categoryZEvergreen Evergreen List 

MISTLETOE

Viscum album

Bastard-toadflax Family [Santalaceae]

Flowers:
month8feb month8mar month8march month8apr month8april

Berries: berryZpossible        berryZwhite  (poisonous, sticky)
berry8Nov berry8Dec

category
category8Evergreen
status
statusZnative
flower
flower8green
morph
morph8actino
petals
petalsZ4
stem
stem8round
toxicity
toxicityZmedium
sex
sexZdioecious

26th April 2013, Linchmere, nr Haslemere, West Sussex Photo: © Dawn Nelson
On a Poplar Tree host. Not un-like the tree gall Witch's Broom.


26th April 2013, Linchmere, nr Haslemere, West Sussex Photo: © Dawn Nelson
On a Poplar Tree host. Roughly spherical populations up to a metre across and usually at un-reachable heights.


23rd Feb 2016, a tree, Leigh, Lancs. Photo: © RWD
Usually in the shape of a globular cluster with stray braches sticking out around the edges.


20th April 2013, nr. Bletchworth, Surrey. Photo: © Dawn Nelson
Usually so high up in the tree as to be un-reachable except for the long pole used to harvest it for Christmas Yuletide and the kissing underneath thereupon. A branched mass up to a metre across.


20th April 2013, nr. Bletchworth, Surrey. Photo: © Dawn Nelson
Leaves yellowish-green, elliptical and leathery. Usually in pairs.


23rd Feb 2016, a tree, Leigh, Lancs. Photo: © RWD
 At branch junctions are several flowers, two, three or as here in the centre four. Because the plant is dioecious, and the male and female flowers are on separate plants, with this specimen having berries, these must be female flowers.


23rd Feb 2016, a tree, Leigh, Lancs. Photo: © RWD
Berries small, pearly-white, spherical. Highly poisonous! There are four in this photo...


23rd Feb 2016, a tree, Leigh, Lancs. Photo: © RWD
 A very architectural plant: short and dead-straight branches in opposite pairs or in triplets at a characteristic forward angle, branched fractally to end branches which have a pair of opposite leaves shaped rather like aeroplane propellers but often curved slightly forwards.


20th April 2013, nr. Bletchworth, Surrey. Photo: © Dawn Nelson
 It is dioecious, having male and female flowers on separate plants. These are female flowers. They are very stubby, with short yellowish-green tepals (petaloid sepals) and slightly reminiscent of a pigs snout and ears. Here situated at a Y-branching of the stem.


20th April 2013, nr. Bletchworth, Surrey. Photo: © Dawn Nelson
 Female flowers which have a central very stubby style and stigma in the centre, and no pollen on the inside of the tepals.


20th April 2013, nr. Bletchworth, Surrey. Photo: © Dawn Nelson
 Three female flowers. In the centre of each flower is the circular nectary which surrounds the central single stigma.


Photo: © Ann Collier
 The number of berries in a cluster reflects the number of fertilised female flowers, sometimes just on, or two, more often it seems in three's and up to 5 in one cyme. The stems are very jointy, bifurcating at regular intervals. There are some female flowers in this photo which have not been fertilised so have not produced a berry.


Photo: © Ann Collier
 Berries more often it seems in three's arranged as in a pawn-brokers shop sign. The formerly green twigs have turned a dull yellow. It is possible the berries here have growing on them a green algae.


Photo: © Ann Collier
 Berries pearly dull-white, very spherical, semi-glossy and covered in minute pimples/indentations. They look translucent. Pole to pole segmentation is visible as slightly whiter radial lines. A largeish dark pimple is present at the far pole; the remnants of the stigma.


Photo: © Ann Collier
 Male Flower.


Photo: © Ann Collier
 Several clusters of male flowers at the ends of these twigs, with a pair of leaves either side of them.


Photo: © Ann Collier
 This flower cluster has 5 male flowers visible.


Photo: © Ann Collier
 A small cluster of just 2 male flowers terminate this twig.


