''Pentacentron'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

in the family

Trochodendraceae Trochodendraceae is the only family of flowering plants in the order Trochodendrales. It comprises two extant genera, each with a single species along with up to five additional extinct genera and a number of extinct species. The living specie ...

, consisting of the single species ''Pentacentron sternhartae''. The genus is known from

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

fruits found in the early

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

deposits of northern

Washington state Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washington ...

, United States. ''P. sternhartae'' are possibly the fruits belonging to the extinct trochodendraceous leaves ''

Tetracentron hopkinsii ''Tetracentron hopkinsii'' is an extinct species of flowering plant in the family Trochodendraceae. The species is known from fossil leaves found in the early Eocene deposits of northern Washington state, United States and south Central Britis ...

''.

Distribution and paleoenvironment

''Pentacentron sternhartae'' is known from specimens which are recovered from outcrops of the early Eocene,

Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

Klondike Mountain Formation The Klondike Mountain Formation is an Early Eocene (Ypresian) geological formation located in the northeast central area of Washington state. The formation, named for the type location designated in 1962, Klondike Mountain north of Republic, Wash ...

Republic A republic () is a "state in which power rests with the people or their representatives; specifically a state without a monarchy" and also a "government, or system of government, of such a state." Previously, especially in the 17th and 18th c ...

. The Klondike Mountain Formation preserves an upland temperate flora which was first interpreted as being

microthermal In climatology, the term microthermal is used to denote the continental climates of Eurasia and North America. Etymology The word ''microthermal'' is derived from two Greek words meaning "small" and "heat". This is misleading, however, since the t ...

, however further study has shown the flora to be more

mesothermal In climatology, the term mesothermal is used to refer to certain forms of climate found typically in the Earth's temperate zones. It has a moderate span of temperature, with winters not cold enough to sustain snow cover. Summers are warm within oc ...

in nature. The plant community preserved in the Klondike Mountain formation is a mixed conifer–broadleaf forest with large pollen elements of

birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech-oak family Fagaceae. The genus ''Betula'' contains 30 ...

and

golden larch ''Pseudolarix amabilis'' is a species of coniferous tree in the pine family Pinaceae. The species is commonly known as golden larch, but being more closely related to ''Keteleeria'', ''Abies'' and ''Cedrus'', is not a true larch (''Larix''). ' ...

, but also having notable traces of

fir Firs (''Abies'') are a genus of 48–56 species of evergreen coniferous trees in the family (biology), family Pinaceae. They are found on mountains throughout much of North America, North and Central America, Europe, Asia, and North Africa. The ...

spruce A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. ''Picea'' is the sole genus in the subfami ...

cypress Cypress is a common name for various coniferous trees or shrubs of northern temperate regions that belong to the family Cupressaceae. The word ''cypress'' is derived from Old French ''cipres'', which was imported from Latin ''cypressus'', the ...

, and

palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae **List of Arecaceae genera * Several other plants known as "palm" Palm or Palms may also refer to: Music * Palm (ba ...

Taxonomy

The species was described from a

type specimen In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...

, the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

Infructescence Infructescence (fruiting head) is defined as the ensemble of fruits derived from the ovaries of an inflorescence. It usually retains the size and structure of the inflorescence. In some cases, infructescences are similar in appearance to simple fru ...

, number SR 93-08-02, plus a group of eight

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). Of ...

specimens. At the time of description, type series specimens were preserved in the

Stonerose Interpretive Center The Stonerose Interpretive center & Eocene Fossil Site is a 501c(3) non-profit public museum and fossil dig located in Republic, Washington. The center was established in 1989 and houses fossils that have been featured in ''National Geographic M ...

paleobotanical Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeogr ...

collections in

Republic, Washington Republic is a city in Ferry County, Washington, United States. The population was 1,073 at the 2010 census, a 12.5% increase over the 2000 census. It is the county seat of Ferry County. It was the largest mining camp in the Republic Mining Distr ...

