58 Benedict, JC, ML DeVore, and KB Pigg. 2011

Prunus and Oemleria (Rosaceae) Flowers from the Late Early Eocene Republic Flora of
Northeastern Washington State, U.S.A.
Author(s): John C. Benedict, Melanie L. DeVore, and Kathleen B. Pigg
Reviewed work(s):
Source: International Journal of Plant Sciences, Vol. 172, No. 7 (September 2011), pp. 948-958
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/10.1086/660880 .
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Int. J. Plant Sci. 172(7):948–958. 2011.
Ó 2011 by The University of Chicago. All rights reserved.
1058-5893/2011/17207-0010$15.00 DOI: 10.1086/660880
PRUNUS AND OEMLERIA (ROSACEAE) FLOWERS FROM THE LATE EARLY EOCENE
REPUBLIC FLORA OF NORTHEASTERN WASHINGTON STATE, U.S.A.
John C. Benedict,1 ,* Melanie L. DeVore,y and Kathleen B. Pigg*
*School of Life Sciences, Arizona State University, P.O. Box 874501, Tempe, Arizona 85287, U.S.A.; and yDepartment of Biological and
Environmental Sciences, Georgia College and State University, Campus Box 081, Milledgeville, Georgia 31062, U.S.A.
Two genera of Rosaceae are described from the latest early Eocene Republic flora of northeastern
Washington State, United States. Prunus cathybrownae sp. nov. (Rosaceae: subfamily Spiraeoideae, tribe
Amygdaleae sensu Potter et al.) is based on eight flowers, including one containing in situ pollen and two
immature fruits. Flowers are actinomorphic, perigynous, and pentamerous, with a campanulate hypanthium
bearing five sepals. The gynoecium is unicarpellate and consists of a distally flared, bilobed stigma; an elongate
style; and an ellipsoid, bilaterally asymmetric ovary. Two whorls of stamens—an inner one in which stamens
are reflexed and an outer whorl of extended stamens—are both inserted into the hypanthium. Pollen from the
outer whorl is 20 mm in diameter and tricolporate with a striately ornamented exine; clusters of smaller,
presumably immature grains 7 mm long and 4 mm wide lacking distinctive ornamentation were recovered from
the inner whorl. Immature fruits differ from the flowers in either having a senescent style or lacking one entirely
and having fewer remnants of perianth parts and a larger and more symmetrical ovary. A second flower,
Oemleria janhartfordae sp. nov. (Rosaceae: subfamily Spiraeoideae, tribe Osmaronieae sensu Potter et al.) is
actinomorphic and perigynous and has five free pistils that each resemble the solitary pistil of Prunus. These
include a flattened, bilobed stigma and an ellipsoid, bilaterally asymmetric ovary. The fossil has the laterally fixed,
elongate style characteristic of the genus. These fossils are the oldest known floral examples of these two genera
and demonstrate that both Prunus and Oemleria were present in the latest early Eocene in western North
America. The Okanogan Highlands floristic province provides the earliest fossil evidence to date for the first
major radiation of the Rosaceae, an important mostly temperate, mostly Northern Hemisphere family.
Keywords: Amygdaloideae, fossil flower, hypanthium, Okanogan Highlands, Osmaronieae, Amygdaleae.
Introduction
nectar glands that resemble those characteristic of many extant Prunus leaves (DeVore and Pigg 2007).
Prunus first appears in the fossil record in the early Eocene
in western North America and Europe and also has a distinct
presence in the Holocene, where endocarps and pollen are often found within archeological settings (Anderson and Muller
1975; Pollmann et al. 2005). However, to date no fossil
flowers of this genus have been described. Until recently, the
oldest presumed record of Prunus reproductive structures
was a report of endocarp casts from the Paleocene of western
North America assigned to Prunus corrigus Brown (Brown
1962). Recently, these fossil fruits have been reinterpreted as
members of the Icacinaceae (Pigg et al. 2008). A single endocarp from the lower Eocene of the Wilcox group of the southeastern United States was described as Prunus nabortensis
Berry, and an associated flower type, Antholithes pruniformis
Berry, was interpreted as being related to this fruit (Berry
1916, 1930). Both of these specimens are in need of restudy.
The Eocene of northwestern North America currently provides our oldest reliable record of Prunus fruits. Permineralized endocarps are known from the latest early to earliest
middle Eocene Princeton chert of central British Columbia,
Canada (Cevallos-Ferriz and Stockey 1991) and the slightly
younger Clarno Nut Beds of Oregon (Manchester 1994). Endocarps preserved mostly as casts have been reported from
numerous Tertiary sites in Europe from the Eocene on (Kirch-
The family Rosaceae has a good fossil record that extends
from the early Eocene on in Europe and North America
(Kirchheimer 1973; Mai 1984, 1995; DeVore and Pigg 2007).
