The paleobiota of the Latah Formation encompasses both floral and faunal elements preserved in temporary lacustrine environments formed between eruptive phases of the Columbia River Basalts in central to east Eastern Washington and central to north Idaho. The Latah Formation is centered around the greater Spokane area, with a western extent outcropping at Grand Coulee and the eastern margins as far southeast as the area of White Bird, Idaho. Dating of the core Spokane sites is based on the host Grande Ronde Basalts which give an age range of . The Clarkia fossil beds lagerstätte site are slightly younger, being interbedded in the Wanapum Basalts Priest Rapids Member with an age constraint of , or Early Barstovian in age.
The intermittent lakes were surrounded by a temperate ecosystem that was mesophytic in nature, and hosting a diverse flora with plants that are still native to the region and others now restricted to other areas of the globe. There is a small element of the flora that consists of fully extinct genera that are unique to the time and region. Based on work from sampling around Mica, Washington a diverse assembly of diatoms and algae lived in the Spokane area lakes though water conditions for growth were not ideal. The known fauna of the formation is smaller than the flora, with most taxa being insect species though one unnamed Sciuridae fossil was described in 2018, and fish belonging to the salmonid, cyprinid, and centrarchid groups are known. Preservation varies from carbonized compressions at most sites to exceptional organic preservations in some parts of the Clarkia area localities where original organic material is preserved down to living coloration and possible ancient DNA fragments. Upper layers of the Clarkia deposits have been recorded with modern fungi actively feeding on the ancient organic material of the fossils as a food source.
Plants The initial taxonomic work on the flora was undertaken by Frank Knowlton with assistance from diatom specialist Albert Mann and bryologist Elizabeth Britton. Their combined work was published as a supplemental chapter to the initial 1926 descriptive work by Joseph Pardee and Kirk Bryan. After Knowlton's death in November 1926, his revision of the Latah flora was taken over by Edward W. Berry who also erroneously included strata of the much older Klondike Mountain Formation around Republic, Washington. This error was noted and corrected in later works by Roland W. Brown. Ralph W. Cheney and Daniel I. Axelrod broke the Latah into four major florules, Grand Coulee and Spokane in Washington plus Coeur d'Alene and White Bird in Idaho, while noting several "miscellaneous" sites as well. Modern works have concentrated more on single taxa and certain florules.
Mosses Family Genus Species Author/year Florule Notes Synonyms ImagesPolytrichaceae†Polytrichites†Polytrichites spokanensisBrittonSpokaneA possible polytrichaceous mossincertae sedis†Hypnites†Hypnites brittoniae(Steere) MillerSpokaneA moss of uncertain affiliation. Archaeomnium brittoniae (1952) "Moss, genus and species (?)" of Knowlton, 1926 Paleohypnum brittoniae (1946)†Hypnites patens(Britton) MillerSpokaneA moss of uncertain affiliationArchaeomnium patens (1926) Palaeohypnum patens (1946)
Lycopods Family Genus Species Author/year Florule Notes ImagesLycopodiaceaeLycopodium†Lycopodium hesperiumKnowltonCoeur d'AleneA possible lycopod clubmoss Treated as a plant of uncertain affinity by Chaney & Axelrod 1959
Ferns Family Genus Species Author/year Florule Notes Synonyms ImagesBlechnaceaeWoodwardia†Woodwardia praeradicansBerrySpokaneA chain fern speciesEquisetaceaeEquisetum†Equisetum alexanderiBrownSpokaneA horsetail speciesDennstaedtiaceaePteridium†Pteridium calabazensis(Dorf) GrahamMisc - Alkali CreekA Pteridium fern speciesDryopteris idahoensis (of Berry, 1934) Pteris idahoensis (1959)OsmundaceaeOsmunda†Osmunda occidentalis(Berry) BrownSpokaneA royal fern speciesNot to be confused with Asplenium occidentale Knowlton (1917)Asplenium occidentale Berry (1929) Pteris sp. Berry (1929) "Fern, fragment" of Knowlton, 1926WoodsiaceaeWoodsia†Woodsia bonseriBerrySpokaneA cliff fern species