Photo: © Ann Collier
 2 Male Flowers. The anthers are stuck to the inner surfaces of the 4 tepals, the pollen is lime-green to cream.


Photo: © Ann Collier
 the pollen on the tepals of the male flowers.


Some similarities to : Witches' Broom which is a gall on Birch or Hornbeam and also on Wild Cherry (Gean) trees trees usually caused by the fungus Taphrina betulina which look rather like bird's nests, but they are usually more dense than is Mistletoe.

Uniquely identifiable characteristics

Distinguishing Feature :

Mistletoe is Dioecious, with male and female flowers on separate plants, the sticky white berries only appearing (between November to December) on female plants. The berries are eaten by Mistle Thrush birds as well as by other birds, but they are so sticky that they also stick to the bird's beak as they try to eat them from where they are ready to be implanted on the next high branch of a tree that the bird visits. Because birds prefer to be high up in the trees, Mistletoes is to be mostly found near the top of the tree. But Mistletoe will only take on first or second year tree growth, and even then can take a whole year to 'root' and establish a connection with the host tree before it can obtain nutrients and fluids. Before that first year is up, it is on its own.

Mistletoe is  Hemi-parasitic and grows on, obtaining some nutrients (but not all) from deciduous trees only, especially Malus (Apple) at 40% of mistletoe occurrences, then in descending order of popularity (by the Mistletoe choice itself): Tilia (Lime), Crataegus (Cockspurthorn & Hawthorn), Populus (especially Black Poplar), Salix (Willow), False Acacia and only rarely on Quercus (Oak). But it can grow on virtually any tree, but these are all of much lower probability. It is grown commercially on mainly Apple trees in orchards for the Christmas trade in mistletoe for kissing beneath.

It grows from a seedling by 'gluing' itself to the bark of a tree by means of the sticky viscous liquid they contain. In the first year it will have grown 4 leaves on one branch. It branches into two once a year, the number of branches doubling each year, until it is a globular mass which grows slightly larger every year. In the last 15 years since 2000AD mistletoe seems to be spreading faster than usual. It is capable of photosynthesis itself but draws water and minerals from its host vascular system at distinct swellings or gall where the two conjoin. It looks as though it buries itself under the bark of the tree, but this is incorrect; it grows on the surface of the bark, but initiates the tree to grow bark over and around itself, so that eventually it is growing from a large knob of altered bark tissue (aka haustorium). After gluing itself to the bark, the seedling puts tentacles into the tree by which means it can obtain some nutrients, and especially water, from the tree. Mistletoe does have green leaves, so it is able to generate some of its own nutrients by photosynthesis; but those it cannot it steals from the host tree, especially water.

Out of several sub-species found in the World, only the 'parent' grows in the UK, Viscum album. It contains a toxic protein and lectin called Viscumin which has a high molecular weight. Other sources make mention of viscotoxin as one of the toxins. They are, like Ricin, a RIP, a Ribosome Inactivating plant Protein which is another poisonous lectin, although the two target and bind to differing sites. Although Mistletoe is poisonous, fatalities are rare. The toxin is concentrated in the white berries but is said to be present throughout the whole plant.

Mistletoe does, of course, contain other chemical compounds, but because Mistletoes can grow on a wide variety of differing trees and is hemi-parasitic on them, obtaining some nutrients from them, the composition and proportions of these secondary metabolites varies. However, any toxicity of these compounds will probably pale into insignificance compared to the toxicity of the viscotoxins. A new acyclic monoterpene diglycoside has been found in Mistletoe, but it lacks a common name and the chemical name is very long.

Its greatest population density in the UK is in Somerset and Devon with a very broad spread around the home counties and a smaller outbreak on the Mid-Wales border. Virtually no presence north of South Yorkshire apart from one or two hectads. It grows mainly in gardens and orchards with a lot of parkland presence also. Roads, hedgerows, fields and woods taken together account for just 20% of the population.

