Domain Eucarya or Superkindgom Eukaryota
Kingdom Plantae

At the top of Carolus Linnaeus's original system of classification were two kingdoms, representing plants and animals. The plant kingdom has been revised a bit since then, but there are still distinguishing characteristics that cause biologists to group all plant species together.

  • Plant cells contain chloroplasts filled with chlorophyll, which they use to make their own food via photosynthesis.
  • Plant cells have cellulose cell walls
  • Most plants require being anchored to a surface of some sort: the ground, the sea bottom, or another plant.
  • Plants reproduce sexually, but in a peculiar way called "alternation of generations" (Follow the link, because I put a lot of work into that one).

Plants appeared during the Ordovician Period (after animals), and were the first living organisms to colonize the land. Paleozoic forests were dominated by giant horsetails; ferns evolved into cycads, which evolved into conifers, and finally, by the Cretaceous, the flowering plants which dominate the kingdom today.

Plants have been classified morphologically, cladistically, and even by height. Because of this, primary divisions (preferred to "phylum" in modern classification) of Plantae can have several names.

The most closely related organisms to plants are members of the Kingdom Chromista, or "algae", particularly the Chlorophyta ("green algae") and Charophyta (stoneworts). Many Chromista are auotrophic via photosynthesis, can reproduce sexually, and some even alternate generations as plants do. In other types of Chromista, cells contain a different type of chlorophyll and do not store energy as starch. Because the Charophyta and Chlorophyta use chlorophyll a and b, but are structurally and genetically similar to other algae, it is difficult to place these two groups in a kingdom. Thus, some plant classifications contain the Charophyta and Chlorophyta. But many classifications do not include them, and restrict kingdom Plantae to land plants.

Since the gametophyte-dominant plants and the sporophyte-dominant plants probably evolved from different algal ancestors, "Plantae" is probably polyphyletic unless the two groups above are included.

  • Non-vascular plants are (24,000 species) are dominated by the gametophyte generation. The "plant" you see most of the time is the gametophyte, and the sporophyte ("fruiting body") is usually parasitic on the gametophyte which produced it. After dispersing their spores, moss and liverwort sporophytes die off.

  • Tracheophytes, or "vascular plants", are dominated by the sporophyte generation.

Introduction to the Plantae

Kingdom: Plantae (This link was modified by request of the site's author.At the time this writeup was constructed, found at

DMOZ Open Directory

Classification of Plants, Whittaker FIVE KINGDOM SYSTEM (1978) - Kingdom IV: Plantae

So I've burned a few brain cells on proving the inherent primacy of the order Aves over Primates, and savoring the smell of fried myelin, I move on to bigger things. Images of kings playing cards on fat green stools dancing in my head, I set out to commit a bit of taxonomic regicide and set kingdom against kingdom.

I'm a gardener by trade. It's funny for me to say that because I graduated from college and should be something other than a gardener. Playing in the dirt has given me a heightened appreciation of the silent menace underneath our own hopelessly plantigrade feet. Few things live more like extensions of the earth than do plants. Fungi are pretty awesome, but all they do is feed off decomposing organic matter and only rise to meteoric dominion in the wake of mass extinction events. Protists and bacteria work their usually unseen wonder, and were really big for a while, until the music started slowing down and a few clades decided to drop some Everclear in the evolutionary cooler of hunch punch and wound up covering the whole land area of the planet (and a good chunk of its sea area) in chlorophyll.

Plants are what's up. It's true that they can't really do anything without bacteria and protists at their side, but when they all work together, it's unstoppable. Inch by inch, they cover the ground and set about making the soil their own. Sand gets turned into humus, mixed by generations of fallen brothers and sisters. They give as good as they take --- mineral for mineral, drop for drop.

They're cunning: they expect other kingdoms to mooch off them, so they just shrug and factor it into expenses, all the while, tangling them in a film noiresque web of symbiosis and cooperation. Bees carry pollen. Birds shit seeds. Herbivores wind up being walking fertilizer spreaders. Carnivores serve as an additional measure of selective pressure on herbivores. Animals don't have this earth figured out; it's the kingdom Plantae that's got the whole planet wrapped in its rhizomes and suffer to let the other kingdoms offer it tribute. Linnaeus probably suspected it (and swept that inconvenient little fact underneath the rug), but plants have better shit to do than to come up from out of the snow and contest that claim in the middle of a Swedish winter.

So let it be thus concluded that plants are awesome, and humans are not.

The eminent DonJaime points out that mycorrhizae play an important role in soil remediation as well. I should have made note of this, since I do have a copy of 'Mycelium Running' on my bathroom shelf. Apologies to Fungi, but they're still heterotrophs, and therefore, not as awesome as plants.

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