The vital articles project on English Wikipedia began in 2004 when an editor transferred a list from Meta-Wiki: List of articles every Wikipedia should have. The first incarnation of the list became what is now level 3. As of 2019, there are 5 levels of vital articles:
Level 1: the 10 most vital articles (2009)
Level 2: the 100 most vital articles (2009)
Level 3: the 1,000 most vital articles (2004)
Level 4: the 10,000 most vital articles (2006)
Level 5: the 50,000 most vital articles (2017)
Each level is inclusive of all previous levels, meaning that the 1,000 Level 3 articles include those listed on Levels 2 and 1.
Level 5
Animals (1,148 designated out of 2,400)
Animal breeds and hybrids (19/112): 17% complete
Mammals (68/319): 21.3% complete
Birds (33/187): 17.6% complete
Reptiles (25/85): 29.4% complete
Amphibians (6/22): 27.3% complete
Fishes (11/134): 8.2% complete
Crustaceans (3/25): 12% complete
Mollusks (2/19): 21.1% complete
Arachnids (3/17): 17.6% complete
Insects (30/70): 42.9% complete
Cnidarians (5/8): 62.5% complete
Echinoderms (3/6): 50% complete
Porifera (1/4): 25% complete
Other arthropods (3/10): 30% complete
Invertebrates + others (10/27): 37% complete
Agnatha (0/4): 0% complete
Plants, fungi, and other organisms (510 out of 1,200)
Plants (415)
Non-flowering plants (1/30): 3.3% complete
Monocots (2/35): 5.7% complete
Non-monocots (1/88): 1.1% complete
Edible fruits (5/95): 5.3% complete
Edible seeds, grains, nuts (1/69): 1.4% complete
Vegetables (6/96): 6.7% complete
Carnivorous plants (0/2): 0% complete
Fungi (4/33): 12.1% complete
Other organisms--Archaea, Bacteria, Eukarya (5/62): 8.1% complete
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Human 
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Plant morphology 
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Epidermis