The horse chestnut belongs to the domain Eukarya because of its evolutionary and morphological relationships with other Eukaryotes.  The other two domains are the Bacteria and the Archaea, both defined as prokaryotic.  In comparison to Prokaryotes, each defining cell in a eukaryotic organism contains membrane bound organelles, such as the mitochondria andchloroplasts.  The chromosomes of this plant are many and are linear instead of single and circular.  Also, the cellulose in the cell walls of this plant is distinguished from the Bacteria and Archaea cell walls. 

SUPERGROUP- Archeaplastida
    The main characteristic that all members of the Archeaplastida share is their primary method of obtaining nutrients, photosynthesis.  However, by no means are the Archeaplastida the only organisms with this ability.  Organisms within this supergroup vary in size, reproduction methods, color, shape, and habitat.  Other than the land plants, this phylogenetic group contains the red algae and the green algae. 

KINGDOM- Plantae
    The horse chestnut and all of the other members of this kingdom share a common ancestor.  This ancestor is thought to have closely resembled a group of green algae coined the Charophytes.  One major piece of evidence that points to this conclusion is the pigments found within Charophytes.  Out of all protists, only the green algae contains chlorophyll a, chlorophyll b, and carotenoids; the pigments contained by most plants.  As far as reproduction is concerned, this group of green algae and plants both exhibit alternation of generations.  These two groups of organisms also share similar cell walls, peroxisomes, and rRNA sequencing data.  For another ortanism in the Plant Kingdom visit Maryam Alhumaidi.

    The Tracheobionta is a super division that contains all vascular plants, including the horse chestnut.  Vascular plants contain specialized transport vessels that move water, nutrients, and sugars throughout the plant.  This super division also includes all of the flowering plants, the conifers, the ginkgos, the cycads, and a group called the Gnetophyta.  Some examples of plants that lack this vascular tissue are true mosses, liverworts, hornworts, club mosses, and ferns. 

SUPERDIVISION- Spermatophyta
    This division encompasses all vascular plants which also produce true seeds.  These seeds contain an embryo, stored food, and a protective seed coat.  This evolutionary step gave plants of this division a large advantage over the spores of non-seed plants.  The embryo gains immense protection from the seed coat and the stored food allows for better chance of survival.  Consequently with the development of the seed, all members of the Spermatophyta are heterosporous.  This means that they have both a male and female gametophyte to independently produce sperm and eggs. 

PHYLUM- Magnoliophyta
    Sometimes known as Angiosperms, this phylum includes flowering plants.  The major defining characteristic of this phylogenetic group is its distinct reproduction.  As breifly mentioned, all organisms within this phylum have a specialized method for transferring pollen called flowers.  These are aesthetically modified leaves which aid in pollen transfer and reproduction in general.  Fruits are also very common in this group as they help to protect the seeds and embryos.  The horse chestnuts spiny fruit is a great example of providing intense protection of the embryo.  Also in the reproduction of these organisms, two sperm cells unite with the 2 polar nuclei in the female gametophyte.  This is the only phylum of plants which contain the process just explained termed double fertilization. 

    The phylum Magnoliophyta is split into three classes, Magniolopsida (or eudicotyledones), Liliopsida (or monocodyledones) and Magnoliids.  The terms listed in parenthesis come from the number of cotyledons in the seeds.  Monocodyledones only have one and eudicotyledones have two.  If the seed is not available for examination there are luckily many obvious distinguishing factors between these two classes.  Eudicotyledones like the horse chestnut have flower groups in multiples of 4/5s, secondary growth, vascular bundles in a ring formation, and net-shaped leaf venation.  Monocodyledones on the other hand have flower groups in multiples of 3s, no secondary growth, randomly placed vascular bundles, and parallel leaf venation.  To read about another organisms that is part of this class visit Passion Fruit.

ORDER- Sapindales
    The stereotypical organism in this order would be a woody plant with compound leaves and dioecious flowers.  Other families in this order are Rutaceae, Meliaceae, Simarougaceae, Anacardiaceae, Burseraceae, Kiracaea, Aceraceae, Biebersteiniaceae, and Nitrariaceae.  The grouping together of these seemingly very diverse families was completed through the use of DNA data, morphological characteristics and chemistry.  Even so, there is still dispute on the organisms that should be included in this order. 

FAMILY- Hippocastanaceae
    There is little dispute as to whether the Aesculus hippocastanum should belong to this family however as it is often referred to simply as the horse chestnuts.  This family consists of deciduous trees with palmately compound leaves and an inflorescence.  An inflorescence is a cluster of flowers that come directly from the stem of the plant.  This, in a large part is what allows for such aesthetic looking trees. 

GENUS- Aesculus
    This family consists of deciduous trees and shrubs that exist all throughout the Northern Hemisphere.  This genus only includes nineteen species in total but have been cultivated at large for medicinal purposes.  Outside of these nineteen species there are 8 documented official hybrids within this genus.  There are two main types of these trees and shrubs; the species native to North America and the species native to Eurasia.  The common names of most of the other members of this genus are the texas buckeye, the california buckeye, the chinese horse chestnut, wilson's horse chestnut, the yellow buckeye, the ohio buckeye, the indian horse chestnut, the dwarf buckeye, the bottebrush buckeye, the red buckeye, the painted buckeye, and the japenese horse chestnut. 

Aesculus hippocastanum

The prefix hippo- appropriately translates from the Greek to mean "horse."  The reason this tree is named after the horse is a topic of debate, but a common explanation is shown in the cover photo above.  The leaf scar on the   horse chestnut tree very closely resembles a horseshoe.  The end of the species name, -castanum , is a reference to its close resemblance to true chestnut trees, members of the genus Castanea.

The phylogenetic tree above portrays the relationships between the species within the Aesculus genus.  This image was recreated by me from a report published in the Jornal of Systematics and Evolution titled "Estimating ancestral distributions of lineages with uncertain sister groups; a statistical approach to Dispersal-Vicariance Analysis and a case using Aesculus (Sapindaceae) including fossils."  This specific tree was created using "phylogenetic analysis" of the extant species and wild card fossils and their distribution.  Following is an additional phylogenetic tree showing the relationship between plants and other organisms.  This tree was created based on RNA data and was compiled by Carl Woese.  Many of these relationships are debated, but this offers an overall review of what some genetic evidence suggests.
If you would like to explore the phylogenies of other organisms visit Beluga sturgeon and Litchi chinensis!

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