Although the record is predominantly of compressed leaves,
fossil fruits, wood, and pollen attributed to the family are
also known. The family is particularly well represented in the
early Eocene Republic flora of northeastern Washington State
and other Okanogan Highlands floras of central British
Columbia (Wehr and Hopkins 1994; Greenwood et al. 2005).
More than a dozen rosaceous genera are represented in these
mostly temperate ‘‘upland’’ floras, including extant genera,
forms similar but not identical to extant genera, and others
that are completely extinct (Wehr and Hopkins 1994; DeVore and Pigg 2007).
Perhaps the most frequently encountered leaf type in the
flora belongs to the genus Prunus L. These leaves show
a range of variability that has yet to be described in detail;
however, four to five different types were informally recognized by J. Wolfe (W. Wehr, Burke Museum of Natural History and Culture, personal communication, 2000). Some bear
1
Author for correspondence; e-mail: [email protected].
Manuscript received December 2010; revised manuscript received May 2011.
948
BENEDICT ET AL.—FOSSIL PRUNUS FLOWERS
heimer 1973; Mai 1984, 1995; Collinson et al. 1993). Rosaceous wood with the characteristic features of Prunus, including traumatic resin ducts, is known from Clarno, the
Princeton chert, and the Eocene of Yellowstone National Park
in Wyoming (Wheeler et al. 1978; Cevallos-Ferriz and Stockey
1990; Wheeler and Manchester 2002). Stratigraphically younger occurrences of fossil rosaceous wood have been reviewed
(Wheeler and Manchester 2002; Wheeler and Dillhoff 2009).
Rosaceous fossil pollen accepted by Muller (1981) has
been described from the Oligocene and lower Miocene of
Cameroon (Salard-Cheboldaeff 1978), the upper Miocene of
northwest Borneo (Anderson and Muller 1975), the Pliocene
of Germany (Menke 1976), and the Pliocene of the Netherlands (Zagwijn 1960). Earlier occurrences are less substantiated, although Taylor (1990) notes an occurrence in the
Eocene of California (Frederiksen 1983), and Zetter et al.
(1999) tentatively assign grains from the Eocene of Argentina
to the family. In the Okanogan Highlands, Rosaceae has been
identified in a preliminary same-grain study of the Princeton
chert (Zetter 2004) as well as in pollen profiles based on light
microscopy (LM) alone (Dillhoff et al. 2005; Greenwood
et al. 2005; Moss et al. 2005).
To date, the only floral remains of Rosaceae known from
the Okanogan Highlands are the permineralized flowers of
Paleorosa similkameenensis Basinger that occur in the Princeton chert (Basinger 1976; Cevallos-Ferriz et al. 1993). Paleorosa is an extinct genus that combines traditional characters
delimiting the two traditional subfamilies Spiraeoideae and
Maloideae. The genus was assigned to Spiraeoideae on the
basis of having a follicle as its fruit type; however, similarities
to Maloideae were noted in floral morphology, seed vasculature, and pollen morphology (Cevallos-Ferriz et al. 1993). Its
strongest similarities to an extant genus were noted to be
with Pyracantha Roemer.
In this report, we describe Prunus cathybrownae Benedict,
DeVore, & Pigg, sp. nov. (Rosaceae: subfamily Spiraeoideae,
tribe Amygdaleae sensu Potter et al. 2007), the first reliable
Prunus flowers and young fruits to be recognized in the Tertiary record. The species is based on eight specimens of laterally compressed flowers, one of which contains in situ pollen,
and two young fruits. Specimens of P. cathybrownae provide
critical floral characters previously unknown from the fossil
record that place these flowers confidently with the genus and
thereby provide a point of reference for its diversification.
A second rosaceous fossil flower from Republic demonstrates the characteristic features of the monotypic Oemleria
cerasiformis (Torr. & A. Gray) Landon known as the osoberry or flowering plum (Stein 2008). Oemleria janhartfordae Benedict, DeVore, & Pigg, sp. nov. (Rosaceae: subfamily
Spiraeoideae, tribe Osmaronieae sensu Potter et al. 2007) is
described from a single distinctive flower with five free carpels that each have characters similar to Prunus, including
a flattened bilobed stigma; elongate laterally fixed style; and
an ellipsoid, bilaterally asymmetric ovary. Today this monospecific genus is endemic to the Pacific Northwest, with a range
from northern California to southwestern British Columbia
(Pojar and MacKinnon 2004; Stein 2008). These fossils provide the first evidence of diagnostic floral characters that
clearly demonstrate that these two genera were present in the
latest early Eocene of western North America. They doc-
949
ument further details of mode and tempo of the diversification
of the Rosaceae, an important mostly temperate, mostly Northern Hemisphere family (Hutchinson 1964; Heywood 1993).
