A Rare Plant Treat

July 6, 2010

I was in Seattle recently and enjoyed a visit to the greenhouses at the University of Washington. I was delighted to find a collection of Welwitschia plants there, one of which was forming cones. This bizarre plant of the Namibian Desert belongs to the gnetophyte lineage of seed plants. It is one of three wildly different branches of this clade.

Welwitschia plants in the UW greenhouse have tall pots to accommodate their long tap roots.

The gnetophytes are one of five extant lineages of seed plants. The others are the cycads, the ginkgo, conifers, and the angiosperms, aka flowering plants. The angiosperms greatly outnumber the others, but that has become the case in the Cenozoic Era. In the Mesozoic Era, there were many other types of gnetophytes, but presently the three lineages are the genus Ephedra, genus Gnetum, and genus Welwitschia.

Although there are about 60 species of Ephedra and about 30 of Gnetum, there is only one species of Welwitschia, W. mirabilis. Ephedra species are native to arid environments in North and South America, Africa, and Eurasia. They have greatly reduced leaves and look like a bush of tough, narrow stems. Gnetum is the odd one on environment. It grows in the tropics of Indonesia, the Philippines, and parts of Africa. Most of its members are vines, although a few are trees or shrubs. Their leaves look very much like those of angiosperms.

Ephedra, a relative of Welwitschia, growing in Utah. The leaves of this bush are reduced to tiny scales.

Gnetophytes were once thought to be closely related to flowering plants, but the DNA told a different story. They are now considered to be more closely related to the conifers. Characteristics that all gnetophytes share include opposite leaves and having staminate and ovulate reproductive structures on separate plants, i.e. they are dioecious.

Welwitschia grows only two leaves, not counting its two seed leaves, in its whole life time. The leaves arise from a woody stem that has a sort of upside down cone shape. The plants are estimated to live about 1000 years, judging from their growth rates and the length of the leaves on wild plants. The leaves grow from their bases and often split so that it isn’t easy to see that there are only two.

The stem of Welwitschia is woody and has a roughly inverse cone-shape.

The two leaves of this Welwitschia plant are split into several strips. The top of its woody stem is visible.

One of the plants in the UW greenhouse had formed cones. It is a male plant, and there are stamens showing near the bottom bracts. The branch that bears the cones grows from the top of the woody stem, near the base of the leaves. I had read about their cones, but never seen them “in person” before, so finding them was a real treat. 

These are staminate cones of Welwitschia. Their stalk grows from the top of the woody stem.


Botany marches on – Part 1, basal angiosperms and monocots

April 13, 2010

Warning! I’m going to get into some detailed botany here, so if you are not deeply into the flowering plants and their classification and you do not own my book, A Tour of the Flowering Plants, you may not wish to wade through all this. It is basically for advanced elementary and secondary Montessori botany studies and for anyone else that owns the book. A Tour of the Flowering Plants is still quite useful to show the appearance of angiosperm families, whether or not you are concerned about the latest classification.

Last fall, the Angiosperm Phylogeny Group published a third report concerning the classification of the orders and families of flowering plants. The report, published in the Botanical Journal of the Linnean Society, is called APG III. There is a summary of APG III on Wikipedia. http://en.wikipedia.org/wiki/APG_III_system My book, A Tour of the Flowering Plants, is based on the 2003 report from this group, which is called APG II. The book has some further advances that were published on the Angiosperm Phylogeny Website of Peter Stevens. http://www.mobot.org/MOBOT/Research/APweb/welcome.html

I’ll go over the APG III changes, beginning with this post. If you own my book, you can decide if you want to add notes to it. You may contact me via my website (www.bigpicturescience.biz) if you would like a list of the pages and changes for bringing A Tour of the Flowering Plants in line with APG III.

Will the changes keep coming over the years as we acquire more and more DNA data? I think that future changes will be modest and will not affect the general structure of the angiosperm tree. There aren’t that many unplaced groups left. There will likely be little surprises, like one I give below for Nymphaeales.   

For now, let’s start with the first branches of the angiosperms, grouped as the basal angiosperms in A Tour of the Flowering Plants. The Nymphaeales got another family, Hydatellaceae, which was formerly placed in the grasses. This shows how much DNA studies can reveal, and what studies of morphology may not be able to distinguish. This family is tiny, both in size and numbers of species. The only reason I mention it is the idea that when plants adapt to living in water (or any other extreme environment), they often change form so much that they don’t resemble even their closer relatives. You can see the plant here: http://www.ubcbotanicalgarden.org/potd/2007/03/hydatellaceae_1.php

The order Chloranthales was previously unplaced – no one was sure what its closest relatives are. Now it is considered to be a sister group to the magnoliids. The magnoliids themselves have not changed in APG III. This branch of the flowering plants includes the laurel and black pepper families, as well as the magnolias. Although their seeds have two cotyledons, they are not closely related to the eudicots. The eudicots are the traditional dicots minus the magnoliids and the basal angiosperm lineages.