MITOCHONDRIA and ATP IN PLANTS

It was once thought that all plants (multicellular eukaryotes) use mitochondria to generate energy until early 2018, when scientists were astonished to find an exception to this: Mistletoe! The parasitic character of Mistletoe has somehow enabled it to lose much of the functionality within the mitochondria (which it still possesses, but in abnormal form). 'Use it or lose it', as the saying goes. But in the case of Mistletoe, unlike many other parasitic plants, it has lost it! Mistletoe has much less need to generate energy using ATP in mitochondria because it obtains nearly all of its energy needs from the host tree upon which it is parasitic. And now, it can't, although scientists do not know when it lost most of this ability, but it is likely to be thousands of years ago in the annals of prehistory.

Mitochondria are present in all other multicellular eukaryotes, which includes plants and animals (humans too). [Mitochondria are absent or low in single-celled eukaryotes, such as yeasts]. All normally rely on mitochondria and the ATP (Adenoside TriPhosphate) within them to generate and convey the energy which they require. This is a complex process involving many enzymes and complexes, named Complex I to Complex V.

In Mistletoe it was first thought that they had lost the genes required to synthesize the subunits of Complex I, or that the genes required may have been transferred from the mitochondrial DNA to the nuclear DNA. But it is now thought that (European) Mistletoe completely lacks Complex I and that the genes encoding for the subunits of Complex I are completely absent from Mistletoe. Not only that, but it also has greatly reduced amounts of Complex II and Complex V. Moreover, Complex III and Complex IV have, in Mistletoe, have formed SuperComplexes, which are remarkably stable and involved in respiration. Mistletoes entire repiratory chain has been completely overhauled and remodelled. The levels of Complex IV (and the enzyme which synthesises ATP) are present in amounts 5 times lower than that of another 'commonly studied laboratory plant' (possibly meaning Thale Cress - your Author). But the presence of other essential metabolic enzymes were measured at higher levels. These findings illustrate that the mitochondrial functions within Mistletoe have undergone extreme alterations over their evolutionary timeframe.

Because Mistletoe obtains nutrients from it's host trees it seems that it has now lost the ability to generate much ATP within mitochondria. Mistletoe is now far more reliant on its host to obtain ATP, synthesizing but 25% of what its capacity would be if all were intact, although there is still the possibility it may generate ATP in other cellular components. For instance, cells might pick up part of the shortfall by using sugar to generate ATP by glycolysis; although this pathway is 12-fold less efficient than by the normal way of synthesizing ATP within normal mitochondria. Mistletoe may save energy overall though by stealing the sugars from its host. More research is obviously required.



The green parts are the TriPhosphate part. The blue is the Adenine base whilst the red is the sugar moiety, in this case Ribose which is a pentose sugar - the same sugar as occurs in RNA being short for RiboNucleic Acid. When giving up the energy stored in this ATP molecule the triphosphate becomes first ADP (Adenosine DiPhosphate) then AMP (Adenosine MonoPhospate). ATP is both the precursor molecule to both RNA and DNA (DeoxyriboNucleic Acid).

ATP is the energy source for a great many biological processes and chemical reactions in both plants and animals. It is used by cells as a coenzyme. ATP has a great many functions in cells; synthesizing macromolecules such as proteins, RNA and DNA, and in the transportation of macromolecules through cell membranes, both into or out of the cell.

It has been found that normal cells (not those of Mistletoe) contain far more ATP than these processes actually require - 5 times more in fact. This might be because ATP is also used in other ways - it can make proteins soluble and serve as a signalling molecule. As an amphiphilic molecule it has characteristics of both a hydrophilic and hydrophobic substance, but does not assemble itself into films such as micelles.


  Viscum album  ⇐ Global Aspect ⇒ Santalaceae  

Distribution
 family8Bastard-toadflax family8Santalaceae

 BSBI maps
genus8Viscum
Viscum
(Mistletoe)

MISTLETOE

Viscum album

Bastard-toadflax Family [Santalaceae]