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Paleobotany |
Museum of Paleontology, University of California, Berkeley, California 94720-4780 USA
Received for publication February 23, 2005. Accepted for publication November 14, 2005.
ABSTRACT
Pinus baileyi from the Paleogene of Idaho was initially related to the bristlecone pine P. longaeva (subgen. Strobus, sect. Parrya, subsect. Balfourianae) from western North America. Unlike the centromucronate condition in P. longaeva, P. baileyi cones have raised umbos that are excentromucronate, i.e., the mucro positioned in the upper umbo field above the keel. Cone size and scale morphology shows that P. baileyi more closely resembles excentromucronate pines of subsects. Halepenses and Pinus sensu Gernandt et al. (2005
, Taxon 54: 29–42), but is most similar to P. resinosa, P. kesiya, and P. massoniana of subsect. Pinus. Morphologically, P. baileyi resembles the fossil species P. princetonensis and P. arnoldii from the Eocene Princeton Chert, British Columbia, Canada. Pinus baileyi extends the western North American range of ovulate cones resembling subsect. Pinus from the middle Eocene of British Columbia, Canada and Washington, USA to the Oligocene of Idaho, USA. Pinus baileyi, and possibly P. princetonensis and P. arnoldii, indicates the presence of early populations of subsect. Pinus-type pines in the western cordillera of North America, raising the possibility that P. resinosa and P. tropicalis may have evolved from this group.
Key Words: Balfourianae • Haynes Creek • Idaho • ovulate cones • Paleogene • Pinus baileyi • subsection Pinus • Thunder Mountain
The Eocene Thunder Mountain (approximately 45 million years ago, [mya]) and Oligocene Haynes Creek (approximately 31 mya) fossil sites of Idaho, USA represent rare occurrences of well-dated upland coniferous-hardwood vegetation (Axelrod, 1998a
, b; Taggart and Cross, 2000
). Conifers especially are abundant in both assemblages, with the Pinaceae being well represented by Abies, Larix, Tsuga, Picea, and Pinus (Axelrod, 1998a
, b; Taggart and Cross, 2000
). Axelrod (1998a
, b) monographed the two floras assigning isolated ovulate cones, cone scales, winged seeds, seed wings, fascicles, and vegetative axes to several new and pre-existing species. The new species P. baileyi Axelrod was described and named first from Thunder Mountain based on a cone (Axelrod, 1998a
, pl. 11, fig. 14; holotype UCMP 11082) and several winged seeds (Axelrod, 1998a
). The winged seeds and a five-needled fascicle previously assigned to P. crossii from the Eocene Nevada Copper Basin flora (Axelrod, 1966
, pl. 7. figs. 6-9) were also attributed to P. baileyi, as well as various organs in the unpublished Eocene Nevada Bull Run flora (Axelrod, 1998a
). The P. baileyi concept was added to further with the inclusion of several cones from the Haynes Creek flora, and a different holotype was designated (Axelrod, 1998b
, pl. 4, fig. 10; holotype UF 13487). So the present record of P. baileyi includes ovulate cones, winged seeds, and a five-needle fascicle, and the species occurs in two Paleogene floras in Idaho, USA and two in Nevada, USA.
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]) (Axelrod, 1998a
). However, as shown in this study, P. baileyi cones are excentromucronate (mucro in upper umbo field above the keel [Klaus, 1980
]). This character alone characterizes most Eurasian diploxylon pines of subsect. PinusGernandt et al. (2005)
and the two North American members of the group, P. tropicalis Morelet (western Cuba; Isle of Pines) and P. resinosa Aiton (NE USA and Canada), some Central American species of subsect. Cembroides Engelmann (P. cembroides Zuccarini and P. pinceana Gordon), all true Mediterranean pines, and the Central American P. oocarpa Scheide (Guatemala) (Klaus 1980
, 1989
). Among the excentromucronate pines, P. baileyi cones compare most favorably in size and cone scale morphology to Southeast Asian species of subsect. Pinus.