Material and Methods
Fossil flowers are preserved as coalified compressions in
the Republic flora of Republic (Ferry Co.), northeastern
Washington State, United States, where they occur in a light
gray lacustrine shale. All Prunus specimens and the Oemleria
flower were collected from the Boot Hill locality, a site where
both researchers and the public have collected steadily for
more than 20 yr. The fossiliferous horizon occurs within the
Tom Thumb Member of the Klondike Mountain Formation.
Dating by 40Ar-39Ar dating listed in an abstract by Wolfe
et al. (2003) gives an age of 49:42 6 0:54 Ma, which is considered late early Eocene (see Greenwood et al. 2005).
Flower and fruit specimens were photographed with LM.
Fragments of anthers from both the inner and the outer
whorls of the holotype flower R2 (SR 96-11-47AB) were removed. Anther fragments from the inner whorl yielded clumps
containing many very small grains. These were coated with
;20 nm of gold coating, mounted on stubs, and viewed on
a Leica-Cambridge (Structure Probe, Westchester, PA) stereoscan 360FE SEM at 10 kV. Anthers from the outer whorl
contained fewer, larger pollen grains that were treated with
hydrofluoric acid and isolated by heavy liquid separation using zinc chloride. Extant specimens of Prunus flowers were
dissected and photographed with LM. Fossil specimens and
photographs are housed at the Stonerose Interpretive Center,
Republic, Washington, and extant comparative material is
housed in the Paleobotanical Collections, School of Life Sciences, Arizona State University, Tempe.
Systematics of Prunus cathybrownae
Class—Magnoliopsida
Subclass—Rosidae
Order—Rosales
Family—Rosaceae Juss.
Subfamily—Spiraeoideae C. Agardh
Tribe—Amygdaleae Juss.
Genus—Prunus L.
Prunus Type Species—Prunus domestica Linn. B.H. 1:609
Species—Prunus cathybrownae Benedict,
DeVore, & Pigg, sp. nov.
Species diagnosis. Flowers with pedicels 3–8 (up to 15)
mm long (X ¼ 6:15, n ¼ 10) 3 0.5–1.0 mm wide (X ¼ 0:7,
n ¼ 10); actinomorphic, perigynous, pentamerous; hypanthium
campanulate, 3–4 mm long (X ¼ 3:2, n ¼ 7) 3 4–6 mm wide
(X ¼ 4:29, n ¼ 7), length : width ratio 0.75 : 1, hypanthial rim
with inserted sepals and stamens; sepals five, 1 mm long 3 1
mm wide, ovate with pointed apical tip; gynoecium unicarpellate, stigma distally flared, 0.5–1 mm wide, bilobed; style
elongate, 1–4 mm long 3 0.5–1.0 mm wide; ovary 1.5–3.0
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INTERNATIONAL JOURNAL OF PLANT SCIENCES
long (X ¼ 2:6, n ¼ 6) 3 1–2 mm wide (X ¼ 1:83, n ¼ 6), ellipsoid, bilaterally asymmetric; produced in two whorls, inner whorl reflexed, outer whorl extended; anthers dorsifixed;
mature pollen tricolporate, striate, 20 mm in diameter; immature fruits 4.5–5.0 mm long 3 3.0–3.5 mm wide with partially symmetrical ellipsoid ovary.
Previous illustrations. DeVore and Pigg 2007, figures 1–4.
Type locality. Boot Hill (University of Washington Burke
Museum of Natural History and Culture locality B4131), Republic, Ferry County, Washington.
Stratigraphy. Late early Eocene, Tom Thumb Member of the
Klondike Mountain Formation; 49:42 6 0:54 Ma on the basis
of 40Ar-39Ar dating (Wolfe et al. 2003; Greenwood et al. 2005).
Holotype. R2, SR 96-11-47AB (figs. 1A, 3D, 5A, 5C–
5G), collected by a Stonerose staff member, housed at Stonerose Interpretive Center, Republic, Washington.
Paratypes. Specimen and Stonerose collection number,
followed by collector: R1, SR 05-05-06AB, A. H. Smith (figs.
1D, 2C, 2D, 3B, 3C); R7, SR 05-05-03, C. Backman (fig.
1G); R12, SR 96-09-09, D. Gibson (fig. 1I); R40, SR 08-0606AB, J. Shafer (figs. 1C, 2E, 3E); R41, SR 08-40-21AB, D.
Marino and E. Bensing, (fig. 1F); R42, SR 09-09-25AB, M.
Stevens (figs. 1K, 3H); R43, SR 09-09-12AB, C. Middleton
(figs. 1J, 3G); R45, SR 09-09-19AB, J. Armstrong (not figured); and R60, SR 08-42-02AB, M. Jones (figs. 1E, 2A, 2F,
3F, 3I). All paratypes are housed at Stonerose Interpretive
Center, Republic, Washington.
