Botany Blog Plants of the Northeastern U.S.

December 23, 2009

Scented Liverwort

Filed under: North American Native Plants,Seedless Plants — admin @ 05:46

I recently updated the images on the page for Conocephalum conicum (Scented Liverwort), primarily to add an image of the sporophyte. They look like really small mushrooms, and the dark, round spots at the base of the ‘cap’ are the sporangia. Meiosis takes place in the sporangia and they eventually release spores.


December 18, 2009

Venus flytrap

Here are some of the “traps” of a venus flytrap, each consisting of a bi-lobed leaf at the end of a flattened petiole. They are active traps, meaning that they are capable of closing quickly to ensnare a prey item. Each lobe of the trap is beset with three large trichomes (the trigger hairs), readily visible in the image below. If any two of the hairs are touched, or if one of them is touched twice, this will cause a rapid pressure change within the cells and trigger the trap to close. The long segments along the edge of each lobe may look like sharp teeth but they are quite soft to the touch; they serve to prevent the escape of the prey, not to impale it.

Venus Flytrap

Venus flytrap (Dionaea muscipula) is a very popular plant, mostly owing to its ability to actively capture and digest insects. It has become widely available now due to the ease by which it can be propagated using tissue culture. Unfortunately many who attempt to grow this plant fail due to a lack of understanding of its cultural requirements. Understanding how to successfully grow this plant begins with understanding where it comes from and why it captures bugs in the first place.

Venus flytrap is the only species in its genus. It is in the family Droseraceae, which includes another group of carnivorous plants known as sundews (Drosera spp., e.g. Drosera rotundifolia). Unlike sundews, the venus flytrap has a much more limited natural range, originally found only in a small area of southern North Carolina and northern South Carolina. The natural habitat of this plant is open, acidic wetlands on peaty or sandy soils with low nitrogen availability. The capture and digestion of insects is an adaptation to these nitrogen-poor environments, allowing the plant to break down proteins and absorb the nitrogen for use in metabolic functions.

One mistake people make in trying to grow this plant is not providing it with sufficient humidity. Dry air causes the leaves and the traps to dry out and turn black. A glass or plastic cover satisfies this requirement; a small gap in the cover should exist to allow for some air circulation. Watering can be accomplished by standing the pots in shallow water. Distilled water is best, as hard water or water containing various salts (this would include softened water) will eventually kill the plant. While the plants can stand being in soil that is completely saturated for short periods, it is best to avoid this.

The question I am most often asked is if it is necessary to feed them. Not really, at least not as often as some would think. It is also best to feed the plants insects and not hamburger, although lean meats will work. I prefer to either set plants outside for a time in the summer to allow them to capture insects naturally or give a light dose of fertilizer to the leaves.

Lastly, there is the issue of dormancy. Venus flytrap occurs in temperate areas of the southeastern United States that experience occasionally low temperatures as low as 5 degrees F in the winter. In nature they go dormant in the fall as day lengths shorten and temperatures begin to fall. If plants are grown under natural light, as would be the case with a plant growing on a windowsill or outside, they must be allowed to go dormant and remain in that state for several months. Such plants could be kept in a refrigerator for that time. All of my plants, including those pictured here, have never been allowed to go dormant and continue to grow vigorously. I think the key to my success has been the use of artificial lights set on a long-day cycle and not allowing temperatures to fall below 60 degrees F. While my plants never go dormant they still manage to bloom occasionally. I usually cut the blooms to reduce the energy cost to the plants though.

Venus Flytrap Flowers

December 5, 2009

Polytrichum leaf cross section

Filed under: Seedless Plants — admin @ 20:52

Bryophytes, which include mosses, are known as non-vascular plants. Although mosses lack the vascular tissues xylem and phloem, many mosses posses water-conducting cells called hydroids and food-conducting cells called leptoids. Unlike the xylem of vascular plants, the hydroids found in mosses are not lignified.

Many mosses have leaves only a single cell-layer thick. A clear exception can be seen in a leaf of a Polytrichum sp. As seen in this image, the only parts of the leaf that are a one cell layer thick are the very edges. The midrib, or costa, of the moss leaf is seen in the center of this cross section towards the bottom.