Recognizing P. baileyi as a pine with cone morphology resembling that of subsect. Pinus allows an opportunity not only to review the fossil record of this group, but also to compare P. baileyi to similar fossil cones and discuss the possible evolutionary and phytogeographic relationships of the plants that bore these cones. We also reassess the associated winged seeds and five-needled fascicle attributed to P. baileyi, and organs associated with P. baileyi described as P. resinosoides Axelrod (Axelrod, 1998a
) and P. ponderosoides Axelrod (Axelrod, 1998b
). Because the extant species here allied to P. baileyi produce similar winged seeds and 2–3-needled fascicles as those assigned to P. resinosoides and P. ponderosoides, it is possible that all or some of these organs may have been produced by the P. baileyi pine.
MATERIALS AND METHODS
Pinus baileyi is re-described from four ovulate cones preserved as three-dimensional adpressions; one from the older Thunder Mountain site and three from the Haynes Creek paleoflora. The Thunder Mountain fossils were deposited in the Thunder Mountain caldera of central Idaho, USA approximately 45 mya (Leonard and Marvin, 1984
; Axelrod, 1998a
). The Thunder Mountain assemblage is from two sites; the stratigraphically lower Dewey Mine locality (UCMP PA959) and the upper Road locality (UCMP PA953). The holotype (UCMP 11082, Fig. 1) is from the Road locality, which consists of 3–4 m of flat-lying, finely laminated, lacustrine shales, that stratigraphically overlie the coarser, volcaniclastic debris layers that make up the basal section of the Dewey Mine Beds. The Dewey Mine florule was interpreted as growing at higher elevation on the walls of the caldera, subsequently transported and buried on the caldera floor, then later covered by lacustrine sediments equivalent to the Road locality. The high degree of abrasion shown by the Dewey Mine fossils indicates they did undergo extensive transport prior to burial.
The Haynes Creek assemblage (UF 18088) is from the Mulkey Member of the Salmon City Formation located northeast of Thunder Mountain. The three Haynes Creek cones come from the darker, denser lacustrine shales of the Lower florule (Axelrod, 1998b
). A rhyolitic tuff that overlies the Haynes Creek plant-bearing beds was radioisotopically dated at 30.7 mya or late early Oligocene (Axelrod, 1998b
).
Specimens were dégaged to expose as much of the fossil as possible. A Silastic (Dow Corning, Midland, Michigan, USA) silicone cast was made of P. baileyi (UF 13487) to reconstruct the cone-scale complex. Photographs were taken either with a Polaroid MP-4 Land (Polaroid, Cambridge, Massachusets, USA) camera using Polaroid Type 55 Positive/Negative film and the negatives scanned using a Leafscan 45 (Eastman Kodak, Rochester, New York, USA) high-resolution scanner or with an Olympus (Tokyo, Japan) CAMEDIA C-700 Ultrazoom 2.1 megapixel digital camera attached to a copystand. Brightness and contrast of digital images were manipulated using Adobe (Mountain View, California, USA) Photoshop 6.0.
By convention, conifer cones are described with the cone apex directed toward the top of the plate, and we follow this format here. In this paper we use subsect. Pinus senusGernandt et al. (2005)
. For comparison, Table 1 summarizes the species included in the older subsect. Sylvestres (Little and Critchfield, 1969
) and the newly proposed subsect. Pinus sensu Price et al. (1998)
and Gernandt et al. (2005)
. Thunder Mountain specimens are in the University of California Museum of Paleontology (UCMP) Berkeley, California, USA. All Haynes Creek material is at the University of Florida Museum of Natural History, Gainesville, Florida, USA (UF). The specimens of extant Pinus examined in this study are housed in the University of California Jepson and University Herbaria, Berkeley, California.
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Family
Pinaceae Lindley
Genus
Pinus Linneaus
Subgenus
Pinus Linneaus
Section
Pinus sensu Gernandt, Geada López, Ortiz Garcia & Liston
Species
Pinus baileyi Axelrod emend. Erwin and Schorn. Pinus baileyiiAxelrod, 1998a
, Univ. California Publ. Geol. Sci. v. 142, p. 37, pro parte pl. 11, fig. 14 only. Pinus baileyiiAxelrod, 1998b
, Univ. California Publ. Geol. Sci. v. 143, p. 44, pl. 4, figs. 9, 10.
Picea deweyensis Axelrod, Univ. California Publ. Geol. Sci. v. 143, p. 43, pro parte, pl. 4, fig. 12.
Holotype
UCMP 11082 (Fig. 1).
