#pedaliaceae

Dispersal by Open Sesame!

In certain instances, “open sesame” might be something you exclaim to magically open the door to a cave full of treasure, but for the sesame plant, open sesame is a way of life. In sesame’s case, seeds are the treasure, which are kept inside a four-chambered capsule. In order for the next generation of plants to have a chance at life, the seeds must be set free. Sesame’s story is similar to the…

Uncarina grandidieri; succulent seasame

Pedaliaceae (Lamiales)

This interesting succulent, native to Madagascar, has leaves resembling cotton leaves, flowers similar to Thunbergia or Petunia, and some pretty sharp fruits, but it is interestingly related closely to sesame!

Marie Selby Botanical Gardens, Sarasota, FL (May 2016)

Meet Proboscidea louisianica aka the Devil's claw plant. The common name comes from these nasty looking seed pods that evolved to latch on to large mammals that brush up against them. The genus Proboscidea has traditionally been placed into the sesame family (Pedaliaceae), due to superficial similarities in flower and seed morphology, but more recent work has moved it into the unicorn plant family, Martyniaceae. That's right... unicorn plants.

The entire family is found in the New World, with P. lousianica hailing from arid parts of southern North America. There are some aspects of this species that make them quite interesting to botanists. For starters, the apt name of Devil's claw given to the seed pods comes from their spiny nature. They become entangled in fur quite readily. The odd thing about this seed dispersal mechanism for P. louisanica is how big the seed pods are. Until cattle were introduced to this continent, animals large enough to effectively disperse these massive seed pods were missing, having gone extinct at the end of the last ice age. It is believed that this plant may be an anachronism of this era.

The flora we are familiar with today on this continent spent millennia co-evolving with ice age megafauna like mammoths and giant ground sloths. There is a growing school of thought waking up to the idea that many close relationships probably developed over this time and have not yet been lost due to the relatively limited amount of time since the extinction of these large mammals. There are some people who will tell you that the seed pods are designed to ensnare small mammals like mice and cause them to die, allowing the seeds to germinate in their rotting corpses. I was unable to find any evidence in support of these claims.

Another intriguing anatomical feature of this species are the countless sticky glands that cover the entire plant. These readily ensnare insects that land on or try to climb up the plant. Analysis of the fluids secreted by these glands show evidence of digestive enzymes but the jury still seems to be out on whether or not P. louisanica is undergoing any active carnivorous behavior. It is more likely that these glands are a form of defense against insect herbivores and indeed they work quite well. Even a brief run-in with this plant leaves you quite sticky and slimy. It is possible that by ensnaring herbivorous insects, the plant can attract carnivorous insects that will eat the herbivores and then "repay" the devil's claw with nutrient-rich feces. To ad insult to injury, the plant kind of smells. It has been likened to old gym clothes. Either way, it is believed that these kinds of defensive mechanisms are a good example of how early carnivorous behavior may have evolved in plants.

This is a neat plant. I have had fun growing them in the past. They are an annual but may reseed if care is not taken to removing the seed pods before they pop open. Because of their lively appearance and the unique look of their seed pods, these plants are often grown as horticultural oddities. Be careful though, as they have escaped cultivation outside of their native range and can be considered a noxious weed!

Photo Credit: John Loo

Further Reading: http://plants.usda.gov/core/profile?symbol=PRLO

http://aob.oxfordjournals.org/content/104/4/649.short

http://onlinelibrary.wiley.com/doi/10.1111/j.1095-8339.2009.01014.x/abstract;jsessionid=0DA138B41001148A2DAE530D324EF71E.d04t04?deniedAccessCustomisedMessage&userIsAuthenticated=false