the Plant Kingdom

BIO 432 Field Botany

Phil Ganter

301 Harned Hall

963-5782

Rhododendron catawbiense, the Catawba Rhododendron - Found on the Blue Ridge in Virginia

There are hundreds of thousands of plant species known. More are being added every year. So, how does one get a view of the whole that contains enough detail to fill in the picture but not so much detail to overwhelm the main point? I think the best approach is to learn plant diversity in layers. We will need a taxonomy to work from and we will use the US Department of Agriculture's classification. It is "classic" in that it is pretty much the same as the one presented in textbooks prior to the molecular revolution in systematics. If you can get this one into your working, addressable memory, then the more current scheme will not overwhelm you. You must also go to the webpage on Plant Families to complete your work on plant diversity.

So, lets look at the big picture. What is a plant? What do plants all have in common? What seems to be a plant but is not? (The answer to this sort of question can often be very helpful.) Plants belong to the Kingdom Plantae. They all have plastids (remember that chloroplasts are but one kind and that, in plants, all plastids are related), but plastids are not unique to plants. Analysis of the circular DNA molecules of plastids supports the conclusion that all plant plastids are descended from a single ancestral taxon and that that taxon was a cyanobacterium. Algae are not plants. Some algae have plastids that are only distantly related to plant plastids. However, the green algae's plastids are closely related to plant plastids, so it appears that Plants and green algae share a common ancestor (there is other data to support this, but we don't need it here). However, although green algae and plants are related, there are enough differences to convince botanists that they belong in different kingdoms. So plants have plastids, almost all photosynthesize (some parasitic plants have given it up, although they still have plastids and can be identified as plants), and almost all are terrestrial. Some plants live in fresh water or float on its surface and a very few have invaded the oceans but only at the very edge where they can remain rooted and still get sunlight.

As someone who works with fungi, I should mention here that recently discovered plant fossils indicate that fungi may have played a role in the origin of plants. We know most plants today form mutualisms with soil fungi. Fossils from the time of the origin of plants have been found with evidence that the fungal partners were present from the very start. Perhaps it was the mutualistic pair that invaded the land from the water, each playing a vital role.

How do we divide up the kingdom. We will divide it into 12 divisions (this is the same taxonomic rank as phylum in the animal kingdom). However, we can group the divisions into two types: those without any vascular tissue and those with vascular tissue. Vascular tissue, remember, is the means by which plants move water and nutrients from the soil to the leaf and sugars and other synthesized organic molecules from the leaf throughout the plant. So these three divisions lack this valuable tissue and must rely on cell-to-cell communication and diffusion to move these things about.

The first and last are small (both in the size of the plants and the number of species in the group). The mosses, however, are fairly common and might be something to collect. They can be found in lots of places in Tennessee, especially in the mountains, where The USDA lists peak moss and Mt. Leconte moss as endangered species in Tennessee, Appalachian fir moss as threatened and Agoyan cataract moss, Clebsch's pocket moss, grimmia moss as species of "special concern." Don't collect these (it illegal) but locally we have lots in moist places and on forest tree limbs. Vanderbilt has a nice picture of moss. Because moss plants are small (that lack of vascular tissue!), don't get the impression they are hard to find. Where they grow, they often grow abundantly and are easy to spot in the aggregate.

We are already on to the next nine divisions. Some of these are rare or not common in our area and we can mention them only briefly. Once again, we can divide the divisions into groups. Within the nine vascular divisions, four do not produce seeds and five do. Let's discuss what a seed is first. A seed is a spaceship, just like a chicken egg. It is a protected environment where a young plant can survive until the external environment is suitable for growth. Seeds even provide resources to initiate the growth. But seeds are not synonymous with embryonic plants. Remember that they contain embryonic plants but also have a protective coating and stored resources. So all plants produce embryos, even the non-vascular plants, but seeds are a later adaptation to terrestrial life.