Referred specimens
UF13505 (Figs. 2, 6); UF 13518 (Fig. 3); UF 13487a, b (Figs. 4, 5, 7, 8).
Emended diagnosis
Ovulate cones 5–6 cm long and 2.5 cm at widest diameter (closed), conical to oblong, apex tapered. Cone-scale complexes helically arranged: cone scales up to 2.0 cm long, apophyses in plane view, 4–11 mm wide and 4–8 mm high, convex, with transverse keel, upper apophyses mostly rhombic, lower ones 5–6-sided, upper side of scales rounded. Umbo dorsal, in plane view rhombic to elliptic, 1.5–4 mm wide, and 1.0–2.5 mm high, prominent, raised above surface of apophysis, those on basal scales protruding up to 1.5 mm, perexcentromucronate, with mucro erect, curved, sharp pointed, up to 0.5 mm long.
Description
One ovulate cone from the Thunder Mountain flora and two from Haynes Creek were attributed to the new species P. baileyi (Axelrod 1998a
, b) (Figs. 1–4, 8). A fourth cone from Haynes Creek, formerly described as Picea deweyensis Axelrod (Fig. 3, UF 13518) (Axelrod, 1998a
, b), is Pinus and also is most similar to P. baileyi. Both monographs included brief descriptions of P. baileyi and a holotype was named from each locality. The Thunder Mountain cone was published first and therefore takes priority as the holotype according to the International Code of Botanical Nomenclature (Greuter et al., 2000
). Although the holotype appears worn, possibly through pre-burial abrasion or weathering, the shape and size of the apophyses and umbos, umbo position, keel, and eccentric position of the mucro are clearly visible (Fig. 1). The three cones from Haynes Creek are preserved as three-dimensional molds, with some specimens showing limonitic remnants of the cast (dark area Fig. 3). Although no internal anatomy is yet known for this species, the well-preserved apophyses show diagnostic morphological features (Figs. 2–8).
Cones of P. baileyi are conical to oblong, 5–6 cm long, and 2.5 cm wide, with a tapered apex (Figs. 1, 4–6). All are closed. Cone scales are estimated to be up to 2.0 cm long. The apophyses are preserved as depressions and therefore, in life, were not flat but convex. They have a transverse keel (Figs. 1, 2, 4, 5, 7, 8), but do not appear to have an additional central vertical keel (i.e., cross-keeled). In plane view, the shape of the apophyses is typically rhombic in the upper half of the cones, but some in the midregion and near the base show a more pyramidal shape with rounding of the upper two sides (Figs. 2, 6). Still others are pentagonal to nearly hexagonal (Fig. 2). Apophyses in the upper half tend to be broader (6–11 mm wide) and shorter (4–5 mm high), while basal apophyses are narrower (4–9 mm wide) but taller (5–8 mm high). Specimen UF 13487 is a three-dimensional mold consisting of part and counterpart (Figs. 4, 6). It shows slight asymmetry with apophyses in the basal half being relatively smaller than those in the upper half (Figs. 4, 6).
The umbos are dorsal, rhombic to elliptic in plane view, and are relatively larger in the upper half of the cone (3–4 mm wide and 1.5–2.0 mm high), and smaller in the basal half (1.0–2.5 mm wide and 1.0–1.5 mm high). They are raised above the surface of the apophyses (Figs. 5, 8), with some basal ones protruding as much as 1.5 mm. The mucro is strongly eccentric (i.e., mucro in the upper umbo field above the keel) (Figs. 1, 2, 5, 8), and in some extreme cases it sits near or on the upper edge of the umbo (Figs. 7, 8). Klaus (1980
, 1989
) described umbos with eccentric mucros as perexcentromucronate. A silicone cast made of UF 13847 shows the mucros are erect, up to 0.5 mm long, sharp-pointed, and above and separate from the keel (Fig. 8).