Polytrichum leaf cross section

The thick layer of cells on the top of the leaf are called lamellae. They are like ridges that run parallel to each other over the length of the leaf and are several cell layers long and tall and a single cell wide. The lamellae are filled with chloroplasts and increase the effective area for photosynthesis to take place.

closeup of polytrichum leaf

Taking a closer look at the costa, we can see the water conducting hydroids that are visible as the larger row of cells near the middle.  These have large, empty spaces inside to provide ample space for water to flow. The cells above and below are the food-conducting leptoids and the surrounding cells with the thickened cell walls are called stereids. The stereids have a supportive function in the leaf.

In the future I plan to write an article on the life cycle of a moss similar to the one I did recently for a fern.

December 2, 2009

Fern life cycle

Filed under: Seedless Plants — admin @ 16:32

I snapped some pictures of various fern structures the other day and figured that I would do a little photo gallery showing the various stages of the fern life cycle. Unlike animals, the diploid stage (the one with two sets of chromosomes) in plants does not produce gametes. Rather, this stage produces spores via meiosis and is therefore known as the sporophyte (spore-producing plant). The sporophyte is the stage most familar to us, as seen in the following image.


The fern sporophyte produces leaves called fronds. On the back of the fronds of many species are often found little dots called sori (singular is sorus). To the naked eye they look like little brown spots like the ones below.


Even at this magnification the actual structure of a sorus is not clear. Zooming in a little further the surface begins to look a little rough.

fern sori

The reason for the rough appearance is the presence of the sporangia that make up the sori. The sporangia are not always visible because in some ferns they are covered by a structure called an indusium. In this particular species there are no indusia, so if the sori are viewed under a dissecting microscope and viewed at 3X magnification the sporangia become clearly visible.

Fern sorus with sporangia

One of my students described the appearance of the sporangia as bug-like. This is due to the row of large cells circling the outside of a sporangium. This is called the annulus and can be clearly seen if a few sporangia are scraped from the back of the frond and mounted with some water on a slide. The following image shows a sporangium viewed at 40X magnification.

Fern sporangium

Everything seen up until now has been part of the sporophyte and would be diploid. Inside the sporangium is where meiosis takes place, and this process results in the production of haploid spores from diploid cells. The spores are greenish or brown with a warty surface and several can be found within each sporangium. The annulus on the outside of the sporangium shrinks or expands with changes in moisture in the environment and helps control opening and closing of the sporangium. Under the right conditions the sporangium will open and release spores into the air. The image below shows several spores that were mounted on a slide and viewed at 400X magnification.

Fern spores

These spores can drift through the air until moist conditions set in, and then the spores will take on water and become heavier, at which point they will settle to the ground. If the environment is suitable the spores will germinate and develop into the haploid life stage known as the gametophyte. This progression from one life stage to another is known as alternation of generations and occurs in all plants. The fern gameotophyte is known as a prothallus and is often heart-shaped and green. They can vary in size but in some species may be up to a cm across. The following is an image of a fern prothallus viewed at 40X magnification after being stained and mounted on a slide.

Fern prothallus with antheridia

The little dots covering the surface of the prothallus are antheridia. Each antheridium is filled with sperm, the product of mitosis within those cells. Under moist conditions these sperm will be released to seek out eggs to fertilize. Eggs are sometimes produced on the same prothallus as the sperm, but in some species may occur on a seperate prothallus. Eggs are produced in specialized structures known as archegonia. Each prothallus can produce a single zygote that will develop into a new sporophyte. The zygote and subsequent sporophyte are diploid because they are the product of fertilization – the union of two haploid gametes (n + n = 2n). The developing sporophyte will appear as a short stem with a single leaf (shown at about 4X magnification as viewed under a dissecting microscope).

Fern gametophyte (prothallus) with a developing sporophyte

The sporophyte will be dependent on the gametophyte for a short time, after which the gametophyte will die and the sporophyte will become independent and develop into what we recognize as the adult fern.


Notice that no seeds are produced at any point in the life cycle. Ferns are known as seedless vascular plants because they have a free-living gametophyte and rely on spores for dispersal. The gametophyte is retained within the ovule of seeds plants (the ovule is what develops into the seed). Since ferns do not produce seeds, this makes growing them a bit more challenging, as it requires first sowing the spores and waiting for the gametophytes to develop, then providing a film of water in order for fertilization to occur. After that the process is similar to the handling of seedlings, although the young ferns may require a more humid environment until they mature.

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