Feed Me, Seymour!

October 30, 2015

In the spirit of spooky-ness, today I would like to introduce you to some of the most bizarre looking plants on our planet. I am of course talking about the genus Hydnora. Known locally as jakkalskos (jackal food) or bobbejaankos (baboon food), these odd parasites certainly look creepy. However, their ecology is downright fascinating and well worth a closer look.

Hydnora comprises roughly seven species and currently resides in its own family, Hydnoraceae. More recent taxonomic work suggests that this may actually be a subgroup within the family Aristolochiaceae, but as far as I know, the jury is still out on this. All species are native to southern Africa and as you can probably tell from the picture, they produce no leaves and no chlorophyll. Instead of wasting energy on producing its own food, Hydnora has resorted to parasitism. They are root parasites on members of the family Euphorbiaceae. They tap into the roots of their host plants using specialized structures called "haustoria." In this way they are able to gather all their nutritional needs from their host. Once a Hydnora has obtained enough energy it will produce a flower.

The flower is all you will ever see of this plant. The strange, scaly structure emerges from the ground underneath its host. Three slits begin to form, each lined with white, hair-like structures. At first these structures remain intact. The spaces between are just big enough to allow entry of pollinators, which in this case are dung beetles. Once the flower opens these slits it begins to produce some heat, not unlike what we see in many aroids. The heat helps to spread the scent and the smell is what you would expect from a plant trying to attract dung beetles - it smells like feces.

Photo by Charles Stirton licensed under CC BY-NC-ND 2.0

When a dung beetle arrives looking for some fresh poop, it enters the flower through those slits and falls down into the trap. The rest of the flower consists of a tube-like structure underground. To keep the beetles from escaping, Hydnora employs a trick used by many carnivorous pitcher plants. Lining the walls are downward pointing hairs that prevent the beetles from crawling out before their job is done. Once inside, the beetles are drawn to the center where the smell is emitted. Here they are dusted with generous amounts of pollen. If the beetles have arrived after a previous Hydnora visit then they will also deposit pollen and thus reproduction is achieved. Once the plant releases pollen onto the beetles, the hairs lining the wall relax and the slits open completely, allowing the beetles to escape.

I hope some day to see one of these in person. To the best of my knowledge, only a single species (Hydnora africana) has ever been grown in cultivation and that was a single event. Seeds were sown in a pot containing a known host species of Euphorbia. It took a very long time for germination and even longer to mature and produce a flower. Either way this creepy species is actually quite fascinating.

Photo Credit: [1] [2]

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

Itty Bitty Bartonia

September 30, 2015

Every plant enthusiast has a handful of species that they search high and low for any time they find themselves out and about. It may be a species you have seen a bunch of times or one your have only read about in the literature. Either way, the search image burns strong in your mind so that when you finally come across the species in question, it is like seeing a celebrity. For me, one of those species is Bartonia virginica.

It may not look like much. Indeed, it is a rather diminutive plant, barely poking its flowers out of the shadows cast by pretty much every other plant near by. However, when conditions are just right, this little gentian seems to flourish. With leaves that have been reduced to small scales that sheath the dainty stem in a couple places, all that really stands out are the tiny, cream colored flowers that cluster near the top. A close inspection of the flowers with a hand lens reveals the unmistakable morphology that runs true throughout the gentian family.

Whereas the stem of the plant does contain chlorophyll, it has long been suspected that this plant must rely on other means of obtaining carbon due to its highly reduced leaves. A paper published in 2009 by Cameron et al., was able to shed some light on this matter. As it turns out, there is strong evidence in support of B. virginica being partially mycoheterotrophic.

This is such a cool little gentian. I was so happy to have come across some. Sometimes it's not always the biggest or the showiest that make our day, but rather the subtle and unique.

Further Reading:
http://plants.usda.gov/core/profile?symbol=bavi3

http://www.amjbot.org/content/97/8/1272.short

On Parasites and Diversity

September 10, 2015

Photo by Sannse licensed under CC BY-SA 3.0

We all too readily demonize parasites. It is kind of understandable though. The thought of something living in or on you at your expense is enough to make our skin crawl. There are a lot of evolutionary pressures that make us look unfavorably about organisms with such lifestyles. However, to completely write parasites off as a bane to life as we know it may be a huge mistake on our part. More and more we are realizing that parasites play an important role in ecosystem functioning and may even serve as indicators of environmental health.

Plants are no stranger to such parasitic dynamics. Many species have forgone some if not all photosynthetic ability in exchange for a parasitic lifestyle. There is no question that plant parasites can and do have net negative effects on their hosts, however, its never that simple. Research is showing that parasitic plants can have profound effects on the structure and productivity of surrounding plant communities.

For starters, parasitic plants can increase the competitive ability of non-host species. By knocking back the performance of their host, other plant species can pick up the slack so-to-speak. This can often lead to an increase in overall plant diversity in a given habitat. A common thread throughout studies that have looked at parasitic plants is that proportion of grasses declined when parasitic plants were present. This made room for less competitive forbs to increase in number. In effect, parasitic plants can level the playing field for other, less competitive plant species.

By altering ecosystem structure, parasitic plants can also alter the way nutrients flow through the system. This can have some seriously profound ramifications. For instance, the presence of the hemiparasitic Rhinanthus minor in grasslands has been shown to increasing rates of nitrogen cycling. Though the ramifications of this are dynamic, it is nonetheless proof that parasites should not simply be maligned and that, despite our perspective, nature is far more complex than we realize.

Photo Credit: Sannse (Wikimedia Commons)

An Aromatic Parasite

July 9, 2015

What smells like honey and parasitizes fungi? Why, Monotropa hypopitys of course! Its specific epithet gives you an idea of where you may stumble across one of these strange beauties. Hypo means under and pitys means pines. It is no wonder then that the common name of this species is "pinesap."

I love parasitic plants and to find this species was a real excitement. I smelled it before I saw it. The yellowish coloration of this specimen represents the norm, however, individuals with a more reddish hue are not unheard of. Pinesap has a distribution spanning the forests of the northern hemisphere. It is the most widely distributed member of the genus. Despite this fact, stumbling across a population is a relatively rare occurrence.

Pinesap falls under the category of mycoheterotroph. It parasitizes fungi, specifically those in the genus Tricholoma. As such, it is an indirect parasite of trees, taking nutrients that the fungi obtained from the trees they associate with. The relationship between pinesap and its associate fungi are rather specific. The structures they form are so unique that researchers have created a new term just to describe it - 'monotropoid’.

For most of its life, pinesap lives underground as a collection of highly specialized roots. Come early summer, individuals with enough stored energy will throw up what looks like a stem covered in flowers. In actuality, pinesap does not produce anything that could be called a true stem. Instead, the structure we see is actually an inflorescence called a raceme.

As mentioned above, the flowers have a scent that reminds me of spicy honey. Bees are the main visitors of the flowers, though most researchers feel that the plant mainly self pollinates. It has been observed that yellow individuals tend to flower earlier in the summer while red individuals tend to flower closer to fall. Whether this is any indication that these are separate subspecies remains to be seen. Recent genetic analysis suggests that pinesap may very well deserve its on genus, Hypopitys monotropa. More work needs to be done to figure out if it is deserved.