Etymology. The species epithet cathybrownae is named
in honor of three generations who bear this name: Catherine
Louise Brown, Director of Stonerose Interpretive Center, Republic; her mother, Catherine Evelyn Brown, Republic, artist
and enthusiastic supporter of Stonerose; and her daughter,
Catherine Clementine Brown, special assistant at Stonerose.
We honor their extraordinary dedication to the curation and
study of Republic fossils through Stonerose Interpretive Center and its mission of community and educational outreach.
Description
The description is based on 10 laterally compressed specimens, eight of which are part-counterparts, while the remaining two are individuals. Eight of these are mature flowers
with features remarkably similar to those of extant Prunus
(fig. 1A–1I); two are immature fruits (fig. 1J, 1K). Flowers
are actinomorphic, perigynous, and pentamerous and are characterized by a campanulate hypanthium (figs. 1C, 1F, 1G,
2A, 2E). Sepals and stamens are inserted along the apex of
the hypanthial rim (fig. 2A, 2C–2F). The gynoecium is unicarpellate with a distally flared, bilobed stigma; elongate
style; and an ellipsoid, bilaterally asymmetric ovary (fig. 3B).
All specimens are pedicellate, with the pedicel ranging
from 3 to 8 mm long (X ¼ 6:15, n ¼ 10) 3 0.5–1.0 mm wide
(X ¼ 0:7, n ¼ 10), but are incomplete, and their entire
lengths are unknown (fig. 1C, 1E, 1F). One small flower (fig.
1G) has a pedicel 15 mm long 3 1.0 mm wide. The campanulate hypanthium is 3–4 mm high and 4–6 mm across, with
a length : width ratio of 0.75 : 1, and extends around the
base of the gynoecium. In some specimens it is well preserved
(figs. 1A, 1C, 1E–1G, 2A, 2E), while in others only remnants
remain (figs. 1D, 1I, 2C, 2D). Sepals preserved in a few
flowers are 1 mm long 3 1 mm wide and broadly ovate, with
a pointed apical tip (fig. 2A, 2F). Although petals of various
types are known in the Republic matrix, none have been
found in attachment to P. cathybrownae flowers, suggesting
that, as in extant Prunus, they fell off postanthesis.
At the apical end of the gynoecium, the stigma is bilobed
and up to 1.0 mm wide (fig. 3C–3E). It extends into an elongate style (figs. 1A, 1D–1G, 2D, 3B) that is typically 1–4
mm long (X ¼ 2:6, n ¼ 7) 3 0.2–1.0 mm wide (X ¼ 0:5,
n ¼ 6), for a length : width ratio of 6.4 : 1. In one specimen,
the style is notably shorter and thicker, measuring 2.0 mm
long 3 0.8 mm wide (fig. 1C). In the flower specimens (figs.
1A, 1C–1E, 1G, 1I, 3B), the ovary is 1.5–3.0 mm long
(X ¼ 2:6, n ¼ 6) 3 1–2 mm wide (X ¼ 1:8, n ¼ 6).
Two specimens are of immature fruits. In contrast to the
flowers, each has a larger and more symmetric ovary and
fewer perianth parts. The ovary is 4.5 mm long 3 3.0 mm
wide in one fruit (figs. 1J, 3F, 4D) and 5.0 mm long 3 3.5 mm
wide in the other (fig. 1K). One shows the remnant of a style
at the apex (figs. 1J, 3F, 4D), while in the other the style is
lacking (figs. 1K, 3G).
The androecium is characterized by around a dozen stamens borne in two whorls. In the outer whorl, stamens have
filaments ;6 mm long extending apically above the gynoecium (figs. 1A, 1D–1F, 2A, 2C, 2D, 5A). In the inner whorl,
stamens are reflexed and extend to the level of the style base.
Some stamens of the inner whorl are arranged loosely to one
another along the hypanthial rim, such that they superficially
appear to be branched (figs. 1D, 2C), as in extant Prunus (figs.
1H, 2B). Anthers are 0.5 mm wide and dorsifixed (fig. 5A, 5C,
5F) and are similar to those of extant Prunus (fig. 5B).
Two types of pollen have been found within the flowers.
Clusters of small grains 7 mm long and 4 mm wide are found
in the anthers of the inner whorl of reflexed stamens (fig. 5D,
5E). These grains have an exine with poorly defined ornamentation (fig. 5E). Mature rosaceous pollen was recovered from
an anther of the outer whorl of stamens. As seen in LM, these
grains are 20 mm in diameter and tricolporate, with a striate
ornamentation with lumina around 1 mm across (fig. 5G–5H).
Systematics of Oemleria janhartfordae
Class—Magnoliopsida
Subclass—Rosidae
Order—Rosales
Family—Rosaceae
Subfamily—Spiraeoideae C. Agardh.