Revision of the P. baileyi concept
Our revised concept of P. baileyi excludes some organs previously attributed to P. baileyi. These include two winged seeds from Thunder Mountain (UCMP 11083 and 11084) and a short five-needled fascicle and three winged seeds from the Nevada Eocene Copper Basin flora. Neither of the Thunder Mountain winged seeds is Pinus. UCMP 11084 (Axelrod, 1998a
, pl. 11, fig. 12) is Picea with the characteristic indentation of the seed, the wing is widest in the distal half and has a straight cellular pattern, not the typical wavy pattern diagnostic of Pinus (Wolfe and Schorn, 1990
). In the other, UCMP 11083 (Axelrod, 1998a
, pl. 11, fig. 13), the proximal edge of the wing projects forward beyond its point of attachment, and the seed lacks resin vesicles. These features are more typical of Larix (Wolfe and Schorn, 1990
). The Copper Basin winged seeds also have the indentation of the seed and the straight cellular wing pattern typical of Picea (Axelrod, 1966
, pl. 7, figs. 7-9). The Copper Basin five-needled fascicle is a soft pine assignable to P. crossii Knowlton as discussed by Wolfe and Schorn (1990)
. Although we consider the concept of P. baileyi at this time to include only the cones, there are two- and three-needled fascicles, winged seeds, and seed wings associated with P. baileyi at the Thunder Mountain and Haynes Creek localities that eventually may prove to belong to P. baileyi.
Among these, the Thunder Mountain long, two-needled fascicles were described as the new species P. resinosoides (Axelrod, 1998a
). The long, three-needled fascicles in the Haynes Creek flora were referred to as P. ponderosoides (Axelrod, 1998b
). Although these fascicles are incomplete, the needles are at least 7.0 cm long, with a sheath length of 1.0 cm or more. Both fascicle types have a bilaterally symmetrical base and persistent leaf sheath typical of hard pines (Axelrod, 1998a
, pl. 11, figs. 1, 5). Axelrod related the two-needled fascicles of P. resinosoides to extant P. resinosa of eastern North America and P. ponderosoides to the ponderosa pines, P. ponderosa subsp. scopulorum (Engelmann) E. Murray and P. arizonica Englemann of western North America. The recognition that P. baileyi cones also resemble P. resinosa and related Asian species suggests that the P. resinosoides fascicles may have been produced by the plant that bore P. baileyi cones. However, the Asian species compared to P. baileyi in this paper also produce similar, long two- or three-needled fascicles with persistent leaf sheaths, raising the possibility that the P. ponderosoides-type fascicles may have also been produced by P. baileyi rather than by a P. ponderosa-type pine. Wolfe and Schorn (1990)
have referred the type material of P. ponderosoides to P. crossii Knowlton, so at this time the Haynes Creek three-needled fascicles need to be renamed or referred to an existing taxon. Here we treat them as Pinus species indeterminate (subgen. Pinus) until additional specimens are available to reconcile their affinity.
Isolated winged seeds associated with P. baileyi in the Thunder Mountain flora were attributed to three species: P. alvordensis Axelrod, P. resinosoides, and P. balfouroides Axelrod, whereas winged seeds associated with P. baileyi in the Haynes Creek flora were attributed to two species P. alvordensis and P. ponderosoides. However, assigning isolated winged seeds and seed wings to fossil species is especially difficult and can be misleading because of the potential wide range of seed size and wing shape within a single cone (e.g., see Wolfe and Schorn, 1990
, pl. 3, fig. 5). Difficulty further increases when sample size is small, and there is additional evidence for more than one pine in the assemblage. From our study of the winged seeds in the two Idaho floras, we found little difference in seed size and wing shape among the specimens assigned to these four different species. In addition, there are problems of nomenclature and taxonomy associated with P. alvordensis, P. ponderosoides, and P. balfouroides that need to be addressed in order to better understand the affinities of these isolated winged seeds and any relationship they may have to P. baileyi. Although the Dewey Mine cones attributed to P. balfouroides appear to be Pinus, they are too badly abraded to identify to species; at this time, we cannot determine if these cones represent P. baileyi or another species.
DISCUSSION
Pre-Paleogene fossil record of subsect. Pinus
Millar (1998)
reviewed the fossil record of the genus Pinus. The earliest accepted record is P. belgica Alvin, a permineralized ovulate cone 4.5 cm long and 3.0 cm wide from the early Cretaceous of Belgium (Alvin, 1960
; Miller and Malinky, 1986
; Saiki, 1996
). Pinus belgica was compared to subsects. Contortae, Oocarpae, and Sylvestres (= subsect. Pinus, see Table 1) (Alvin, 1960
). All other fossil remains allied to subsect. Pinus, outside of North America, are from the Late Cretaceous of Japan (Stockey and Nishida, 1986
; Saiki, 1996
). In North America, Late Cretaceous remains attributed to subsect. Pinus include pollen (Pierce, 1957
) and three-needled fascicles from Massachusetts (Robison, 1977
) and New York (Hollick and Jeffrey, 1909). Small ovulate cones of P. clementsii Chaney (Chaney, 1954
) from the Cretaceous of Minnesota that were earlier compared to P. resinosa and the inflated cone scales reported by Penny (1947)
are now discounted as Pinus (Miller and Malinky, 1986
; Axelrod, 1986
).