In A Tour of the Flowering Plants, I used terms for branches of monocots that have since disappeared. You don’t have to worry about whether to call the Liliales and Asparagales “lilioid monocots” or “petaloid monocots.” Just call them monocots and go on. The only lineage of monocots that gets a special name now is the commelinids. “Lilioid” and “petaloid” should be understood as informal terms that refer to plants that were traditionally lumped in the lily family. Most of them have large, showy tepals.

The major change in the monocot is the grouping of several small families as subfamilies under the enlarged families Amaryllidaceae, Asparagaceae, and Xanthorrhoeaceae. This is all within the order Asparagales. Here’s the breakdown:

The enlarged Amaryllidaceae has the agapanthus subfamily (Agapanthoideae, equivalent to the former Agapanthaceae), the onion subfamily (Alliodeae, equivalent to the former Alliaceae), as well as the amaryllis subfamily (Amaryllidoideae, equivalent to the former Amaryllidaceae). The members of this enlarged family have their flowers in umbels that are enclosed by two bracts when the flowers are in bud.

The enlarged Asparagaceae is really big. It has the Brodiaea subfamily (Brodiaeoideae), the scilla subfamily (Scilloideae, which includes the former hyacinth family, as the tribe Hyacintheae), the agave subfamily (Agavoideae, which includes the former Agavaceae), the Nolina subfamily (Nolinoideae, equivalent to the former Ruscaceae), as well as the asparagus subfamily (Asparagoideae). Yet another subfamily holds several Australasian species such as the cabbage tree, Cordyline.  

Asparagaceae members have flowers in racemes or in umbels that have three or more bracts at their base. The umbels, if present, do not have the pair of enclosing bracts seen in Amaryllidaceae.

The enlarged Xanthorrhoeaceae (the grass tree family) includes the daylily subfamily (Hemerocallidoideae) and the asphodel subfamily (Asphodeloideae), as well as the grass-tree subfamily. I did not include the grass tree family in A Tour of the Flowering Plants because it is native to Australia and not commonly used in North American landscaping.

The cattail family, Typhaceae, got a second genus, Sparganium, the bur-reeds. It’s not hard to see these two aquatics as relatives.

I’ll address the APG III changes to the eudicots in another post.


Postscript on slime molds

June 24, 2009
My tomato plant has a slime mold!

My tomato plant has a slime mold!

Slime molds seem to be traveling lately. For the first time, one of them appeared in a pot in my greenhouse. I was away for a few days and didn’t catch it in the act of crawling up on the side to form its spores, but there it is. I wonder if I brought the spores into the greenhouse on my hands or clothing after I found (and poked) the one under the juniper tree.

Once my cucumbers had mushrooms, a species that is considered a pest in greenhouses. I suppose it shows that fungi and slime molds spread themselves far and wide, like other organisms that depend on tiny spores for reproduction. Once in a while a spore lands in a good place to grow and that makes up for the huge numbers of spores that don’t grow into anything.


Stalking the wily slime mold

May 29, 2009
This slime mold aggregated under a juniper tree.
This slime mold aggregated under a juniper tree.

We have had a wonderful series of rains along the Colorado Front Range, and many moisture-sensitive organisms are showing up. The picture shows one of the less photogenic of the slime molds, probably from genus Fuligo. I was surprised to see this one preparing to form its spores in the thin duff under a juniper tree. The first time I saw it, it was a spongy, cream-colored mass. That day I hadn’t brought my camera – a lesson for me to be more prepared this time of year. I went back the next day and took this photo. The mass had shrunk and liquid pools appeared on its surface as it converted to spores.

Slime molds are incredible creatures that spend part of their life cycle as individual cells and part as a multicellular or multi-nucleate structure. They have a more attractive name – the social amoebas, but more information is listed under “slime mold.” The basic life cycle of social amoebas involves spores that germinate into individual cells. These amoebas eat bacteria from decaying plant materials. When food runs low, the cells send out a chemical signal that calls all of their kind to come together and make spores. The spore-bearing structures can be elaborate and beautiful, but they are small and easily overlooked. If you want to see a variety of them, go to this listing, http://www.uoguelph.ca/~gbarron/myxoinde.htm. For a story about hunting slime molds in the Great Smoky Mountains National Park, see this article from Smithsonian Magazine: http://www.smithsonianmag.com/science-nature/phenom_mar01.html. The Discover Life website has good information and photos as well: http://www.discoverlife.org/20/q?search=Eumycetozoa.