Tribe—Osmaronieae Rydb.
Genus—Oemleria Reichenb.
Type Species—Oemleria cerasiformis (Torr. &
A. Gray ex Hook. & Arn.) Landon
Species—Oemleria janhartfordae Benedict,
DeVore, & Pigg, sp. nov.
Species diagnosis. Flower bractate, pedicellate, pedicel 11
mm long 3 1 mm wide; actinomorphic, perigynous; gynoecium
Fig. 1 Fossil Prunus cathybrownae sp. nov. (A, C–G, I–K) and extant Prunus cerasus (B, H) for comparison. A, Holotype specimen. R2, SR
96-11-47A. B, Extant P. cerasus flower cut in longitudinal section. C, Flower with short, stout style and campanulate hypanthium. R40, SR 08-0606A. D, Flower showing a campanulate hypanthium with attached stamens. R41, SR 08-40-21A. E, Flower with well-preserved gynoecium,
sepals, and filaments. R60, SR 08-42-02A. F, Flower with gynoecium, hypanthium, and attached perianth parts. R1, SR 05-05-06B. G, Small
flower with long pedicel. R12, SR 05-05-03. H, Extant flower for comparison. Hypanthium has been removed from front of specimen. I, Flower
with flared stigma, bent style, and remnants of perianth. R7, SR 96-09-04. J, Immature fruit. Note remnant of style (arrow). R43, SR 09-09-12A.
K, Immature fruit lacking style. R42, SR 09-09-25B. Scale bars ¼ 3 mm.
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INTERNATIONAL JOURNAL OF PLANT SCIENCES
Fig. 2 Fossil Prunus cathybrownae sp. nov. (A, C–F) and extant Prunus cerasus (B) for comparison. A, Flower with sepals and stamens
attached to hypanthium. R60, SR 08-42-02A. B, Extant P. cerasus flower for comparison. C, Flower with remnants of hypanthium at arrows. R1,
SR 05-05-06A. D, Hypanthium and stamen attachment. R1, SR 05-05-06B. E, Flower with well-preserved campanulate hypanthium. R40, SR 0806-06A. F, Detail of A showing sepals. R60, SR 08-42-02A. Scale bars ¼ 2 mm (A–C, E), 1 mm (D, F).
11 mm long 3 6 mm wide; pistils 5, free, each with a flattened,
bilobed stigma, style laterally fixed, elongate, 3 mm long 3 1
mm wide; ovary 5 mm long 3 3 mm wide, ellipsoid, bilaterally
asymmetric; hypanthium surrounding base of the five carpels.
Type locality. Boot Hill (University of Washington Burke
Museum of Natural History and Culture locality B4131), Republic, Ferry County, Washington.
Stratigraphy. Late early Eocene, Tom Thumb Member of
the Klondike Mountain Formation; 49:42 6 0:54 Ma based on
40
Ar-39Ar dating (Wolfe et al. 2003; Greenwood et al. 2005).
Holotype. R47, SR 08-42-15AB (fig. 6A, 6C–6F), collected by Stonerose staff, 2006; housed at Stonerose Interpretive Center, Republic, Washington.
Etymology. The species epithet, janhartfordae, honors
Jan Hartford of Republic, Washington, for her exceptional
dedication to the collecting and study of the Republic flora
and for developing the customized database Stonerose Strata,
an innovative program that is essential to the workings of
Stonerose Interpretive Center.
Description
Oemleria janhartfordae is based on a single part-counterpart
flower specimen (fig. 6A, 6C–6F) and is quite similar to extant
Oemleria (fig. 6B, 6G). The actinomorphic, perigynous flower
is fractured longitudinally, and its gynoecium is 11 mm long 3
6 mm wide. It is borne on a pedicel 11 mm long 3 1 mm wide.
On the pedicel, an abscission scar is evident, which shows that
the flower was subtended by at least one bract (fig. 6A). The
flower has five free pistils that are basally inserted on the pedicel (fig. 6A, 6C, 6D, 6F). Each bilaterally asymmetric ovary is
around 5 mm long 3 3 mm wide, with a flattened bilobed
stigma 1 mm wide and an elongate style 3 mm long 3 0.5 mm
wide that is attached laterally to the ovary (fig. 6E, 6F). The
five pistils are surrounded by an incompletely preserved hypanthium that covers the bottom half of the ovary wall. Androecia
and petals are lacking; the flower is presumably postanthesis.
General Discussion
Identification of Republic Flowers
The fossil flowers described in this report were identified to
modern Prunus and Oemleria on the basis of highly characteristic floral features of these two genera. These fossils have floral structures that are consistent with not only those of the
modern genera but also ones that are used, essentially, to identify the extant forms. In the case of Prunus, these features include the bilobed stigma, elongate style and asymmetric ovary,
and the characteristic hypanthium (cf. fig. 1A, 1B, 1E; fig. 2A,
2B; fig. 3A, 3B). Oemleria is characterized by five free pistils
that each individually resemble a single Prunus pistil (cf. fig.
