''Pentacentron'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

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 preserve ...

fruits found in the early

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

deposits of northern

Washington state Washington, officially the State of Washington, is a state in the Pacific Northwest region of the United States. It is often referred to as Washington State to distinguish it from the national capital, both named after George Washington ...

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

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), Washington state. The formation is composed of volcanic rocks in the upper unit and volcanic plus lacu ...

Republic A republic, based on the Latin phrase ''res publica'' ('public affair' or 'people's affair'), is a State (polity), state in which Power (social and political), political power rests with the public (people), typically through their Representat ...

. 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 ...

, 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 o ...

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 3 ...

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 are evergreen coniferous trees belonging to the genus ''Abies'' () in the family Pinaceae. There are approximately 48–65 extant species, found on mountains throughout much of North and Central America, Eurasia, and North Africa. The genu ...

spruce A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...

cypress Cypress is a common name for various coniferous trees or shrubs from the ''Cupressus'' genus of the '' Cupressaceae'' family, typically found in temperate climates and subtropical regions of Asia, Europe, and North America. The word ''cypress'' ...

, 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 **Palm oil * Several other plants known as "palm" Palm or Palms may also refer to: Music ...

Taxonomy

The species was described from a

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

, the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

Infructescence In botany, 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 ...

, 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 (biology), isotype ...

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), 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 Geo ...

paleobotanical collections in

Republic, Washington Republic is a city in Ferry County, Washington, United States. The population was 992 at the 2020 census. It is the county seat of Ferry County. It was the largest mining camp in the Republic Mining District, and home to the "Hot Air Line" rail ...

. Manchester ''et al'' published their 2018

type description A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differ ...

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''. 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 (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

''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 (more specifically an avonymic), or an earlier male ancestor. It is the male equivalent of a matronymic. Patronymics are used, ...

honoring Michael E. Sternberg and

matronym A matronymic is a personal name or a parental 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 patrony ...

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'', '' Tetracentron hopkinsii'', and '' Trochodendron nastae''. Additionally the species '' Trochodendron drachukii'' 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 ...

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 i ...

. 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 (: axes) may refer to: Mathematics *A specific line (often a directed line) that plays an important role in some contexts. In particular: ** Coordinate axis of a coordinate system *** ''x''-axis, ''y''-axis, ''z''-axis, common names ...

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, or styles may refer to: Film and television * ''Style'' (2001 film), a Hindi film starring Sharman Joshi, Riya Sen, Sahil Khan and Shilpi Mudgal * ''Style'' (2002 film), a Tamil drama film * ''Style'' (2004 film), a Burmese film * '' ...

, each with an elliptical

nectar Nectar is a viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...

y 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

{{Taxonbar, from=Q7162808 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