Ginkgos Family Genus Species Author/year Florule Notes ImagesGinkgoaceaeGinkgo†Ginkgo adiantoides(Unger) HeerClarkia Grand Coulee SpokaneA ginkgo species
Conifers Family Genus Species Author Florule Notes Synonyms Images CupressaceaeJuniperus†Juniperus sabinoidesAshleeWhite BirdA juniper speciesMetasequoia†Metasequoia occidentalisClarkiaA dawn redwood species.Taxodium†Taxodium dubium(Sternberg) HeerClarkia Coeur d'Alene Grand Coulee Spokane White Bird Misc localsA bald-cypress.Glyptotrobus aments of Berry, 1929 Sequoia langsdorfii of Knowlton, 1926 Sequoia langsdorfii of Berry, 1929 Sequoia langsdorfii of Berry, 1931Tetraclinis†Tetraclinis salicornioides var. praedecurrens(Knowlton) Kvaček & ManchesterClarkia Grand Coulee Misc-Potlatch (Julietta) Spokane White BirdA Tetraclinis species.Callitris potlatchensis (1935) Fokienia praedecurrens (1959) Fokieniopsis praedecurrens (1997). Libocedrus praedecurrens (1926) Tetraclinis potlachensis (1997)Thuja†Thuja dimorpha(Oliver) Chaney & AxelrodSpokane PinaceaeKeteleeria†Keteleeria heterophylloides(Berry) BrownSpokane Misc-Clearwater RiverA Keteleeria species.Potamogeton heterophylloides (1929)Pinus†Pinus harneyanaChaney & Axelrod 1959SpokaneA pine†Pinus wheeleriCockerellSpokane White BirdA pinePinus monticolensis p.p.(not Republic specimens)Tsuga†"Tsuga latahensis"BerryGrand Coulee SpokaneFirst described as a hemlock conescale.Suggested to be a bud scale in 1937.Treated as an incertae sedis plant by Chaney & Axelrod (1959).TaxaceaeCephalotaxus†Cephalotaxus bonseri(Knowlton) Cheney & AxelrodSpokaneA yewTorreya bonseri (1926) Tumion bonseri (1952)
Basal dicots Family Genus Species Author Florule Notes ImagesNymphaeaceaeNymphaeaUnidentified.ClarkiaA Nymphaea species leafNot describable to species
Monocots Family Genus Species Author Florule Notes Synonyms ImagesAraceaeArisaema†Arisaema hesperiaKnowltonCoeur d'AleneAn Arisaema species. Has been suggested as a synonym of Liquidambar pachyphyllumLysichiton†"Lysichiton washingtonense"BerryGrand CouleeFirst described as a skunk cabbage.Later treated as a species of uncertain affinity.SmilacaceaeSmilax†Smilax magna ChaneySpokane White BirdA green briar speciesAristolochia White Birdensis Ashlee (1932) Smilax lamarensis non Knowlton nec Berry (1929)†Smilax praelaurifoliaAshleeMiscA green briar speciesTyphaceaeTypha†Typha lesquereuxiCockerellSpokane Misc - Arrow Junct.A cattail speciesTypha sp. of Knowlton, 1926UnidentifiedUnidentifiedUnidentifiedSpokaneA poaceous like leaf.Knowlton did not consider Latah Formation leaves as name-able.UnidentifiedSpokanePossibly a poalean plantSuggested to be a low-growing "grass"
Magnoliids Family Genus Species Author Florule Notes Synonyms Images Lauraceae Machilus†Machilus americanaBrownSpokaneA Machilus species†Machilus asiminoidesBrownSpokaneA Machilus speciesPersea†Persea lanceolata(Berry) BrownGrand Coulee Misc-Clearwater River Misc-Juliaetta Spokane White BirdAn avocado speciesLaurus similis (non-typic) Umbellularia lanceolata (1929)UmbellulariaUmbellularia saliciformis(Knowlton & Cockerell) LaMotte Grand Coulee SpokaneA pepperwood species.Laurus similis non Knowlton nec Berry, (1929) Leguminosites bonseri Berry, 1929 (1929) Quercus simulata non Knowlton nec Berry, (1929) Umbellularia dayana non Knowlton nec Brown (1937) MagnoliaceaeLiriodendron†Liriodendron hesperiaBerryClarkia Spokane White BirdA tulip tree species Magnolia†Magnolia dayanaCockerellGrand Coulee Misc-Juliaetta Misc-St Maries Spokane White BirdA magnolia speciesHicoria washingtoniana (1931) Laurus grandis of Knowlton, 1926 Laurus grandis of Berry, 1929 Laurus grandis of Berry, 1934 Laurus princeps of Knowlton, 1926†Magnolia latahensis(Berry) BrownSpokaneA magnolia speciesApocynophyllum latahense (1929) Magnolia californica of Berry, 1929
Ceratophyllales Family Genus Species Author Florule Notes ImagesCeratophyllaceaeCeratophyllum†"Ceratophyllum praedemersum"AshleeSpokaneFirst described as a CeratophyllumReidentified as a possible immature platanaceous fruiting axis.