6A, 6G; fig. 6B, 6C). In contrast, other rosaceous taxa in the
Okanogan Highlands appear to have mosaic features of modern forms (e.g., Spiraea-like leaves) or to be completely extinct
(e.g., Stonebergia; DeVore and Pigg 2007).
In the most commonly recognized traditional classifications,
Prunus and related genera are placed within Prunoideae sensu
BENEDICT ET AL.—FOSSIL PRUNUS FLOWERS
953
Fig. 3 Fossil Prunus cathybrownae sp. nov. (B–I) and extant Prunus cerasus (A) for comparison. A, Extant gynoecium with flattened, bilobed
stigma and elongate style. B, Gynoecium showing typical flattened, bilobed stigma; elongate style; and elliptical, bilaterally asymmetric ovary. R1,
SR 05-05-06B. C, Detail of B showing stigma in lateral view showing bilobed shape. R1, SR 05-05-06B. D, Detail of holotype specimen showing
lateral view of stigma. R2, SR 96-11-47A. E, Detail of fig. 1C showing top view of stigma with bilobed shape. R40, SR 08-06-06B. F, Ovary with
preserved cellular detail. R60, SR 08-42-02A. G, Immature fruit showing remnant of style (arrow) and ovoid symmetric ovary. R43, SR 09-0912A. H, Immature fruit. R42, SR 09-09-25B. I, Detail of F showing surface of ovary wall. R60, SR 08-42-02A. Scale bars ¼ 2 mm (A, B), 1 mm
(C–F), 3 mm (G, H), 0.25 mm (I).
Rehder (¼Amygdaloideae sensu Takhtajan) on the basis of
their fruit type, the drupe (Rehder 1940; Takhtajan 1997).
Within this subfamily, there has been considerable variation in
both number of taxa and taxonomic levels recognized. Up to
around a dozen genera have been created by some authors,
while others acknowledge a large genus, Prunus, along with
several smaller genera, such as Maddenia, Prinsepia, Exochorda,
and Oemleria (Takhtajan 1997; Potter et al. 2007).
Characters uniting the traditional subfamily include white
to pink flowers; a solitary, umbellate, or racemose inflorescence; 10 to many stamens; free carpels; an ovary with two
ovules that develops into a drupe with one or, rarely, two
seeds; and typically a stony endocarp (Rehder 1940). Prunus
and its segregate genera are unipistillate, with the exception
of Oemleria and Exchorda, which have five free pistils. Petals
and sepals are typically present, unique, and five in number,
with the exception of Maddenia, which has 10 tepals (Chin
et al. 2010). Prinsepia can be distinguished from the other
unipistillate genera by its lateral style (Rehder 1940).
Phylogenies based on recent molecular studies differ considerably from traditional classifications throughout the Rosaceae
(Kalkman 1988, 2004; Potter et al. 2007). In many cases, the
traditional taxonomic units have been collapsed into larger
groups. For example, Maddenia, once considered a distinctive
genus on the basis of a uni- or bicarpellate gynoecium and 10
tepals, is now recognized as a member of Prunus and a part of
the Laurocerasus-Padus clade (Lee and Wen 2001; Bortiri
et al. 2006; Wen et al. 2008; for a discussion and taxonomic
revisions, see Chin et al. 2010). Whereas the traditional classification relied heavily on inflorescence type, this character was
not diagnostic of newly recognized clades (e.g., subgenera
Laurocerasus and Padus, as described by Rehder 1940).
Prunus cathybrownae
Prunus cathybrownae conforms to Prunus on the basis of
the following characters: a campanulate hypanthium, a single
free carpel, five sepals, and at least a dozen stamens. Pistils
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Fig. 4 Line diagram showing gynoecia from several different
developmental stages. A, Small flower illustrated in fig. 1G. Redrawn
from R7, SR96-09-04. B, Flower in fig. 1D. Redrawn from R1, SR 0505-06A. C, Flower in fig. 1I. Redrawn from R12. D, Immature fruit in
fig. 1J. Redrawn from R43, SR 09-09-12A. Scale bar ¼ 5 mm.
are strikingly similar to those of extant Prunus in their morphological features, most notably the flattened, bilobed stigma;
elongate style; and ellipsoid, bilaterally asymmetric ovary.
On the basis of this characteristic shape of the ovary, it can
be inferred that, as in extant Prunus, P. cathybrownae presumably produced two ovules, only one of which would develop into a mature seed (Sterling 1953).