The only one I have not seen locally are the whisk-ferns. Two are uncommon but can be abundant if you find any. Horsetails are also called scouring rushes (they have a hard stem suitable for scouring, I guess) can be found along roadsides and in other disturbed environments. There is a nice shot of the stems and reproductive cones at Dave's Garden. The leaves are usually tiny and most horsetails look enough like one another and different enough from other plants that, once you have seen one, you can always recognize members of the division. Lycopods are not common either, but can be found in marshy areas or springs and some are found on the forest floor. The USDA has a gallery of lycopod photos.

Ferns are another story. Ferns are very common in this area and you might easily collect a fern. Ferns have a common look (the new leaves, called fronds, form fiddleheads as they unroll and grow). They are usually not hard to The Connecticut Botanical Society a nice gallery of fern photos. You might use it to confirm your identification. Most ferns in this area are easily recognizable as ferns. The green parts are the leaves (fronds). They develop from a stem, called a rhizome, that grows along the ground or just under it. Roots also grow from the stem. Recall from your freshman biology class that the fern described here is the sporophyte, the life history stage that produces spores through mitosis. The spores often develop in sporangia along the underside of the blade of some fronds. The sporangia are usually dark brown and easy to identify. Some species of ferns devote entire fronds to spore production. The other photosynthetic portion of the life history, the gametophyte, is usually small and not often seen in the field.

The seed plants, once again, can be divided into two groups (doesn't this consistent bisection make it easy to learn this particular taxonomy?): the cone-bearing seed plants and the flowering seed plants. The first group consists of four divisions:

The cones are the reproductive structures and come in large (female) and small (male) versions. Pine cones are female and the male pine cone is much smaller, found only in the spring and never hard and woody like a female cone.

Except for the Coniferophyta, all are small divisions and the only one of the three you might collect is the Ginkgophyta. The Ginkgophyta is a very rare division. It has one class, one family, one genus and one species. It is the ginkgo tree that is so common in Nashville. It grows well in temperate-zone cities and is a very popular tree with city landscapers. Its home is China. The Cycads are popular houseplants and are almost always misidentified as palms. They do look a bit like palms {[INSERT PICTURE OF CYCAD AND A PALM] but once you see the difference, it is easy to tell them apart. Cycads produce cones (large female cones that produce seeds and smaller male cones) and palms do not. Cycad cones are usually found at the top of the stem and you should look there if you are unsure of whether or not the plant you are examining is a cycad. The largest group of cone-bearing seed plants are the conifers, which means cone bearers. In biology (or English words in general), whenever you see a name that ends in -fer, -fera, -phora, -phor, -phore, -phera, or -pher, it means bearer.

The conifers are all trees and many are common in Tennessee. Their leaves are either scale-like or needles. I should also mention that conifer and evergreen are not synonymous terms. Most confers are evergreen and not deciduous (dropping all leaves simultaneously at the start of the cold or dry season) but there are exceptions. One native conifer, the bald cypress, is not evergreen. It drops its leaves every fall and grows new leaves in the spring, just like an oak tree. Evergreen trees also lose leaves but they never lose all at once.

Many conifers are popular landscape plants and these may come from almost anywhere. Common landscape plants are the yews and junipers found as hedges or bushes outside of buildings. Some pines are also easy to train into a bush form. Several non-native pines are popular. Recently, the dawn redwood has become a popular landscape conifer. It is an interesting story as it is often referred to as a "living fossil." The western US has two unusual conifers not found elsewhere: the redwoods and the sequoia. The redwoods are famous for being the tallest trees and the sequoias are not much shorter and their trunks are stouter, so they are claimed to be the largest trees by weight (although the kauri of New Zealand, also conifer trees, may be as large). The redwoods (there are two species) belong to the genus Sequoia and sequoia is the only species in the genus Sequoiadendron (that's a bit confusing). These two genera belong to a monophyletic group within the conifers along with a third genus, Metasequoia. Until 1941, Metasequoia was thought to be a fossil genus, i. e. although fossils were known, no living member of the genus was known. In 1941, a small grove of trees was found by botanists in China. The trees were obviously Metasequoia and were given the common name dawn redwoods to link the living trees to the fossils. Seeds were sent to botanical gardens all over the temperate zones and the tree proved to be fast-growing. Soon, it was being sold as a landscape plant. I wonder if those who planted dawn redwoods next to their houses in Tennessee know that those first specimens planted in the botanical gardens are now over 150 feet tall. They will dwarf the houses and crush them like a paper bag if they fall the wrong way. By the way, the dawn redwood is a second deciduous conifer, like the bald cypress.