Cretaceous pollen attributed to genus Pinus (e.g., Pierce, 1957
; Langenheim et al., 1960
; Millar, 1998
), and especially to subsection, probably should be treated with some caution because of the lack of associated megafossils and the prevalence of Pityostrobus and other seed cone genera that are morphologically similar to Pinus (e.g., Miller, 1976
; Smith and Stockey, 2001
, 2002
) and co-occur in the same region in similarly aged deposits. These taxa may have produced similarly appearing Pinus-type pollen as well as winged seeds, pollen cones, fascicles of needle-like leaves, and wood.
The Late Cretaceous Pinus cliffwoodensisMiller and Malinky (1986)
from New Jersey appears to be the only undisputed ovulate cone assignable to Pinus from the Mesozoic of North America. Based on internal anatomy, this species was compared to subsections Ponderosae, Australes, and section Pinea sensu Little and Critchfield (1969)
. Pinus cliffwoodensis cones are small (3.0–4.5 cm long, 2.2–2.3 cm wide) and were described as having a "central spine that is 0.5 mm long" (Miller and Malinky, 1986
, p. 267). However, the mucro looks like it may not be centrally located (i.e., centromucronate), but lies in the upper part of the umbo field above the keel (see Miller and Malinky, 1986
, pl. III, fig. 2). If this interpretation is correct, then P. cliffwoodensis is excentromucronate, making it and P. baileyi the only excentromucronate fossil ovulate cones described thus far from North America. Among the species Miller and Malinky (1986)
compared to P. cliffwoodensis, those with excentromucronate umbos occur in section Pinea, but not Ponderosae. However, among the species included in section Pinea by Little and Critchfield (1969)
, P. canariensis C. Smith shows nearly the full range of mucro position (Klaus, 1989
), but this species differs from P. cliffwoodensis in having large, elongate cones 10–25 cm long, that produce seeds 1.5 cm long, with a wing >4 cm long (Farjon, 1984
). Pinus pinea L., unlike P. cliffwoodensis, also has large cones that are globose (10–12 cm) and seeds 1.0–1.5 cm long. Although cones of subsect. Australes are predominantly centromucronate, P. caribaea Morelet occasionally is duplomucronate with one mucro positioned above the keel, but the cones have an additional centralized spine-like attenuation of the keel (Klaus, 1989
).
Three-needled fascicles of P. triphylla Hollick and Jeffrey from the Late Cretaceous of Massachusetts and New York also appear to be Pinus and were compared to P. tropicalis (subsect. Pinus), P. roxburghii Sargent (subsect. PinasterGernandt et al., 2005
), P. sabiniana Douglas ex D. Don (Ponderosae), and P. occidentalis Swartz (Australes) (Robison, 1977
). These fascicles occur in similarly aged deposits and are geographically close to P. cliffwoodensis, raising the possibility that they may belong to the same group of pines. However, Gaeda López et al. (2002) have questioned the recognition of Late Cretaceous fossils allied to Ponderosae and some other hard pine subsections because these records are inconsistent with their molecular clock estimates.
Comparison of P. baileyi to fossil cones
For the known Tertiary record, megafossils of subsect. Pinus in North America are older than those in Eurasia (Millar, 1998
). Millar (1998)
lists the ovulate cones of P. spinosa Herbst from the Late Eocene of Siberia as being similar to subsect. Pinus and Ponderosae; however, Dorofeev (1963)
compared the cones to P. taeda L. (Australes). Nevertheless, this occurrence is younger than subsect. Pinus-type megafossils found in the early to middle Eocene of British Columbia (Miller, 1973
; Stockey, 1983
, 1984
) and Washington (Miller, 1974
). Hard pine ovulate cones have been reported from the Eocene of Republic, Washington (Wehr and Schorn, 1992
; Schorn and Wehr, 1996
) and the Canadian High Arctic (McIver and Basinger, 1999
), but their subsection affinities have not been determined.