It is easy to bring a slime mold into the classroom. To make its home, you need an empty Petri dish or similar container, some paper towel, and few flakes of old-fashion oatmeal. Scientific supply companies sell the dried form of the organism, Physarum polycephalum. It is a resting structure called a sclerotium. If a slime mold in its active state dries out, it can form a sclerotium and hunker until the moisture returns. To grow the slime mold, cover the bottom of the Petri dish with clean, white paper towel, sprinkle in about a half-dozen flakes of rolled oats, and moisten this well, but don’t add so much water that there are puddles. Place the sclerotium in the dish. Don’t worry if it looks like lots of orange flakes – the parts will find each other and come together. Place your culture in a re-sealable plastic bag to retain moisture and to keep the slime mold from migrating out. Put the whole thing in the dark to prevent the organism from forming spores. The yellow slime mold will become active and move around the Petri dish. When you are finished observing the slime mold, you can put it in the light and use a magnifier to look for the spore-bearing bodies – small black structures that give it its name, the many-headed slime. To see photos of this slime mold in several stages, see the first link above. Here’s a link to more culture information: http://www.educationalassistance.org/Physarum/EasyToGrow/PHYSARUM%20culture%20for%20web.html.

Slime molds are members of the unikont branch of eukaryotes and the amoebozoa branch of unikonts. They make up the mycetozoa branch of amoebozoa. The term “myxomycetes” is used for the acellular slime molds, those whose amoebas fuse together into one big mass. Older classifications placed the slime molds in the fungus kingdom, to which they are only distantly related.

If you want to stalk the wily slime mold, a magnifier is a great help. Wet weather, decaying vegetation, and patience are also needed. Happy hunting!


Classifying buttons vs. life

April 13, 2009
 
Buttons can be classified in many ways

Buttons can be classified in many ways

If you want to teach someone about classification, a pile of assorted buttons is a good tool. It is always interesting to have two or more groups working on a button classification and see what criteria they use. Buttons make a fine model and come in enough variations to make classifying them interesting and even challenging. However, there is more to classifying life than classifying buttons. Life has another dimension.

 Buttons are here-and-now objects. Big buttons don’t have little buttons and they don’t pass on information to offspring. They have no history that we can observe and they share no ancestors. Buttons carry no information about their past. Classifying them is a good model for what Linnaeus did when he classified life. He felt, at least for most of his career, that all life had been created instantaneously and had always been and would always be just as he saw it.

Life has important differences from buttons. Darwin’s work was very important in calling attention to life’s history and to the idea of evolution, which he called descent with modification. We now have overwhelming evidence that life changes through time and all living species have a long history. Fossils tell a good deal of the story, but the “second fossil record,” the DNA in each organism, is what has allowed us discover much more of the story.

Each species had ancestors that stretch back in time. For the story of the many human ancestors, see The Ancestor’s Tale by Richard Dawkins. This inspiring book has its own Wikipedia entry, in which the ancestors it visits are listed. http://en.wikipedia.org/wiki/The_Ancestor’s_Tale Connie Barlow describes associated experiential activities for children at The Great Story website. http://thegreatstory.org/ancestors-tale.html

Two species may be descendents of a common ancestor that lived in the not-so-distant past. Biologists strive to place these sorts of close cousins in the same group, a lineage that includes the ancestor and its descendents. Other life may have shared an ancestor with our cousin species, but much further back in time, with many more lineages also sharing that far past ancestor. This may be shown on a Tree-of-Life diagram as a deeper branch from earlier in life’s history.

How can we model descent with modification? Once at a teacher’s workshop I used chocolate candy. We had plain miniature chocolate bars, bars with nuts, Hershey’s Kisses, and Hershey’s Hugs. We made a branching diagram that illustrated our hypothesis of the descent of these candies. The best part was eating the samples after we had finished with our phylogeny.

Maybe there is no suitable model for classifying life other than life itself. It certainly won’t be boring.


New Plant Kingdom ideas & new cards and chart

March 23, 2009

sori-leaf2
Sori on the leaf of a leptosporangiate fern

I recently revised my photo cards for the plant kingdom. They were previously called “Phyla of the Plant Kingdom.” With most of the phyla no longer being used, the title had to change. Now that set is called “Major Branches of the Plant Kingdom.” It still has 40 cards and each card still carries the classification on the back, but there have been changes to the text. I also put in some new photos, such as the one for the leptosporangiate ferns. There are new clearer photos for some of the mosses and club mosses. I’ve combined some illustrations onto one card and added two new families of conifers, the juniper/redwood family, Cupressaceae and the yew family, Taxaceae.

