Picea critchfieldii is an extinct species of spruce tree formerly present on the landscape of North America, where it was once widely distributed throughout the southeastern United States.

[1] The plant was named to honor Critchfield and his longstanding "advocacy of understanding the role of Quaternary history in shaping genetic structure of conifer populations.

"[1] To describe Picea critchfieldii as a new and distinct species, carefully analyzed plant macrofossil specimens of fossilized spruce needles and cones were assessed.

[1] After close examination, these specimens could not be assigned to any extant species of Picea given distinctive morphological and anatomical features of their needles and cones.

[2] Given significant variability among the sporophyte stage for different plant species, macrofossil specimens can exist as seeds, fruits, ovulate cones, needles, leaves, buds, and a host of other forms.

[2] The sporophyte phase of plants is morphologically distinct between different species, which permits species-level identification of macrofossil specimens and thus provides information about past vegetation with "high taxonomic resolution".

[2][1] To glean species-level data, macrofossil specimens must be carefully studied for distinct morphological and anatonomical features that permit their definitive assignment to a particular species, whether extant or extinct.

[1] The specificity and distinctiveness of macrofossil deposits of cones, seeds, and needles were paramount to the identification of the not-previously-known spruce Picea critchfieldii.

[4] Pollen data remains one of the primary mechanisms by which paleoecologists glean insight into past vegetation to catalog the historical presence of taxa on the landscape.

[1] The fossil specimens that aided in the discovery and description of P. critchfieldii mostly originate from stream cut exposures composed of fluvial silt and clay soils from the Late Quaternary.

[1] Eastern North American spruce species that remain extant have boreal and montane affinities and are entirely confined to cool climates.

[7] Sites representative of the Late Quaternary that contain records of flora, fauna, and climates past can be dated with high degrees of accuracy through a variety of methods that allow observational inferences to be made at timescales between 10 and 10,000 years.

[7] As is true for Picea critchfieldii, pollen and macrofossil specimens from a variety of species present during the Late Quaternary have been collected and studied across the globe.

[7] Such specimens are tied to specific locations that can be assigned accurate historical dates, which can then be linked to past climate data that has been independently gleaned from other sources such as ice cores or tree rings.

Given the rich spatial and temporal data embedded in the geologic record of the Late Quaternary, changes in the vegetational composition and structure of the landscape can be studied with great detail.

[1] Within the context of broader climatic changes, hypothesized factors potentially contributing to the decline and extinction of Picea critchfieldii include a pathogen, an inhibited dispersal ability, or a complete loss of suitable habitat.

[7] As Late Quaternary climates changed, plant species responded as individuals in a variety of ways, including toleration, migration, habitat shift, extinction, and altered population densities.

[1] Data from the fossil record also provides evidence that plant species have been able to respond to changing conditions by altering their population densities, transitioning between phases of rarity and abundance while nonetheless persisting on the landscape.