Although exhibiting many features associated with eukaryotic plantae

Although exhibiting many features associated with eukaryotic
plantae such as being non-motile and eukaryotic; Fungi is its own kingdom away
from Animalia and Plantae. This kingdom includes single cellular yeasts to multicellular
moulds and mushrooms in originally four now five phyla; Ascomycota,
Basidomycota, Zygomycota, Chitridiomycota and most recently Glomeromycota1. These
five phyla include all 5.1 million species of fungi in both aquatic and
terrestrial environments.   


Fungi were once considered to be of the plantae kingdom as
they evolve out of soil, require the basic needs of a plants such as water and
exhibit rigid cell walls similar to those of plants. However, one of the main
difference between Fungi and Plantae is that they lack chloroplasts and
chlorophyll thus lack the ability to photosynthesise and produce their own food
source. As a result of this Fungi must absorb their nutrients from either
living of dead material as either a saprophytic, parasitic or mutualistic
absorber. Saprophytic Fungi absorb essential nutrients form dead materials of
either plants of animals. Parasitic fungi get their nutrients from living hosts
and grow on live trees and large plants enabling them to absorb nutrients
already taken up by the host. Mutualistic fungi are similar in the way that
they absorb nutrients from a host however, in this case they reciprocate with the
host and benefit the host in some way. Although plants also absorbs some
nutrients from the soil and some may be parasitic such as the Viscum album2
known as the common mistletoe, the key difference is that Fungi cannot
photosynthesise. All plants have several cells types that contain chloroplasts
and chlorophyll which enables them to convert sunlight into energy and biomass
as autotrophs . Contrastingly, Fungi are heterotrophic and rely on the
inorganic nutrients they take in from dead matter, soil or a host. The adsorption
and digestion of materials in these organisms has always been something that
has defined the Fungi’s differences from plants and similarities to animals.
For example, some Fungi have a short period of time where they must digestion
foods through phagocytosis. This method of feeding is also seen in protists and
some worms in the Animalia kingdom, again suggesting another reason as to why
mushrooms, moulds and yeasts have been liked less to seemingly similar relative
Plantae and more likely to animals.

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Related to the taking in of food materials is the slight
difference between the roots system of vascular plants and the hyphae system of
mushrooms. Hyphae are characterised as long fibrous filaments that collectively
make up the mycelium of the fungus, these hyphae systems can be septate (where
each hyphae branch is divided in separate cells using walls called septa) or
aseptate (where the branches remain clear of walls). The hyphae system of the
fungus lacks a “main root” unlike the root system of vascular plants that tend
to have a main anchor root with several branches off of the main root3
(see figure 1 and 2). There is some speculation as to why this difference has evolved
but it may be partly due to the fact that hyphae lack the root hairs that
appear on the roots of vascular plants. Due to this, hyphae have evolved to
become long an fibrous in order to cover more surface area of the soil and be
able to absorb as much water and nutrients as possible. Additionally, another
reason to this is that some fungi have developed hyphae that are able to be
inserted into the body of their hosts as opposed to just in soil. Thus
suggesting that their hyphae system must be strong enough to insert into the
host but also small enough to enter the vascular tissues in plantae hosts
without damaging them4.





Another key difference between the Plantae and Fungi kingdom
is that plant cellular walls are composed of cellulose; a polysaccharide of
linear glucose7
units but fungi cell walls are composed of chitin; a polysaccharide of
N-acetylglucosamine which is also found in the exoskeleton of arthropods8. This
key physical difference between plants and fungi suggests that the kingdoms are
further away from each other in evolutionary terms than first thought. The similarity
between the cell walls of fungi and the exoskeleton of Arthropods suggests that
Animalia and Fungi have a closer evolutionary relative than that between plants
and fungi. As shown in the figure below9 it
is likely that there was a multicellular heterotrophic protest relative that
links the kingdoms of Animalia and fungi. Before the evolutionary development of
heterotrophs there would have been a autotrophic ancestor which then evolved
into early plants such as Charophytes.




Although Figure 1 shows that animals and fungi are more closely
related than to plants we can also see through genetic screening and evolutionary
trees that all three kingdoms would have shared a common single celled protist ancestor.
Additionally, we can see how heterotrophs evolved from autotrophs as they rely
of the nutrients and biomass produced by autotrophic producers thus again
showing that fungi and animals would have evolved away from plants. Furthermore,
the genetic sequences of fungal ancestors show a clear homology between animals
and fungi. A gene sequence from Dictyostelium, a unicellular slime mould, “show
with statistical confidence that Dictyostelium is closely related to the
animal-fungi clade and is distantly related to plantae”(Kuma 1995)10.


In conclusion, it is evident from the both physical and
genetic differences that the kingdoms fungi and plantae are separate. Although
there are some physical similarities we can be sure when using genetic
screening and evolutionary trees that the kingdom Animalia has a closer living
relative to fungi than plants do. These physical similarities have evolved by chance
through the evolution of an autotrophic protist ancestor to give way to heterotrophs
which are both seen in Fungi and Animalia.


(2017)INTERNET[email protected]/major-fungi-phyla

2 KewScience.

3 Brundrett,M. Working with Mycorrhizas in
Forestry and Agriculture (1996)INTERNET

4 Brundrett,M. Working
with Mycorrhizas in Forestry and Agriculture (1996)INTERNET

5 N/A

6 The
Lichfield Plater Company INTERNET

7 Sagan,

8 Biology

9 Mader,
S (2012) Biology. 10th Edition

10 Melnikova,
M. Nazzaruolo, B. Xie, H (1997) INTERNET