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Old 03-04-2019, 12:13 PM
 
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[quote=Aredhel;54567852]This summary from Wikipedia provides a useful overview of the difficulties of modern taxometry: https://en.wikipedia.org/wiki/Taxonomy_(biology)

Basically, step 1 in classifying an organism is to answer the question: does the organism's cell/cells possess a nucleus? If yes, it's a eukaryote. If no, it's a prokaryote.

If the organism is a prokaryote, the next step is to determine whether it should be classified as a bacteria or an archea (this is determined by looking at the organisms ribosomal RNA genes, which are strikingly different between these two groups of organisms).

If the organism is a eukaryote, the next questions to ask are whether it's a heterotroph or photosynthetic, and whether it's single-celled or multicellular.

Multicellular, hetrotrophic, cells lack a rigid cell wall = animal

Multicellular or unicellular, heterotrophic, cells possess a rigid cell wall containing chitin = fungus

Multicellular or unicellular, photosynthetic, cells possess chloroplasts containing chlorophyll b, cells have a rigid cell wall containing cellulose = plant

Unicellular, hetrotrophic, cells lack a rigid cell wall = protozoan

Unicellular, photosynthetic, cells possess chloroplasts containing chlorophyll c = chromista

(The unicellular organisms are the toughest to clearly classify.)

Indian Pipe is no longer photosynthetic, but because it is multicellular, possesses rigid cell walls composed of cellulose, and has flowers, we know it once possessed chloroplasts but lost them when it adapted to parasitism as the means of its survival. That's why it's still classified as a (very odd) angiosperm plant.

Edited to add: It's similar to the reasoning of why whales and dolphins can still be classified as mammals despite being hairless. While they no longer possess hair, having lost it during the evolutionary adaptation to a fully aquatic life, they still possess all the other essential traits of class Mammalia: specialized milk glands for feeding their young, a middle ear with three bones (present during fetal development; this may be lost, depending on the species, by adulthood), and a brain possessing a neocortex. Likewise, a hypothetical bipedal animal with naked skin but possessing a toothless beak composed of keratin, a pygostyle instead of a long, bony tail, a keeled sternum and fused clavicles, and a respiratory system with air sacs plus lungs that provides a one-way flow of air through the lungs has to be a bird. Feathers aren't the only trait that is unique to avians, and the one-way lung structure in particular evolved only once (in the therapod dinosaur lineage from which modern birds arose).

Classification is never based on solely one trait.[/quote]




Right - which is why I was asking what are the criteria that make it a plant (rather than, for example, its own stand alone category). And of course, that definition of plant above is not correct - as it excludes... Indian pipe.
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Old 03-04-2019, 12:15 PM
 
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Originally Posted by luv4horses View Post
This is a good answer. Parasitic plants have lost some critical biochemical pathway that makes them dependent on a physical connection to another plant species that “feeds” it. Sometimes the plant parasite is attached to another plants roots and you don’t see the connection. Sometimes attachment is to tree tops. Occasionally fungi supply what is missing or at least inadequate. And yes mushrooms are plants. They just don’t make sugars using sun energy
That's not correct.
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Old Today, 07:10 AM
 
Location: Omaha, Nebraska
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Originally Posted by Chint View Post
Right - which is why I was asking what are the criteria that make it a plant (rather than, for example, its own stand alone category).
And you’ve received your answer. Indian Pipe cannot be placed in its own kingdom becuuse it possesses two traits that only evolved once (cellulose cell wall and flowers) and which clearly show its evolutionary descent from angiosperm plants. As a direct descendent of an angiosperm plant, it is a member of the clade of angiosperm plants; it can be given its own lower categories (class, order, genus, species), but not its own higher ones. Ultimately the classification system is about delineating evolutionary relationships (and specifically lines of descent). Since Indian Pipe is an evolutionary descendent of an angiosperm plant, it has to remain in the kingdom Plante if its correct evolutionary relationship with other living organisms isn’t going to be obscured.
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Old Today, 08:32 AM
 
Location: Omaha, Nebraska
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Originally Posted by Chint View Post
We don't have the genetic history of the plant - its all inference based on its current structure.
This brings up an interesting point, btw. The basic Linnean system used to classify organisms predates evolutionary theory - and it also predates our ability to sequence DNA. We couldn't sequence large stretches of DNA until the 1980s (when I was in graduate school working in a molecular biology laboratory). This was a golden opportunity to do what Creationists say can't be done: completely disprove the theory of evolution. Evolutionay theory implies that the more closely related two organisms are, the more similar their DNA should be. If it had turned out that DNA sequencing showed that our DNA was more similar to the DNA of horses than of chimpanzees, the DNA of an oak tree resembled the DNA of a salmon more than the DNA of a beech tree, the DNA of a crocodile was closer to the DNA of a mushroom than an alligator, etc., the whole theory of evolution would have been completely disproved. Instead, DNA sequencing showed that by and large we got the classification system (originally developed solely based on morphological similarities) right. We've rearranged a few minor branches on the Tree of Life based on new evidence provided by DNA sequencing, but on the whole DNA sequencing just added more proof that the Theory of Evolution is actually true.

Think of that the next time you hear some crackpot saying that the Theory of Evolution can't be disproved, so it's not a real scientific theory! It passed a huge test with flying colors back in the 1980s/1990s, one that simply couldn't have been carried out at the time Charles Darwin proposed his theory.
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