The comparisons between P. baileyi, P. cliffwoodensis, and the Paleogene ovulate cones assigned to section Pinus currently known from North America are summarized in Table 2. Among the three species allied to subsect. Pinus, P. baileyi compares most favorably to the two ovulate cone types from the Princeton Chert, P. arnoldii Miller and P. princetonensis Stockey. Pinus baileyi falls well within the range of both species in cone length and width, scale length, height and width of the apophysis, and umbo position, differing primarily in being excentromucronate. Pinus arnoldii is known from at least 121 permineralized specimens, but no mucro has been observed (Stockey, 1984
). Because the Princeton Chert material rarely fractures along the outside surface of a plant organ, it is often not possible to directly compare the external morphology to compression material. However, as in P. cliffwoodensis, if a mucro were present it could be seen in section view, but only if the section is cut along the plane of the mucro. Pinus princetonensis was also described as lacking a mucro, but this species is similar to P. baileyi in having some umbos that protrude (Stockey, 1984
). Although it is not possible at this time to say whether or not P. baileyi is anatomically more similar to P. arnoldii or P. princetonensis or different, we do propose that P. baileyi and the two Princeton pines may be representative of early ancestral populations of subsect. Pinus-type pines in the upland forests of the western cordillera of North America during the Paleogene.
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; Stockey, 1984
; Phipps et al., 1995
). However, this link is based only on association with no organic connection, and as pointed out by Stockey (1984)
, alternative connections can be made between the Princeton chert cones and leaves, which should not be dismissed until definitive attachments are found (see Stockey, 1984
, p. 273). This concept of a P. arnoldii/P. similkameenensis pine, in part, has been used to infer that the subgenera Pinus and Strobus had not yet diverged by the middle Eocene (Miller, 1973
, 1976
; Stockey, 1984
; Phipps et al., 1995
). Molecular studies, however, have suggested subsect. Pinus had diverged by at least the Paleocene if not earlier (Krupkin et al., 1996
; Geada López et al., 2002
).
Comparison of P. baileyi to extant pines
Unlike P. longaeva, which has the mucro centrally located on the keel (centromucronate) (Figs. 9, 10), the mucro of P. baileyi lies above the keel (excentromucronate). Klaus (1980
, 1989
) recognized among extant pines four types of excentromucronate umbos: duplomucronate, denticulatomucronate, erectoexcentromucronate, and perexcentromucronate. Pinus baileyi umbos are most similar to those described as perexcentromucronate. Perexcentromucronate hard pines include the Mediterranean pines, P. brutia Tenore, P. halepensis Mill., P. pinea, the eastern North American P. resinosa, and the southeast Asian P. kesiya Royle ex Gordon and P. massoniana Lambert (Klaus, 1980
). Cones of P. brutia differ from P. baileyi in being somewhat longer and wider (6–10 cm long, 5–7 cm wide), their apex is often curved, and the apophyses and umbos are flat and may even be depressed (Farjon, 1984
; Klaus, 1989
) rather than protruding. The umbos of P. brutia have also been characterized as having a vallum, a ring-like area encircling the umbo that is differentiated and distinct from it (Klaus, 1980
, 1989
). This feature has not been seen in P. baileyi, but one likely to be preserved and recognized if it were present. Pinus brutia is considered closely related to P. halepensis (Wang et al., 1999
) and some consider it a variety of P. halepensis (Farjon, 1984
). Pinus halepensis cones are similar to P. brutia in being 6–12 cm long and 4–7 cm wide, the apophyses and umbos are typically flat, rectangular to polygonal, and may be vallate (Klaus, 1980
, 1989
). However, in Spain the umbos of some P. halepensis do protrude with well-developed eccentric mucros (Klaus, 1989
). Pinus pinea is a "nut" pine. Unlike cones of P. baileyi, P. pinea cones are large, heavy, and globose up to 10 cm long and 12 cm wide. The apophyses have five radial ribs extending out from the umbo, and the umbo is often surrounded by a vallum (Klaus, 1989
). The seeds are large, 1.0–1.5 cm long, with a short persistent wing (Farjon, 1984
).
