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Pyrularia pubera

Pyrularia pubera

Our spring visit to the North Carolina Arboretum was rewarding, as the institution has a number of delightful areas (not the least of which was an opportunity to visit their research greenhouses). The visit started with a walk through some of the surrounding native forest, which included this shrub. Not particularly showy, I don't think too many people on the trip photographed it, but decided to (it had a label!). I'm glad I did, as it turns out to have some interesting botanical qualities--like the comparison that can be made between it and cobra venom.

There is an exceptional fact sheet about this species written by Dr. Kim Coder for the University of Georgia's Warnell School of Forestry and Natural Resources: Pyrularia pubera (PDF). Much of the information in today's entry is summarized from that work, but if you get interested in the species, I recommend you read his original text.

Pyrularia pubera has several common names; the ones you are likely to find online are buffalo-nut, elk-nut or oil nut. Dr. Coder has listed a few additional ones, including crazy nut and mother-in-law nut. The fruit outwardly resembles a small pear (hence Pyrularia--a small pear (Pyrus)), but the internal development in the fruit of a single pit classifies the fruit as a drupe, much like a cherry or plum. Safe, or at least tolerated, for ingestion by many animals, the fruit is triply poisonous or toxic to humans. Acrid oils in the fruit may cause mouth irritation while calcium oxalate crystals are known to numb tissue (and in high doses, cause death). As for the third, I'll quote from Dr. Coder's report:

"A unique component of Pyrularia pubera is the presence of five different animal-like toxins in its tissues, especially concentrated in the fruit. The shrub contains purothionin, viscotoxin, phoratoxin, crambim, and thionin. A number of these toxins are shared with other sandalwood family members like the mistletoes. Thionin is a small protein which has been proven to be hemolytic (blood), cytotoxic (cells), and neurotoxic (nerves). Thionin attacks membranes in humans (causing them to be leaky) and red blood cells (destroying them.) Thionin can attack heart muscles. It shares the same form of damage and the same binding site within animal cells as does cobra venom, even though it is not similar chemically."

A small shrub growing to 4.5m (15 ft.) tall, Pyrularia pubera is native to dry and moist Appalachian forests from Pennsylvania to Georgia and Alabama. Like all members of the Santalaceae, or sandalwood family, it is a hemiparasitic species (someone correct me if I'm wrong). Pyrularia pubera is a generalist when it comes to parasitism, known to parasitize over 60 species from 50 genera and 31 families, including both woody and herbaceous taxa. Interestingly, one plant of Pyrularia pubera will parasitize another individual of its species, but somehow avoids parasitizing itself.


Safe/tolerated for many animals but toxic for humans? Why the difference?

Wish I was an animal physiologist, but I'm not. The list of animals that thionin (one of the toxic compounds) is apparently toxic to includes humans, pigs and rabbits, while horses, cattle, deer, mice and sheep can tolerate it. Rabbits can apparently manage it in low concentrations, though, as it seems they will eat the bark of the species.

Is this even remotely related to phytolacca, pokeberry? The raceme of unshowy green flowers and the leaves remind me of the pokeberry that grows in my garden where it was sown by a bird and proved too beautiful to pull out. But I have to cut off all of the clusters of inky purple berries in August and discard in the trash or be guaranteed a thousand plants the following year.

They had shared ancestors about 100 million years ago, more or less. That does make them relatively closely related in the grand scheme of things, but that's also a lot of time to diverge.

Thanks, Daniel. They've both kept the trait of toxicity, I see.

I don't know if I would use the word "kept", because something like the accumulation of calcium oxalate crystals has arisen (and I'll guess disappeared) many times in many different plant lineages. It's likely the same case for the toxins, as a quick glance at some sites & databases suggest that they have also evolved in multiple lineages (and again, I'll guess disappeared or inactivated) many times (I'll need to read more on this subject, I guess).

A nasty contrast to one of Australias more famous members of the Santalaceae, Santalum acuminatum or Quandong

That is fascinating and really quite scary!. Great description, it had me on the edge of my seat! :)

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