The Squirting Cucumber

Plants have gone to great lengths when it comes to seed dispersal. One of the most bizarre examples of this can be found in an ambling Mediterranean plant affectionately referred to as the squirting cucumber. As funny as this may sound, the name could not be more appropriate. 

Known scientifically as Ecballium elaterium, the squirting cucumber can be found growing along roadsides and other so-called "waste places" from the Mediterranean regions of western Europe and northern Africa all the way to parts of temperate Asia. It is the only member of its genus, which resides in the family Cucurbitaceae. It is a rather toxic species as well, with all parts of the plant producing a suite of chemicals called cucurbitacins. In total, it seems like a rather unassuming plant. It goes through the motions of growing and flowering throughout the summer months but the real show begins once its odd fruits have ripened. 

A cursory inspection would not reveal anything readily different about its fruit. Following fertilization, they gradually swell into modest sized version of the sorts you expect from this family of plants. It's what is going on within the fruit that is rather interesting. As the fruit reaches maturity, the tissues surrounding the seeds begin to break down. The breakdown of this material creates a lot of mucilaginous liquid, causing internal pressure to build. And I mean a lot of pressure. Measurements have revealed that at peak ripening, pressures within the fruit can reach upwards of 27 atm, which is 27 times the amount of atmospheric pressure we experience when standing at sea level!

A cross section of the fruit showing the weakened connection point.

A cross section of the fruit showing the weakened connection point.

At the same time, the attachment point of the stem or "peduncle" begins to weaken. With all that pressure building, it isn't long before something has to give. This is exactly the moment when the squirting cucumber earns its name. The stem breaks away from the fruit, revealing a small hole. Within a fraction of a second, all of that pressurized mucilage comes rocketing outward carrying the precious cargo of seeds with it. 

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The result is pretty remarkable. Seeds are launched anywhere from 6 to 20 feet (1 - 6 m) away from the parent plant. This form of dispersal falls under the category of ballistic seed dispersal and it is incredibly effective. Getting away from the competitive environment immediately surrounding your parents is the first step in the success of any plant. The squirting cucumber does just that. It is no wonder then that this is an incredibly successful plant species. 

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

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

Pumpkins!

Ah, the pumpkin. Nothing signifies fall to me more than this lovely orange gourd. Who doesn't love the eerie glow of a jack-o-lantern or the pleasing taste of roasted pumpkin seeds? Don't even get me started on my love for pumpkin pie! This gourd has certainly ingrained itself in our culture but, from a botanical standpoint, pumpkins, or at least the species from which they hail, are quite interesting.

Cucurbita pepo is native to North America and is a member of the gourd family. Though it should come as no surprised, this group is characterized by the large fruits that they produce. The gourds themselves are actually a type of berry. C. pepo is one of the oldest species of plants ever domesticated. Records from Mexico show humans cultivating this species as far back as 8750 BC. The origins of this domesticated species are still a bit fuzzy but experts believe that C. pepo is a hybrid of Cucurbita texana and Cucurbita fraterna, though the former may just be a feral form of C. pepo.

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As it turns out, pumpkins are only one domesticated variety of Cucurbita pepo. Many of the gourds we enjoy are also varieties of this species. These include crops like acorn squash, delicata squash, gem squash, several types of ornamental squash (often called "gourds"), pattypan squash, spaghetti squash, yellow crookneck squash, yellow summer squash, and zucchini. Pretty impressive, no?

Many of these varieties are believed to have originated in the southern portions of Mexico but that is still being resolved. So, if you find yourself carving pumpkins and eating some other form of gourd, like spaghetti squash, realize that you are spending your evening celebrating the many uses of a single species!

Photo Credit: Thom Pirson & Wikimedia Commons

Further Reading: [1] [2] [3] [4] [5]

 

Mighty Mighty Squash Bees

It's decorative gourd season, ladies and gentlemen. If you are anything like me then you should be reveling in the tastes, smells, and overall pleasing aesthetics of the fruit of the family Cucurbitaceae. If so, then you must pay your respects to a hard working bee that is responsible for the sexual efforts of these vining plants. I'm not talking about the honeybee, no no. I am talking about the squash bees. 

If we're being technical, the squash bees are comprised of two genera, Peponapis and Xenoglossa. They are not the hive forming bees we generally think of. Instead, these bees are solitary in nature. After mating (which usually occurs inside squash flowers) the females will dig a tunnel into the ground. Inside that tunnel she places balls of squash pollen upon which she will lay an egg. The larvae consume the protein-rich pollen as they develop. 

The story of squash bees and Cucurbitaceae is a North American story. Long before squash was domesticated, these bees were busy pollinating their wild relatives. As a result, this bee/plant relationship is quite strong. Female squash bees absolutely rely on squash flowers for the pollen and nectar needs of their offspring. In fact, they often dig their brood tunnels directly beneath the plants. 

Because of this long standing evolutionary relationship, squash bees are the best pollinators of this plant family. The flowers open in the morning just as the squash bees are at their most active. Also, because they are so specific to squash, the squash bees ensure that pollen from one squash flower will make it to another squash flower instead of an unrelated plant species. Honeybees can't hold a candle to these native bees. What's more, crowds of eager honeybees may even chase off the solitary squash bees. For these reasons, it is often recommended that squash farmers forgo purchasing honeybee hives for their crops. If left up to nature, the squash bees will do what they are evolutionarily made to do. 

Photo Credit: MJI Photos (https://www.flickr.com/photos/capturingwonder/4962652272/)

Further Reading:
http://www.researchgate.net/profile/Victor_Parra-Tabla2/publication/226134213_Importance_of_Conserving_Alternative_Pollinators_Assessing_the_Pollination_Efficiency_of_the_Squash_Bee_Peponapis_limitaris_in_Cucurbita_moschata_(Cucurbitaceae)/links/549471010cf20f487d2a95b8.pdf

http://www.jstor.org/stable/25084168?seq=1#page_scan_tab_contents

http://extension.psu.edu/plants/sustainable/news/2011/jan-2011/1-squash-bees