Getting to Know Elodea

Photo by Christian Fischer licensed under CC BY-SA 3.0

When I think back on it, one of the first plants I ever actively tried growing was waterweed (Elodea canadensis). My 4th grade teacher had invested in a unit on the ecosystem concept. We all brought in 2 liter soda bottles that we craftily turned into mini terrariums. The top half of the terrarium was filled with soil and planted with some grass seed. The bottom half was filled with water and some gravel. In that portion we placed a single guppy and a few sprigs of Elodea. 

The idea was to teach us about water and nutrient cycles. It didn't work out too well as most of my classmates abandoned theirs not long after the unit was over. Being the avid little nerd that I was, I fell deeply in love with my new miniature ecosystem. The grass didn't last long but the guppy and the Elodea did. Since then, I have kept Elodea in various aquariums throughout the years but never gave it much thought. It is easy enough to grow but it never did much. Today I would like to make up for my lack of concern for this plant by taking a closer look at Elodea. 

An example of the soda bottle terrariums. Photo by Kara Nelson [source]

The genus Elodea is one of 16 genera that make up the family Hydrocharitaceae and is comprised of 6 species. All 6 of these plants are native to either North or South America, with Elodea canadensis preferring the cooler regions of northern North America. They are adaptable plants and can grow both rooted or floating in a variety of aquatic conditions. It is this adaptability that has made them so popular in the aquarium trade. It is also the reason why the genus is considered a nasty aquatic invasive throughout the globe. For this reason, I do not recommend growing this plant outdoors in any way, shape, or form unless that species is native to your region. 

Believe it or not, Elodea are indeed flowering plants. Small white to pink flowers are borne on delicate stalks at the water's surface. They are attractive structures that aren't frequently observed. In fact, it is such a rare occurrence that trying to figure out what exactly pollinates them proved to be quite difficult. What we do know is that sexual reproduction and seed set is not the main way in which these plants reproduce. 

Photo by R a mueller licensed under CC BY-SA 3.0

Anyone who has grown them in an aquarium knows that it doesn't take much to propagate an Elodea plant. They have a remarkable ability for cloning themselves from mere fragments of the stem. This is yet another reason why they can become so invasive. Plants growing in temperate waterways produce a thick bud at the tips of their stems come fall. This is how they overwinter. Once favorable temperatures return, this bud "germinates" and grows into a new plant. In more mild climates, these plants are evergreen. 

One of the most interesting aspects of Elodea ecology is that at least two species, E canadensis and E. nuttallii, are considered allelopathic. In other words, these plants produce secondary chemicals in their tissues that inhibit the growth of other photosynthetic organisms. In this case, their allelopathic nature is believed to be a response to epiphytic algae and cyanobacteria.

Slow growing aquatic plants must contend with films of algae and cyanobacteria building up on their leaves. Under certain conditions, this buildup can outpace the plants' ability to deal with it and ends up completely blocking all sunlight reaching the leaves. Researchers found that chemicals produced by these two species of Elodea actually inhibited the growth of algae and cyanobacteria on their leaves, thus reducing the competition for light in their aquatic environments. 

Elodea make for a wonderful introduction to the world of aquatic plants. They are easy to grow and, if cared for properly, look really cool. Just remember that their hardy nature also makes them an aggressive invader where they are not native. Never ever dump the contents of an aquarium into local water ways. Provided you keep that in mind, Elodea can be a wonderful introduction to the home aquarium. If you are lucky enough to see them in flower in the wild, take the time to enjoy it. Who knows when you will see it again. 

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] 

The Enemy of My Enemy is My Friend

Spotted Knapweed (Centaurea maculosa). Photo by Alan Vernon licensed under CC BY-NC-SA 2.0

Plants produce a lot of chemicals. I mean a lot. Some of these are involved in day to day functions like growth and reproduction. The function of others can be a bit less obvious. These are often referred to as secondary compounds as they are not directly involved in growth or reproduction. Some of these chemicals are toxic to other plants. We call these compounds allelochemicals. Producing allelochemicals can give some plants a competitive advantage by knocking back their neighbors. However, like most things in ecology, this situation isn't always that simple. 

Take the example of spotted knapweed (Centaurea maculosa). This nasty invader is wreaking havoc on plant communities throughout western North America. It wages its war under the soil where it releases a chemical from its roots called "catechin." This chemicla kills native plants, especially native grasses growing nearby. This competitive advantage can lead to total dominance of spotted knapweed in many areas where it quickly rises to monoculture status. 