If you are introducing the plant kingdom to elementary students, I recommend the revised Plant Kingdom chart from InPrint for Children. http://www.inprintforchildren.com/store/  Carolyn Jones has done her usual high quality design job and added color to the individual illustration cards that go with the chart. Please note that she is closing retail sales soon, but her charts will be available from Montessori Services. http://www.montessoriservices.com/store/

New Plant Kingdom chart from InPrint for Children

New Plant Kingdom chart from InPrint for Children

I’d like to go back and make one more stab at explaining the changing view of the plant kingdom. The bryophytes still have phylum names, so I listed them on my cards, but it would be perfectly OK for precollege levels to simply call them by their common names – liverworts, hornworts, and mosses. These three lineages are monophyletic (“one lineage”) and they have a similar type of life cycle and yet it isn’t totally clear if they share a recent common ancestor. They could be shown on a separate branch or as three separate branches coming from the plant kingdom before the vascular plants branch off.

The first branch of the vascular plants is the lycophytes. If they are a phylum, then the other phylum would have to the euphyllophytes (“true leaf plants”), which is both the monilophytes (fern lineages) and the seed plants. If the fern lineages were to have phyla, there would have to be one for the whisk ferns and the ophioglossid ferns (adder’s tongue and grape ferns), one for the horsetails, one for an obscure group of tropical ferns, and one for the leptosporangiate ferns. The seed plants could have phyla for the gymnosperms and angiosperms or for each of the major seed plant lineages or??? More data is needed, but maybe it is just time to discard phyla for the plants. The view of the full lineage for each group is a much richer view.


(Disappearing) phyla of the plant kingdom

March 20, 2009
whiskfern

Whisk ferns are a part of the fern lineage. They are no longer a phylum.

I noticed last year as I was writing my book, Kingdoms of Life Connected, that plant systematics textbooks were not using phyla, except for the bryophytes in some cases. What’s going on here? It is nothing less than a new view of the plant kingdom and of the classification of life.

Our traditional view was set by Linnaeus, back in the mid 1700’s. His system was based on the assumption that all life had been created simultaneously and that it was unchanging. He based his work on the appearance of the organisms and placed them in the hierarchical categories that we still (sometimes) use – kingdom, phylum, class, order, family, genus, and species.

Now botanists look at the lineages for each group of plants. For example ferns can be seen as members of the plant kingdom (embryophytes), vascular plants (tracheophytes), true-leaf plants (euphyllophytes), the fern lineage (monilophytes), and finally the branch of the leptosporangiate ferns, sometimes called the true ferns. This is a much richer view than a simple box labeled “ferns.”

What Linnaeus missed is the history of each organism. Darwin bought forward the important idea that organisms have histories. Some share a recent common ancestor, others do not. The history of an organism doesn’t show up in a row of boxes. Instead it must be displayed as a branching diagram that shows which organisms are more closely related. 

Getting back to the plant kingdom and how we introduce it in the elementary classroom – usually the plant kingdom was broken into phyla (or divisions if you prefer the traditional name). Most of children’s literature – the small body of learning resources that actually address the plant kingdom – use phyla, whereas college texts and professional botany writings have largely discarded that category for plants.

Why have most of the phyla names been dropped? They didn’t work with the new view. The horsetails were previously placed in their own phylum, but they are embedded in the monilophytes, the fern lineage. So are whisk ferns, the psilophytes. The phylum name is even less useful for whisk ferns because it excludes their close relatives, the grape and adder’s tongue ferns.

Will phyla come back? It’s not impossible, but it may take a while for botanists to settle on what to call a phylum. Is it a branch of the ferns, the whole fern lineage, or the euphyllophytes? If children know the main branches of plant life, they are well-prepared whatever system develops. The animal kingdom, by the way, has kept its phyla, although they are now grouped into different lineages than they were a decade or so back.

Another term to discard is “seedless vascular plants.” The vascular plants have two branches, the lycophytes (club mosses and their relatives) and the euphyllophytes. The latter has two branches, the monilophytes (ferns in the broad sense) and seed plants. Club mosses shouldn’t be in the same category as the ferns, and “fern allies” mixes unrelated lineages.

For children to see the current view of the plant kingdom, they need a branching diagram that shows who is related to whom. Rows of boxes are out, phylogenies are in. A phylogeny is a branching diagram that illustrates a hypothesis about the evolution of organisms. Actually, the word applies both to the hypothesis and to its illustration. For more about current phylogenies, see my book, Kingdoms of Life Connected: A Teacher’s Guide to the Tree of Life and take a look at the charts that are available for free download from my website, http://www.bigpicturescience.biz.

 

Another term for a phylogeny is a Tree of Life or, informally, a family tree. The Tree of Life web project (http://tolweb.org/tree) has a great illustration in its home page. If you go to the page for the plant kingdom (aka embryophytes), you will see the extant lineages and a number of extinct ones. See http://tolweb.org/Embryophytes/20582. It is always thought-provoking to see the extant lineages in the matrix of extinct ones.


What should you do with your old plant kingdom charts? Keep them for historical perspective. Children’s literature still shows older classifications. Older charts also help children see the changing nature of science thought. Just make sure that children have working knowledge of the new, phylogenetic view of life.