is no part of the moss life cycle that can get really large.

 Pursuing these sorts of discussions is of more value than memorizing the characteristics of all the phyla of invertebrates, or the differences between club mosses and horsetails.  Horsetails can be brought in, however, as an early example of the kind of multiple elongating (intercalary) meristems used by bamboos for their rapid growth in height.(convergent evolution).  Ultimately, we can try to understand why there are so many kinds of plants, and how to avoid the extinction of all those species.