Silky lupine (Lupinus sericeus). Photo by Andrey Zharkikh licensed under CC BY 2.0

Not all native plants are equally susceptible to spotted knapweeds effects. Two native forbs stand out above the rest in being able to cope with the allelochemicals released by spotted knapweed. Enter silky lupine (Lupinus sericeus) and blanketflower (Gaillardia grandiflora). Where these plants occur alongside spotted knapweed, other natives seem to do a bit better. This made researchers curious. What was it about these two species?

Blanketflower (Gaillardia grandiflora). Photo by Stan Shebs licensed under CC BY-SA 3.0

As it turns out, both of these natives secrete their own chemicals. These don't act as allelochemicals though. Instead, it was found that they neutralize the detrimental effects of the catechin. In doing so, both the lupine and the blanketflower create a safe zone for other natives to reestablish. This could be good news as it hints at new ways of approaching certain plant invasions. More work needs to be done to see how well this situation plays out in a natural setting but the evidence is tantilizing to say the least!

Photo Credits: [1] [2] [3]

Further Reading: [1]

Spurge of the Sidewalk

Photo by Harry Rose licensed under CC BY 2.0

Meet the prostrate spurge aka Euphorbia supina aka Euphorbia maculata aka Chamaesyce maculata. Whew, that is a lot of names for such a small plant. Taxonomic struggles aside, many of you have probably seen this small forb growing all over. From fields to parking lots, and even city sidewalks, this small member of the spurge family is an early colonizer of waste places where not much else can grow. I have seen this plant my whole life but never took any notice of it's flowers. I can't say I blame myself considering their diminutive size. Like many members of the spurge family, the latex-like sap can cause a skin rash in some people, so be aware of this when weeding your garden. It is native to the lower 48 but has been introduced far and wide thanks to human activity and it's resilience in poor habitats. In at least one study, leachates from prostrate spurge were shown to inhibit nodule formation on the roots of legumes. In essence, this species may be inhibiting other early succession plant species in order to maintain open habitat for itself for as long as possible. I must say, after finally taking a closer look at this species, I have developed a new found respect for it. 

Photo Source: Wikimedia Commons

Further Reading:

http://plants.usda.gov/core/profile?symbol=chma15

http://www.jstor.org/discover/10.2307/2441417?uid=4&sid=21102522714117

Ubiquitous Bracken

Photo by certified su licensed under CC BY 2.0

Bracken ferns are a true success story if there ever was one. They occur in temperate and subtropical regions of every continent on the planet except for Antarctica. They very well may be one of the most widely distributed ferns on the planet. In late spring, their unmistakable fiddle heads poke up out of the soil like some sort of alien life-form and quickly unfurl into a giant, beautiful frond.

Known scientifically as Pteridium aquilinum, some authors treat all common bracken fern as a single species. Others feel that the group should be broken up into something like 10 different species. That will be a debate for another day. The fact of the matter is, bracken are very robust plants. As long as they can get enough light, bracken can handle a wide variety of habitat conditions. They thrive on human disturbance and thus are considered rather weedy or even invasive in many habitats.

With ambling rhizomes these plants can rapidly spread to saturate open habitats. Large populations are often referred to as bracken barrens. Their establishment and persistence is aided by the production of allelopathic chemicals, which can limit the establishment of other plants. This is especially true following fires. However, where forests are sparse, dense stands of bracken can actually provide a shaded haven for woodland herbs that would otherwise not be able to establish.

Photo by Thayne Tuason licensed under CC BY-NC 2.0

Bracken is not only toxic to plants, it is also highly toxic to animals. Bracken produces hydrogen cyanide when young fronds are damaged, quickly poisoning whatever may be munching on the frond. It also contains chemicals that cause uncontrollable rapid molting in insects, leading to a quick demise for any bug unlucky to have fed upon this fern. They also produce a chemcial known as ptaquiloside, which is highly carcinogenic in mammals.

With ample defenses and a hardy disposition, it is easy to see why these ferns are so successful. Coming across a large patch of these plants is, to me, a beautiful sight. It is the ultimate irony that we continue to create the very conditions that cause them rise to invasive status. If anything, they stand as a reminder that we humans are simply part of a greater ecological system, not masters of it.

Photo Credits: Thayne Tuason (http://bit.ly/1JVvfBz) and certified su (http://bit.ly/1FpIYRF)

Further Reading: [1] [2] [3]