Humans

History: Willow Bark particularly from the White willow tree has been used since 400 BC during the time of Hippocrates, who was a famous Greek physician at the time. The willow tree is native to Europe, Asia and regions or North America depending on the species, the white willow is native to Europe.

 

Reproduction: a white willow is an angiosperm meaning it is a flowering plant. In order to reproduce the tree mostly relies on the wind for pollination rather than relying on insets or animals. The flowers of a Willow tree are contained in Catkins a dense cylindrical structure containing clusters of flowers. The white willow is a dioeciously meaning each flower has only one sex, male or female. This means that the tree relies purely on sexual reproduction in order to pollinate. Sexual reproduction allows for cross-pollination and a more diverse species. The male flower has tubes called anthers, which holds millions of diploid microsporocytes, which divide by meiosis and produce haploid microspores. Within the female plant, which consists of carpels, made up of stigma, style, ovary and ovule there is a single diploid megasporocyte, which divides into 4 haploid megaspores, only one of which survive. Because the plant does not have both megaspores and microspores it is not considered hetrosporous, which most angiosperms are. From here the microspores go through differentiation and mitotic division to produce a male haploid gametophyte referred to as a microgametophyte or pollen grain. The megaspore undergoes mitosis and produces 7 haploid cells, which are called the megagametophyte consisting of an egg and 2 polar nuclei. When pollination occurs the pollen grain pollinates the female part of the plant by landing on the stigma the pollen tube grows down the style until it meets the female gametophyte. From her 2 sperms from the male pollen grain travels through the tube where one fertilizes the egg creating a diploid cell (2n) and the other fertilizes the polar nuclei creating a triploid cell (3n). This is referred to as double fertilization. The zygote then develops into an embryo and the triploid cell develops into the nutritive endosperm of the seed. When the sporophyte matures the life cycle begins again (Salix Alba White Willow, n.d) (Biology 11, 2011). 

 

Physical Description: The Bark of a willow tree is normally greyish or brown with a smooth texture. The leaf of a willow tree is long and oval shaped and always has short teeth along the edges as shown below. The leaf has net like veins indicating it is a dicot rather than a monocot.  A willow tree has dry fruit and the seeds are silky and plump. The willow has 2 leaf type structures at the base of the leaf stock often shaped like ears called stipules, they act as the base of the leaf and often grow under it, there is no knowledge to if these stipules are photosynthetic or not. The willow tree also poses flowers called catkins that are cone shaped structures that stand upright on the branch of the willow normally right before or with the leaf of the tree. The female catkins are yellowish/greenish in colour and the male catkins have bright yellow and sometimes purple anthers. Each catkin has black speckles on its hair, which have a silky hair like texture. The stem of the willow tree is woody, in order to grow bark the willow has a cork cambium and vascular cambium allowing the tree to grow wider. The tree only grows in the summer and the age can be seen with the number of rings within the trees stem/trunk. Because the willow is woody it has vessel elements (a vascular tissue found in xylem), which allows for water conduction through the plant. The root system of the willow tree contain 4 layers, the epidermis which is a thin layer of cells with root hairs to absorb minerals, water and increase surface area. The second layer is the cortex in which water passes through cells via osmosis to the vascular cylinder. The third layer is the endodermis, which surrounds the vascular cylinder. It also has a waxy coating around it called the casperian strip. The final inner layer of the roots is the vascular system that contains the xylem and phloem. Water moves through the roots when the root pressure builds up through osmosis, this process pushes the water up and to the rest of the pant.Because the willow is a dicot it has vascular bundles only around the perimeter of the stem/trunk of the tree. As for the formation of the root system dicots grow deeper than monocots having one primary root and with secondary roots branching off (Salix alba L, n.d) (Biology 11, 2011). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Current/ past medical usage: In the past people in place such as Europe and China used Willow Bark for centuries to treat fever and inflammation. During this time they would have patients chew on the bark to treat their symptoms. This remedy is still in fact used today to treat pain related illnesses such as Osteoarthritis and back pain. Many years later it was found that the White Willow Bark in particular contains the chemical salicin, similar to the chemical acetylsalicylic more commonly known as aspirin. Salicin is also responsible for the creation of aspirin in the 1800’s. The chemical is said to have anti inflammation and pain properties, however in recent studies it shows that the chemicals polyphenols and flavonoids have fever reducing, immune boosting properties along with antioxidants and is antiseptic. Studies have also shown that white willow bark in particular is just as good if not better at reducing inflammation and pain than aspirin and can be used in smaller doses. However, it does not help reduce fever. Willow bark can be used as a dry herb to make tea, it can be bought as a powdered herb in a capsule or as a tincture (a type of alcohol). Side effects of willow bark include nausea, vomiting, stomach inflammation, ulcers and stomach bleeding. All of which are side effects of all compounds containing salicylates. Overdoses can cause kidney inflammation, a skin rash, vomiting and tinnitus (a ringing in the ear). It is not recommended to pregnant or breastfeeding women and can also lower or interact negatively with other prescription drugs such as beta-blockers and blood thinning medications. A doctor should be consulted when dosing willow bark and precautions should be taken (Willow Bark, n.d).

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