Yellow Starthistle Tops the Plant "Most-Wanted" List

At first glance, the Yellow Starthistle looks like a beautiful wildflower.... one that you would be delighted to view during a nature hike.  However, this plant has quickly risen to the top of the "plant most want listed" as an invasive species in the United States. As you know, an invasive species is one that is introduced into an area or habitat to which it is not native.  In this new area, the checks and controls that keep a species from overpopulating are not present.  As a result, the species increases so rapidly that the local (and native!) species are often driven to extinction.

The Yellow Starthistle ( Centaurea solstitialis) is native to Eurasia. It grows as part of balanced ecosystems there because it is kept in check by a variety of local herbivores, as well as other plant species that have co-evolved with it in its native habitat. It is thought that the Yellow Starthistle was introduced into California in the 1850's during the California Gold Rush when imported alfalfa seed arrived that was contaminated with the seed from the Yellow Starthistle.  Once introduced into the United States, it quickly took hold, and has been problematic ever since.

Here is the quick-list of facts about this highly invasive species:

• A single staked plant may produce a root system that extends to an area of three feet outward from the stalk.  It rapidly depletes moisture in the soil and out-competes the local and native species in its ability to obtain water.

• It has become very common along roadsides, pasture lands, and wildlands.  
• It is poisonous to horses and causes a disease called "chewing disease."  This can be fatal to the horse if treatment is not received.  Horses are the only animals known to be affected.
• The plant may grow to a height of 5 feet.
• Seed output may be as high as 30,000 seeds per square meter.  
• Invasion of the species is increased by cars along roadsides and by livestock.  Livestock that is suspected of ingesting the Yellow Starthistle should not be shipped to uncontaminated areas.

Yellow Starthistle seedling

What are methods of controlling this invasive species?  In 2003, 4 insect species were introduced from Europe as a means of control.  These agents of biological control included 2 weevils and 2 flies. Each of these insects lays its eggs on the flower/seed head of the plant and, as a result, reduce the number of seeds that the plant produces. All four insects are host-specific to the starthistle and do not attack native species.  Grazing animals such as sheep, goats and cattle are also an effective means of control.  A variety of chemical agents are also used.

In an interesting, but sad turn of events, the Yellow Starthistle has invaded and is quickly taking over the Sierra Nevada habitats in Yosemite National Park.  You can read all about Yosemite's attempts to control this plant at this link.

The Giant Corpse Flower

A giant flower that smells of rotting flesh??

Yep, this is the Giant Corpse Flower, or scientifically speaking,  Amorphophallus titanum.  (Appropriate name, huh?)

This recently caught my attention when I was on my daily prowl on the internet searching for fun and interesting bits of science news to share with my students in my biology classroom.   It seems that Cornell University has a giant corpse flower that recently bloomed.  It was only one of 140 plants to bloom in cultivation in recorded history.

As you know, in angiosperms, the flower is the reproductive organ of the plant.  For true land plants reproduction is tricky business.  In order to be adapted to life on land, the plant must find a way to get its sperm to the egg of a different (but of the same species) plant.  Sperm cells are placed inside pollen grains, and then pollen grains must be effectively delivered to nearby flowers.  Pollen can be carried by wind or water, but many plants depend upon the insect pollinators to deliver their sperm cells.  The flower that can best attract these pollinators has the best chance of having its eggs fertilized.

Now back to the giant corpse flower.  This plant produces one of the largest flowers on record.  When it opens, the smell is said to be horrific, mimicking the odor of dead, rotting flesh.  The smell attracts dung beetles and flies that feed on carrion.   When the insects crawl into the flower, their bodies are covered with pollen.  The insects exit the flower, and move on to the next flower, transferring pollen from flower to flower as they go.

The news about the blooming of the flower at Cornell University was perfect timing for me.  I was in the process of teaching angiosperm reproduction to my biology students.  I did a quick YouTube search and found two short, but excellent videos to show my classes.  The first is called "Corpse Flower Blooms at Zoo" and is about a blooming that occurred at the Cleveland Zoo.  It has wonderful photography and my students were captivated by it.

The second video was a clip from The Private Life of Plants by David Attenborough.  This clip is called "The Largest Flower in the World."  This video is just a few minutes longer, and contains information about other plants, as well as the corpse flower.  But anything by Attenborough gets shown in my classroom....I may be his biggest fan!  Now, here is the neatest bit of information about the corpse flower being used in The Private Life of Plants.  Sir David felt that the constant use of the scientific name (Amorphophallus titanum) during his documentary would be inappropriate, so he invented the popular name of "titan arum" to use during the filming of his show.

To wrap up this lengthy post, here are a few fun and interesting facts about the giant corpse flower:

• It is referred to as the corpse flower because it emits an odor resembling dead, rotting flesh.
• Flowers are either male or female.  The female flower opens first.  A few days later the male flower open.  This prevents self-pollination.
• The titan arum grows in the wild only in the equatorial rainforests of Sumatra, Indonesia.
• The plant blooms rarely in the wild, and even less often when cultivated.
• In 2003, the tallest bloom in cultivation was achieved at the Botanical Garden of the University of Bonn in Germany.  The bloom was 2.74 m (8 ft 11 in) high, and was recorded in the Guinness Book of World Records.
• This record was broken in June of 2010 when a flower reached the size of 2.74 m (8 ft 11 in) high in a nursery in New Hampshire.