The Largest Mistletoe

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When we think of mistletoes, we generally think about those epiphytic parasites living on branches way up in the canopy. The mistletoe we are discussing in this post, however, is a decent sized tree. Nuytsia floribunda is a native of western Australia where it is known locally as moojar or the Christmas tree. To the best of our knowledge, it is the largest mistletoe known to science.

Nuytsia floribunda is a member of the so-called showy mistletoe family (Loranthaceae). It along with all of its mistletoe cousins reside in the order Santalales but from a phylogenetic standpoint, the family Loranthaceae is considered sister to all other mistletoes. This has excited my botanists as it allows us a chance to better understand how parasitism may have evolved in this group as a whole.

Speaking of parasitism, there are some incredible things going on with N. floribunda that are worth talking about. For starters, it is not fully parasitic but rather hemiparasitic. As you can tell by looking at the tree decked out in a full canopy of leaves, N. floribunda is entirely capable of photosynthesizing on its own. In fact, experts feel that it is fully capable of meeting all of its own carbohydrate needs. Instead, it parasitizes other plants in order to acquire water and minerals. How it manages this is remarkable to say the least.

Nuytsia floribunda is a root parasite. Its own roots fan out into the surrounding soil looking for other roots to parasitize. Amazingly, exploratory roots of individual N. floribunda have been found upwards of 110 meters (360 ft.) or more away from the tree. When N. floribunda do find a suitable host root, something incredible happens. It begins to form specialized roots called “haustoria”, which to form a collar-like structure around the host’s roots.

Whole haustoria of Nuytsia (white [ha]) and host root (dark brown). * indicates `gland' and developing `cutting device.

Whole haustoria of Nuytsia (white [ha]) and host root (dark brown). * indicates `gland' and developing `cutting device.

The collar gradually swells and a small horn forms on the inside of the haustoria. Swelling of the haustoria is the result of an influx of water and as the pressure around the host root builds, the haustorial horn of N. floribunda physically cuts into its victim. Once this cut is formed, the haustoria form balloon-like outgrowths which intrude into the xylem tissues of the host root, thus forming the connection that allows N. floribunda to start stealing the water and minerals it needs.

Even more amazing is the fact that roots aren’t the only thing that N. floribunda will attempt to exploit. Many inanimate objects have been found wrapped up in a haustorial embrace including dead twigs, rocks, fertilizer granuals, and even electric cables! Its non-selective parasitic nature appears to have left it open to exploring other, albeit dead end options. I don’t want to paint the picture that this tree as the enemy of surrounding vegetation. It is worth noting that N. floribunda extracts very little from any given host so its impact is spread out among the surrounding vegetation, making its overall impact on host plants minimal most of the time.

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Provided its needs have been met, N. floribunda puts on one heck of a show around December. In fact, the timing of its blooms is the reason it earned the common name of Christmas tree. Flowering for this species is not a modest affair. Each tree is capable of producing multiple meter-long inflorescences decked out in sprays of bright orange to yellow flowers. The flowers themselves produce copious amounts of pollen and nectar, making it an important food source for resident pollinators. Though many different species have been documented visiting the flowers, it is thought that beetles and wasps are the most effective at pollination.

Seed dispersal for N. floribunda is mainly via wind. Each fruit is adorned with three prominent wings. After they detach from the tree, the fruits usually break apart into three samaras, each with its own wing. The key for success of any propagule is ending up in a site suitable for germination. According to some, this can be a bit tricky and attempts at cultivating this plant in captivity have not been terribly successful. It would seem that nature knows best when it comes to reproductive success in N. floribunda. It may be worth trying to figure it out though because recent evidence suggests that this species is not faring well with human development. As the surrounding landscapes of western Australia become more and more urbanized, plants like N. floribunda seem to be on the decline. Perhaps renewed interest in growing this species could change the tide for it as well as others.

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Photo Credits: [1] [2] [3] [4] [5]

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

Buffalonut - A Parasitic Shrub From Appalachia

I have a hard time with shrubby species. They just don't stand out to me like herbaceous plants or giant trees. As such, my identification skills for this group of medium-sized woody plants are subpar. However, every once in a while I find something that I can't let go. Usually its a species with a trait that really stands out. This is how I came to know buffalo nut (Pyrularia pubera). Its unique inflorescence was like nothing I had ever encountered before. 

There is good reason for my unfamiliarity with this species. It is largely restricted to the core of the Appalachian Mountains, although there are records of it growing on Long Island as well. Regardless, it is not a species I grew up around. The first time I saw its flowers I was stumped. I simply couldn't place it. Luckily its unique appearance made it easy to track down. I was happy with buffalo nut for the time being but I was surprised yet again when I sat down for a chat with someone who knows woody species much better than I do. 

As it turns out, buffalo nut belongs to the sandalwood family, Santalaceae. This makes it a distant cousin of the mistletoes. Like most members of this family, buffalo nut lives a parasitic lifestyle. Although it is fully capable of photosynthesis and "normal" root behavior, under natural conditions, it parasitizes the roots of other tree species. It doesn't really seem to have a preference either. Over 60 different species hailing from 31 different families have been recorded as hosts. 

When a buffalo nut seed germinates, it starts by throwing down a taproot. Once the taproot reaches a certain depth, lateral roots are sent out in search of a host. These roots "sniff out" the roots of other species by honing in on root exudates. When a suitable root is found, the buffalo nut root will tap into its host using specialized cells called haustoria. Once connected, it begins stealing water and nutrients. Buffalo nut roots have been known to travel distances of 40 feet in search of a host, which is pretty incredible if you ask me. 

It is easy to look down on parasites. Heck, they are largely maligned as free loaders. This could not be farther from the truth. Parasites are a healthy component of every ecosystem on the planet. They are a yet another player in a system that is constantly changing. What's more, the presence of parasites can actually increase biodiversity in a system by keeping certain species from becoming too dominant. Buffalo nut should not be persecuted. Instead it should be celebrated. It is yet another species that makes the Appalachian Mountain flora so unique. 

Further Reading:
http://bit.ly/1TTyk9u

http://bit.ly/215u5Mg

http://1.usa.gov/215twlJ