All of the eight flower specimens of P. cathybrownae are
interpreted as being at postanthesis on the basis of the lack
of petals; stamens that usually lack intact anthers; and the
slightly swollen, bilaterally asymmetric ovary. In addition to
size differences, variation in morphology suggests that several
stages are present. Whereas most of the specimens have an
upright style (fig. 1A, 1C–1G), in one the style is bent, suggesting the beginning of floral senescence, as seen in extant
Prunus (fig. 1I, 1H). The formation of an abscission scar beneath the ovary as well as the absence of hypanthia in imma-
ture fruits suggests that the hypanthium was deciduous (fig.
1J, 1K). Together the flower and the two individual fruit specimens are consistent in size with the rate of enlargement observed in extant Prunus flowers and young fruits from full
bloom through early fruit initiation (Tukey and Young 1939).
Features of the stamens also present details of several
stages of floral development. One specimen demonstrates an
inner whorl of reflexed stamens and an outer one of upright
stamens, as noted in extant Prunus flowers (Evans and Dickinson 1999). The clusters of smaller pollen grains recovered
from the inner whorl are interpreted as immature grains.
Whether the exine ornamentation is lacking because of poor
preservation or is simply not yet present at this developmental stage is unknown, but a similar situation was found in
anatomically preserved flowers of Wehrwolfea allenbyensis
(Sapindaceae), known from the contemporaneous Princeton
chert (Erwin and Stockey 1990). The mature pollen found in
the outer whorl of anthers in P. cathybrownae is tricolporate
and has striate ornamentation typical of extant Prunus pollen
(fig. 5G, 5H). This pollen falls within a size range of pollen
known from extant Prunus, which can vary from tricolpate
to tricolporate (Hebda and Chinnappa 1990).
A recent study of character evolution within Prunus assessed the distribution of 25 morphological characters (Bortiri
et al. 2006). Seven of these characters that refer to floral
features can be compared with P. cathybrownae. Prunus
cathybrownae is unicarpellate, with a deciduous, campanulate
hypanthium. Sepals are less than half the length of the hypanthium. The calyx lobe margin is entire and lacks evidence of
a well-developed indument. Flowers are small and, on the basis of one specimen with an elongate pedicel, suggest that the
pedicel may have been longer than the fruit. At the least, fruits
are not sessile. A comparison of the features of P. cathybrownae with the Bortiri et al. (2006) study shows that it has a combination of morphological characters representative of extant
species that occupy basal positions in the genus. At the current
time, it is difficult to resolve the position of P. cathybrownae
within extant Prunus because many of the traditional characters used to classify subgenera and species have been found to
be homoplastic (Shaw and Small 2004; Bortiri et al. 2006).
Prunus leaves are also a relatively common component of
the Republic flora (DeVore and Pigg 2007). Many are elliptic
with a thin lamina and serrate margins with small, regular
teeth, and they presumably were deciduous. These features are
considered basal in the genus (Bortiri et al. 2006). The exact
placement of P. cathybrownae within the genus Prunus cannot
be determined; however, this combination of features seen in
the flowers and associated leaves is consistent with the Republic form(s) of Prunus occupying a basal position in the genus.
In addition to the fossil flowers, young fruits, and leaves of
Prunus from Republic, remains of the genus are known from
several other Eocene localities in western North America.
Anatomically preserved endocarps have been described from
the Princeton chert. These fruits are based on only a few
specimens and were informally designated as types 1, 2, and
3 (Cevallos-Ferriz and Stockey 1991). They have the typical
morphology and anatomical structure of Prunus fruits with
variable distributions of sclereids and fibers, and they have
similarities with the endocarps of the subgenera Prunus
Koehne and Euprunus Koehne (Mai 1984; Cevallos-Ferriz
BENEDICT ET AL.—FOSSIL PRUNUS FLOWERS
955
Fig. 5 Fossil Prunus cathybrownae sp. nov. (A, C–H), all from the holotype specimen (fig. 1A; SR 96-11-47A&B), and extant Prunus cerasus
(B) and extant Prunus dulcis (H) for comparison. A, Androecium surrounding pistil. B, Extant flower showing dorsifixed anthers arranged toward
the gynoecium. C, Dorsifixed anther from outer whorl of stamens. D, SEM of mass of immature pollen from anther of inner whorl. E, Detail of
immature pollen grain. F, Stamen from inner whorl with dorsifixed anther recurving toward the gynoecium G, Pollen from anther of external
whorl. H, Extant pollen for comparison. Scale bars ¼ 2 mm (A, B), 1 mm (C, F), 12 mm (D), 3 mm (E), 20 mm (G), 30 mm (H).
and Stockey 1991). Cevallos-Ferriz and Stockey (1991) commented that it was difficult to demonstrate conclusively the
relationships of the fossil endocarps to extant ones because
specimens lacked some informative characters and because of
the limited knowledge of variability among extant forms.
