Phoradendron leucarpum (better known as P. serotinum)
Oak Mistletoe ranges across most of Florida, except for the southernmost counties, with the southern gap pronounced in the east, so the presence of a large Mistletoe on a small Live Oak literally a stone’s throw from my office in Palm Beach Gardens is surprising. It doesn’t quite belong here. That the species is “natural” on our campus is less likely than a hitchhike from a distant plant nursery. But there’s the plant in all its fruiting glory, so it gets attention now.
Above: Oak with Oak Mistletoe on PBSC campus. Fifty percent of the biomass in this picture is the Mistletoe. Is it contributing sugar to the relationship?
Two native Mistletoes grace the state of Florida. Today’s species, Phoradendron leucarpum, has a checkered history of different definitions by different taxonomists, but long story short, it ranges across much of the southern and south-central U.S. The other, Phoradendron rubrum, Mahogany Mistletoe, is more at home in the Caribbean with a toehold in the southern tip of Florida. Its fruits are reddish. The traditional European speceis Viscum album looks much like our Oak Mistletoe, which is likewise suitable for Happy Holidays smoochin’. (As recently resubstantiated by Mistletoe expert Justin Bieber. KLICK)
[Oh no, I hope this blog does not come up when fans search Google for Justin Bieber. Not much—they would find it among eight million hits. And if they do, that’ll be good for our hit counter. If you found this by looking for Justin, hey, broaden your horizons and learn about nature too.]
Mistletoes are reputedly parasites, taking water and inorganic minerals from the host while conducting their own photosynthesis, but hold the fone! Life is never simple, and here is the fun weird part:
Research has shown Mistletoe to transfer photosynthates (sugars and related compounds) to the host tree. The Mistletoe and the host are trading commodities. The relationship appears in truth to be symbiotic, one of those win-win outcomes so beloved by administrators. A good parasite does not kill its host, and a sophisticated parasite supports its host! (Reminds me of contributions to the Sierra Club by big polluters.)
The points of contact between the Mistletoe and its host are remarkable. The MT makes structures that run along the host bark, like a grass runner running across the surface of the ground. From the “runners” branch rootlike organs sinking into the host. The rootlike stuctures come into intimate internal contact with the host in three tissues regions:
1. The growing tissue of the MT is usually embedded in the growing tissue of the host (the cambium under the bark). Thus they grow together. Nice trick.
2. The water-conducting cells of the MT join the water-conducting cells of the host within the wood using the same connections the host uses for its own cells. That is, the water-theft is immediate and direct as though the two were the same plant. In terms of internal anatomy, they are.
3. Here is the puzzler. The MT “roots” extend also into the sugar-conducting cells of the host in the young bark. This is mildly odd since the MT has in the past been regarded, as we know, mainly as a water-parasite. But, two things: first, to get to the wood, the MT has to pass through the bark anyhow. And, second, we already know that when it comes to sugar, the MT seems to give back rather than just take.
Another oddity is the pattern of host specificity in at least Oak Mistletoe. If you take a broad look at its host species choices it comes across as fairly unpicky, but in portions of its range the species can have favored host species, not always Oaks. This has led mistletoeologist Dr. Job Kuijt to speculate on host-specific races within the broader MT species.
The abundant white berries look tempting, but to people they are poisonous, sometimes fatally. When squashed they turn to viscous glue, hence the family name Viscaceae. They are adapted to cling to any body part of any critter coming into pressure contact with them, and I think the stickiness remains functional after passage through a bird. (More research needed on that. Will use the Muscoy ducks in my yard.)
What a weird name, Mistletoe. But what does it mean? Googling turns up controversy, but the best (IMHO) origin comes from ancient English, as explained in detail in my good old desktop dictionary, with the “toe” evolving from “tan,” which means twig. The Mistle part is more cryptic and controversial, but a cluster of ancient English-Germanic words resembling “missel” relate to urination. This leads to loose translations of the name as “dung twig,” referring to the way the gummy seeds are deposited on host twigs via birds, including the European “Mistle Thrush,” aka appropriately Turdus viscivorus, the second word meaning mistletoe-eater.