. Manchester ''et al'' published their 2018

type description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

of the species in the ''

International Journal of Plant Sciences The ''International Journal of Plant Sciences'' covers botanical research including genetics and genomics, developmental and cell biology, biochemistry and physiology, morphology and structure, systematics, plant-microbe interactions, paleobotany, ...

'' along with the type description of ''

Paraconcavistylon wehrii ''Paraconcavistylon'' is an extinct genus of flowering plant in the family Trochodendraceae comprises a single species, ''Paraconcavistylon wehrii''. The genus is known from fossil fruits and leaves found in the early Eocene deposits of northern ...

''. The genus name ''Pentacentron'' was coined as a reference to the fruits five-fold symmetry, which is distinct from the fourfold symmetry displayed by extant ''Tetracentron'' species. They chose the

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

''sternhartae'' as a combined

patronym A patronymic, or patronym, is a component of a personal name based on the given name of one's father, grandfather (avonymic), or an earlier male ancestor. Patronymics are still in use, including mandatory use, in many countries worldwide, alt ...

honoring Michael E. Sternberg and

matronym A matronymic is a personal name based on the given name of one's mother, grandmother, or any female ancestor. It is the female equivalent of a patronymic. Around the world, matronymic surnames are far less common than patronymic surnames. In som ...

honoring Janet L. Hartford of Republic, Washington. Sternberg and Hartford have helped to facilitate the collecting of fossils at Republic, and promoted the research and education of fossils done through the Stonerose Interpretive center. ''Pe. sternhartae'' is one of between three and four trochodendraceae species that have been described from the Klondike Mountain Formation. Broadly circumscribed, three other species have been identified at Republic, ''Paraconcavistylon wehrii'', ''

'', and ''

Trochodendron nastae ''Trochodendron nastae'' is an extinct species of flowering plant in the family Trochodendraceae known from fossil leaves found in the early Eocene Ypresian stage Klondike Mountain Formation deposits of northern Washington state. ''T. nastae'' i ...

''. Additionally the species ''

Trochodendron drachukii ''Trochodendron drachukii'' is an extinct species of flowering plants in the family Trochodendraceae known from a fossil fruiting structure found in the early Ypresian age Eocene fossils found in British Columbia, Canada. ''T. drachukii'' is one ...

'' is known from related Kamloops group shales at the

McAbee Fossil Beds The McAbee Fossil Beds is a Heritage Site that protects an Eocene Epoch fossil locality east of Cache Creek, British Columbia, Canada, just north of and visible from Provincial Highway 97 / the Trans-Canada Highway ( Highway 1). The McAbee Fos ...

near

Cache Creek, British Columbia Cache Creek is a historic transportation junction and incorporated village northeast of Vancouver in British Columbia, Canada. It is on the Trans-Canada Highway in the province of British Columbia at a junction with Highway 97. The same int ...

. Manchester ''et al'' 2018 noted that ''Tr. drachukii'' is likely the fruits of ''Tr. nastae'', while ''Pe. sternhartae'' are likely the fruits of ''Te. hopkinsii''. If fossils of the fruits and foliage in attachment are found, that would bring the species count down to three whole plant taxa.

Description

''Pentacentron sternhartae'' fruiting spikes range between in length with the fruits arranged long the

axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...

in a helical pattern. Each capsule is

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

on the thin raceme. The capsular heads consist of five fruiting chambers, arranged pentagonally around the midline of the wide head. Growing from the middle area of each chamber is an apically and inwardly curving persistent

style Style is a manner of doing or presenting things and may refer to: * Architectural style, the features that make a building or structure historically identifiable * Design, the process of creating something * Fashion, a prevailing mode of clothing ...

, each with an elliptical

nectary Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists ...

bulge at its base. Rimming the base of each fruit are Perianth scars creating a raised flange. The fruits opened apically, through separation lines running from just above the styles up to the fruit tip where they met to form a pentagonal star like opening.

References

{{reflist, 30em Trochodendrales Plants described in 2018 Ypresian plants of North America Extinct flora of North America Fossil taxa described in 2018 Klondike Mountain Formation Prehistoric angiosperm genera