Two species were described from the Clarno Nut Beds of
Oregon (Manchester 1994), one of which, Prunus weinsteinii
Manchester, was compared closely with type A from Princeton. The other species, Prunus olsoni Manchester, is similar
to extant Prunus avicina (Manchester 1994). Prunus endocarps are also well represented in the fruit and seed floras of
Europe from the Eoceneon, with fossils representing at least
five subgenera of Prunus (Kirchheimer 1973; Mai 1984). To
date, we have not identified Prunus endocarps from Republic. Woody twigs from the Princeton chert (Cevallos-Ferriz
and Stockey 1990) and specimens representing the remains
of larger trees at Clarno and Yellowstone (Wheeler et al.
1978; Wheeler and Manchester 2002) show the characteristic
features of Prunus wood, including traumatic resin ducts.
Oemleria janhartfordae
In addition to reporting the first occurrence of Prunus
flowers in the Tertiary, we now also recognize the first reliable evidence of Oemleria floral remains at Republic. To our
knowledge, the only other fossil report of the genus (under
Fig. 6 Oemleria janhartfordae sp. nov. flower (A, C–F) and extant Oemleria cerasiformis for comparison (B, G). A, Overview of flower with
attached pedicel. Inset, detail of pedicel showing bract scar. R47, SR 08-42-15A. B, Extant O. cerasiformis for comparison. C, Detail of A showing
two of the five pistils (arrows). D, Counterpart of A. R47, SR 08-42-15B. E, Detail of bilobed stigma from D. F, Detail of a single pistil from A
showing lateral style. G, Extant O. cerasiformis flower postanthesis showing separate pistils, line of hypanthial dehiscence, and subtending floral
bracts. B and G courtesy of G. D. Carr. Scale bars ¼ 5 mm (A–D, G), 1 mm (inset in A, E, F).
BENEDICT ET AL.—FOSSIL PRUNUS FLOWERS
its invalid generic name, Osmaronia) was described tentatively from a leaf compression in late Oligocene Creede
flora of Colorado as Osmaronia? stewartiae (Landon 1975;
Axelrod 1987; Schorn and Wolfe 1989). Today Oemleria is
a monotypic genus endemic to western North America, with
a range from the Pacific Coast to the Cascades from northern
California to southwestern British Columbia (Stein 2008).
Plants are dioecious and grow in alluvial or moist soil. It has
been reported that this genus is restricted to a maritime climate (Antose and Allen 1990; Stein 2008).
The occurrence of fossil Oemleria in the Republic flora provides evidence for its early presence in the Northwest. The
geographic distribution of extant Oemleria has been intriguing
to botanists interested in endemic genera. For example, Little
(1971–1981), who compiled species distribution maps for the
trees of North America, hypothesized that endemic forms
were either (1) relicts of older genera that once had a wider
range or (2) young genera that lacked a fossil record. Of the
eight genera he recognized from coastal and subtropical zones
of California, five belong to Rosaceae. Oemleria was of particular interest. Little (1983) speculated that Oemleria originated
from Prunus, lacked a fossil record, and therefore must be
‘‘young.’’ With this report, we can now establish the presence
of fossil flowers belonging to Oemleria co-occuring with those
of Prunus in the latest early Eocene.
Biogeographic Occurrences of Supertribe
Kerriodae (Rosaceae)
In the current classification of Rosaceae (Potter et al.
2007), supertribe Kerriodae comprises two tribes, Osmaro-
957
nieae and Kerrieae. Both of these tribes have fossil representatives at Republic, Oemleria and the genus Neviusia,
previously described from One Mile Creek, British Columbia, and now also known from Republic (DeVore et al.
2004). Oemleria is distributed today on the West Coast of
North America, while the other two genera in tribe Osmaronieae, Exochorda and Prinsepia, are Asian. Kerrieae also has
a North American–Asian disjunct distribution today, with
Kerria and Rhodotypus in Asia, Coloeogyne widespread in
the American Southwest, and Neviusia disjunct between eastern and western North America (Shevock et al. 1992; DeVore
et al. 2004). These newly described fossils plus previously
known fossils from Republic and other Okanogan Highlands
sites underscore the significance of this region as a center of
rosaceous diversification in the Eocene.
Acknowledgments
We thank Catherine L. Brown and Karl E. Volkman, Stonerose Interpretive Center, for loaning us the specimens for
study; Nathan D. Wilkens for technical assistance; Wes Wehr
for identifying many of the specimens; Marilyn B. Canteloupe
for providing extant material of Prunus cerasus; Gerald D.
Carr for providing images of Oemleria cerasiformis; and the
School of Life Sciences, Arizona State University, for SEM
facilities. Jane Maienschein and the Center for Biology and
Society, Arizona State University, provided travel funds. We
dedicate this article to the late Maria Tcheropova, who initially recognized the resemblance of these Republic flowers to
those of modern Prunus.
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