Picking up from my recent post about spring parasites that aren’t mistletoe, here are some pictures of what mistletoe seeds do in spring. And that is, mostly, germinating. On any old surface. As the seeds won’t know, until the seedling tries to attach itself to a host, whether it is sitting on a host or not. Interestingly, for these few weeks of germination, the mistletoe plant is independent, not parasitic, and relies on the resources of the seed, plus a bit of photosynthesis, to survive. If it finds it’s not on a host, it will die.
Here’s a seed I stuck on an internal window frame back in February, photo taken today. It germinated about 2 months ago, with two hypocotyls (two embryos in this seed, not unusual for mistletoe) emerging and now seeking a tree to parasitise. It is, of course, out of luck and doomed. But it has survived three months without even being watered. They are very determined at this stage!
Around the garden there are, probably, hundreds of similarly sprouting seeds, mostly spread by blackcaps from the mistletoe in our apple trees in February. Many are just as doomed as that window frame example above, either because they’re not on a tree, or not on a suitable tree.
As examples of unsuitable hosts the next two pictures show germinating seeds on Spindle Tree, Euonymous europaeus and on Bay, Laurus nobilis. Neither are likely to be viable hosts, but those germinating seeds don’t know it yet.
The most suitable hosts we have are the apple trees which in our garden are (in effect) sacrificed to mistletoe, as I’m more interested in studying the mistletoe than the apples. Some are overdue for mistletoe management as there will, ultimately, be so much it risks the future of both tree and mistletoe. That’s an issue for another post next winter. For now, here are more seedlings (all today’s pictures were taken today, 11th May).
You 
can see, however, from the sheer numbers of germinating seeds, why that control may be needed sometime soon. This pair of pictures shows multiple seedings, from seeds with multiple embryos, clustered together closely.
Note, in the second picture, the two or three year-old seedling standing upright with its first pair of leaves developing.
There are more second and third and probably fourth year seedlings on the next picture, below, too, alongside newly germinating seeds from this spring. You can see how a rash of seedlings can quickly dominate when there are this many seeds about.
Those older seedlings, by themselves, can look very stylish, as with this one just catching the light on its first leaf-pair.
On apple these seedlings will grow very easily, developing the distinctive bifurcating branching pattern that effectively doubles the plant’s size each year. The same applies to many other common hosts, including Limes, Poplars, Willows, Hawthorn etc. But on some other hosts, whilst the parasitic connection is made, the subsequent growth seems stunted. Here are two examples, from the same garden today, but these are mistletoe plants that established several years ago. Both seem very stunted.
The first is on Japanese Quince, Chaenomeles japonica, which can support mistletoe but, in this case, seems to be putting up a fight. The mistletoe here is definitely struggling, with multiple short stunted growths rather than one or two strong growths. The swelling of the host branch shows that the haustorial connection is well-established nevertheless.
The second one is on Wall Cotoneaster, Cotoneaster horizontalis, and seems even more stunted but with an impressively bulging haustorium. Quite how these hosts resist the mistletoe isn’t clear, but it seems something is going on. Either that or, as both the last two examples are on wall-mounted plants, there might be easy access (compared to up a tree) for slugs and snails which might, perhaps, literally be nipping the mistletoe in the bud every season, leaving a remnant, and the haustorium, which re-sprouts, in hope, each year..
The oddest host, for mistletoe, is, er, mistletoe itself. It frequently parasitises itself, quite successfully, and this goes some way to explain why some people report their mistletoe seems to be both male and female, as one is actually growing on the other (other possible causes of this are , of course, male and female seedlings growing up from the same spot). I’ll finish with a couple of examples of newly germinating mistletoe seeds on an existing mistletoe branch, possibly their own parent.
Slide show below:
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