Basal eudicots Family Genus Species Author Florule Notes Synonyms ImagesBerberidaceaeMahonia†Mahonia simplex(Newberry) ArnoldMisc-Elk River Misc-WeiserAn oregon grape species.Ilex latahensis (1932) Odostemon simplex of Berry, 1934PlatanaceaePlatanus†Platanus dissectaLesquereuxClarkia Coeur d'Alene Grand Coulee Misc-Alkali Creek Misc-Linson Valley Misc-St. Maries Spokane White BirdA Platanus subg. Platanus sycamore leaf species.Acer merriami of Berry, 1929 & 1934†Platanus emryiHuegele, Spielbauer, & ManchesterEmerald CreekA Platanus subg. Platanus sycamore fruit species.Platanus sp fruit of Ashlee, 1932TrochodendraceaeTrochodendron†Trochodendron rosayiManchester, Pigg, & DeVoreEmerald CreekA Trochodendron fruit species.?Trochodendraceae†Nordenskioldia†Nordenskioldia interglacialis(Hollick) Manchester, Crane, & DilcherClarkia Grand Coulee Spokane White BirdA stem-group trochodendralean fruit species.Likely fruits of the leaf species Zizyphoides auriculataCarpites interglacialis (1952) Carpites menthoides (1926) "Equisetum underground stems" (1926) Malva? hesperia (1926) Phyllites amplexicaulis (1926)†Zizyphoides†Zizyphoides auriculata(Heer) Manchester, Crane, & DilcherClarkia Grand Coulee Misc-Arrow Junction Misc-Clearwater River Misc-Juliaetta Misc-St Marie Spokane White BirdA stem-group trochodendralean leaf species.Likely fruits of the fruit species Nordenskioldia interglacialisCebatha heteromorpha (1926) Cocculus heteromorpha (1946) Populus heteromorpha (1926) Populus fairii (1926)
Superasterids - basal Family Genus Species Author Florule Notes Synonyms ImagesCornaceaeCornus†Cornus becki BerryGrand CouleeA dogwood species.†Cornus latahenseChaney and AxelrodSpokaneA dogwood species.Cornus ovalis of Brown, 1937 EbenaceaeDiospyros†Diospyros oregoniana(Lesquereux) Chaney & AxelrodGrand Coulee Spokane White BirdA persimmon speciesDiospyros andersonae (1926)†Remberella †Remberella microcalyx(Knowlton) Manchester & Judd, 2024 Clarkia Emerald Creek Spokane Misc-Oviatt CreekA probable ebenaceous flower.Porana microcalyx (1929) Diospyros? microcalyx (1926)EricaceaeArctostaphylos†Arctostaphylos spatulataBerrySpokaneA manzanita speciesDeemed incertae sedis without commentary (1959) Gaultheria†Gaultheria pacificaBrownSpokane-BrickyardA Gaultheria species†Juddicarpon†Juddicarpon benewahensisSmith & ManchesterClarkiaA vaccinioid fruit.Kalmia?†Kalmia (?) elongataAshleeMisc-Elk RiverA Kalmia speciesRhododendron†Rhododendron knowltoniBerrySpokaneA Rhododendron speciesMenziesia knowltoni (1929)Vaccinium†Vaccinium bonseriBerrySpokaneA Vaccinium species One named subspecies/variety V. b. serrulatum†Vaccinium sophoroidesKnowltonCoeur d'Alene First named as a huckleberry leaf speciesSynonymized into Vaccinium americanum (1929) Resurrected as incertae sedis (1959) †Vaccinium sophoroides(Knowlton) BrownCoeur d'Alene Misc-Juliaetta SpokaneA Vaccinium speciesArctostaphylos knowltoni (1929) Cassia sophoroides (1929) Diospyros princetoniana of Berry, 1929 Phyllites sophoroides (1926) Salix perplexa p. p.HydrangeaceaeHydrangea†Hydrangea knowltoni(Berry) Chaney & AxelrodGrand Coulee Spokane White BirdA hydrangea speciesEuonymus knowltoni (1929) Hydrangea bendirei of Knowlton, 1926, Berry, 1929, Brown, 1937 Gordonia hesperia p. p. Ternstroemites idahoensis of Berry, 1929Philadelphus†Philadelphus pardeei(Knowlton) BrownSpokaneA mock-orange speciesPhyllites pardeei (1926) Phyllites peculiaris (1926)LoasaceaeMentzelia†Mentzelia occidentalis(Berry) BrownSpokane Misc-Julietta Misc-Potlatch River White BirdA stickleaf speciesHibiscus? occidentalis (1929)NyssaceaeNyssa†Nyssa hesperiaBerryGrand Coulee Misc-Linson Valley Spokane