Some Tennessee conifers are native, like the cedars you see in fields or along roads and several species of pine. The native conifers include some in eastern Tennessee that really shouldn't be here. The Smoky Mountains are high enough to provide a cool environment where firs , hemlock, and spruce can be found. They dominate northern forests and are found here because the last glaciation cooled Tennessee enough to allow them to replace the temperate forests here. As the temperature warmed and the ice sheets receded, the oaks, hickory, chestnuts, etc. characteristic of our temperate forests replaced the northern conifers except for the mountain tops. Biologists refer to the remnants of the conifer forests found in the mountains as relict communities. If they are lost, temperate species would replace them. Unfortunately, many species of northern conifer are declining in eastern Tennessee. Their death rates have been elevated and the causes are a complex mix of insect attack and stress due to human impact on their environment. Human impacts come through atmospheric pollution, acid rain, and global warming.

This brings us to the last division: the Magnoliophyta -- Flowering Plants. These are all of the flowering plants (remember that these are seed plants). This is over 90% of all of the plants and will probably be over 90% of your collection. The diversity here is too great to cover in a paragraph. So how shall we know them? We will have to get more detailed here. In taxonomy, more detailed means looking at lower-level taxa. The taxon below division in the standard taxonomic hierarchy is the class. We will divide flowering plants into two classes: Class Liliopsida and Class Magnoliopsida.

You probably already know something of this way of dividing the flowering plants. The Liliopsida are the monocots and the Magnoliopsids are the dicots. The mono- and di- refer to the number of seed leaves or cotyledons. These are not normal leaves but are storage structures found in the seed and there can be either one or two of them. Corn is a monocot and if you peel the seed coat from a kernel of corn you can see one large cotyledon and the embryo corn plant (its small, hard and at the base of the kernel). Peanuts are dicots and if you crack open a peanut shell, each peanut inside will easily split in two. These are the cotyledons. The embryo is found in between the cotyledons, which connect to the embryo, not to each other. Sometimes, the peanut embryo has tiny, unformed leaves. Being a monocot or dicot is more than having different seed anatomy. Most plants are dicots but the monocots are very important to humans. The Poaceae, the grass family, is a monocot family and contains important crops like corn, wheat, and rice. Monocots differ from dicots in several ways that it would be very good for you to learn so that you can tell to which class a plant belongs. The table below will summarize the differences:

You can explore these differences further (and, if you are confused about any of them, I recommend that you do) by going to the UCMP Berkeley page on Monocot/Dicot differences, which is very good for definitions (be sure the read the entire page, it's not long). You can see some diagrams of the differences on James Mannert's (from Texas A&M) page on Monocots-Dicots. You can get lots of diagrams and a more in-depth discussion of Monocots vs. Dicots in the Online Biology Book by M. J. Farabee on the Estrella Mountain Community College website.

Below is a condensed taxonomy. You are responsible for the overall scheme (related to the red terms) and for those divisions in blue.

`Academic``Page`	`BIOL 4320``Syllabus Page`
`Bio 432` `Page`	`Ganter``Home Page`
Plant Families webpage

	Monocots	Dicots
Cotyledon number	1	2
Leaf Veination	Major Veins Parallel	Major Veins Pinnate or Reticulate (net-like)
Flower Part Number	Multiples of 3	Multiples of 4 or 5
Stem Vascular bundles	Scattered Throughout Stem	In a Ring
Secondary Growth	Absent so no True Wood	Present in Woody Dicots
Root Origins	From Nodes on the Stem (Adventitious Roots)	From Radicle of Embryo