Archaeplastida (Land Plants, Algae etc.)1
The various recognised taxonomic groups have changed radically since Carl Linnaeus enumerated them in 1753 (Species Plantarum, first edition). With the creation of seemingly ever more trivial taxonomic ranks and the surgence of cladistics in the late 20th century, higher taxonomy has become both über dynamic and über complex. The situation is increasingly being recognised as artificial, since Linnaeus' taxonomic system is essentially predicated upon false bifurcations. While speciation (the evolution of new species) certainly entails genetic divergence, at the biological level it is far more subtle than incorrigible divisions. Populations often freely hybridise and introgress long after they have "diverged". In reality life is like a long, winding, labrinthyne river. It's salinity level may differ here and there, but such changes are just as natural as the clear continuity of one droplet with the next as they move together through genetic space and time. The odd one being liquidated through evaporation (i.e. extinction).
The conservation status assigned to each entry should be taken as, to varying degrees, tentative. Cases where there is no suitable habitat left are rare, and they may still persist in captivity (knowingly or not). Thus an airtight case for extinction is very difficult to build. While most cases of rediscovery are due to a failure to have previously surveyed significant parts of known or suitable habitat. Or the organism was not, or at least should not, have been feared extinct in the first place. Decades without a record means absolutely nothing in and of itself. While the taxonomic validity or synonymy of a given taxon is somewhat subjective, and there is the very slight risk that a taxon will be (consciously or subconsciously) synonymised in order to reduce the number of extinctions.
Subkingdom: Chlorophyta (Green Algae)
Subkingdom: Embryophyta (Land Plants)
Superdivision: [Anthocerotophyta (Hornworts)]2
Superdivision: Bryophyta (Bryophytes)
Superdivision: Marchantiophyta (Liverworts)
Superdivision: Tracheophyta (Vascular Plants)
(informal): Non-Seed-Bearing Plants
Division: Pteridophyta (Ferns)
Class: [Equisetidae (Horsetails)]
Class: [Marattiidae (Marattioid Ferns)]
Class: [Ophioglossidae (Adder's-Tongues, Grape Ferns, Moonworts, Whisk Ferns)]
Spermatophytes (Seed-Bearing Plants)
Division: Cycadophyta (Cycads)
Division: Ginkgophyta (Ginkgos)
Division: [Gnetophyta (Gnetophytes: Welwitschia etc.)]
Division: Magnoliophyta (Angiosperms or Flowering Plants)
Division: Pinophyta (Conifers)
Subkingdom: Ochrophyta (Brown Algae)
Subkingdom: Rhodophyta (Red Algae)
1 The classification of plants and their allies presented here is a simplified version intended for the general reader. It should not be interpreted as an authoritative taxonomic treatment.
2 Taxonomic ranks encompassed by square brackets (i.e. "[" and "]") have no relevant subordinate taxa. That is, none of the species or subspecies included therein both a) survived at least until the late Pleistocene and b) are considered missing, extinct, rediscovered, or have been removed from these former categories due to taxonomic invalidity. This juxtaposition of non-empty and empty taxonomic units helps to identify potential instances of taxonomic bias in recent extinctions, and by extension those groups of organisms that may have an innate buffer against extinction.