Although cones of P. resinosa are also similar to P. baileyi, the mucro of this species is much reduced to absent (Farjon, 1984
; D. Erwin, personal observation). Pinus baileyi more closely resembles extant Southeast Asian members of subsect. Pinus such as P. kesiya (Figs. 11, 12) and P. massoniana (Fig. 13). Pinus kesiya is a three-needled form, but occasionally produces needles in 2s (Farjon, 1984
) and the mucro appears to be mostly reflexed (D. Erwin, personal observation). In P. massoniana (Liguo et al., 1999
) the mucro is erect as in P. baileyi. Today, P. massoniana has an extraordinarily wide range of environmental tolerance. This pine grows from a few hundred to 2000 m in moist river valleys to the dry mountain plateaus of China's interior (Critchfield and Little 1966
, Farjon 1984
). It is also found on Taiwan and Hainan Islands (Farjon, 1984
).
Evolutionary and phytogeographical significance of subsect. Pinus in the Paleogene of North America
Despite more information from the fossil record and molecular phylogenies, the time of appearance and place of origin for the genus Pinus is still speculative as is the divergence of the subgenera Pinus and Strobus (Miller 1976
; Farjon, 1984
; Millar, 1998
; Price et al., 1998
; Gernandt et al., 2005
). From a paleobotanical perspective, Miller (1973
, 1976
) and others have concluded based on fossil species that combine characters of several subsections (e.g., Stockey, 1983
, 1984
; Phipps et al., 1995
), that the two subgenera had not diverged by the middle Eocene (~50 Ma), yet molecular clock estimates suggest several subsections had already diverged 15–20 million years earlier (Krupkin et al., 1996
; Geada López et al., 2002
). These molecular studies unfortunately often imply that fossils that place in subsections that are not synchronous with molecular timelines must be misidentified (Geada López et al., 2002
). Although molecular sequence studies are useful in recognizing monophyly of subgenera, sections, and subsections (e.g., Krupkin et al., 1996
; Price et al., 1998
) and allow for better distinction between common ancestry and parallel or convergent evolution, a distinction that is critical in addressing phylogeny and phytogeographical problems (Liston, 1997
), using molecular clocks to establish the time of appearance may be misleading.
Molecular analyses have yet to resolve the relationship of species within subsect. Pinus, and especially the two North American species, P. resinosa and P. tropicalis (Krupkin et al., 1996
; Liston et al., 1999
; Wang et al., 1999
; Geada López et al., 2002
; Gernandt et al., 2005
). Geada López et al. (2002)
in their analysis using plastid rbcL, matK, the trnV intron, and the rpl20-rps18 spacer, found strong support for P. tropicalis as a member of subsect. Pinus, but found no close relationship to P. resinosa. In the analysis by Gernandt et al. (2005)
using rbcL and matK, they found a sister relationship between the two species P. merkusii and P. massoniana, with P. tropicalis coming out sister to this group, while the relationship of P. resinosa and P. nigra was left unresolved. On morphological grounds, Little and Critchfield (1969)
had considered P. resinosa and P. nigra J.F. Arnold most closely related, as did D. Gernandt and A. Liston (Oregon State University, unpublished data) using molecular data, but Liston questioned the identification of P. resinosa and P. nigra used in this analysis because both GenBank sequences were identical (A. Liston, Oregon State University, personal observation). However, Klaus (1989)
placed P. resinosa in its own subsect. Resinosae close to subsect. Pinus and moved P. tropicalis to Oocarpae. As more and more plant studies incorporate molecular and fossil data to infer phylogenies, calculate molecular clocks, and reconstruct phytogeographic histories, it is important that the researchers report accurate descriptions, identifications, and age dates. Likewise, it is important that GenBank taxa be accurately identified (e.g., the ITS sequence reported for P. krempfii Lecomte was found to be P. armandii Franchet; Liston et al., 2001).
As shown in this study, P. baileyi is excentromucronate and morphologically more similar to Southeast Asian members of subsect. Pinus resembling species such as P. massoniana and P. kesiya. Pinus baileyi adds to our knowledge of fossils resembling subsect. Pinus in western North America, extending the known stratigraphic range of North American subsect. Pinus-type cones from the middle Eocene (approximately 50 mya) to the early Oligocene (approximately 31 mya), and their geographic distribution southeastward to central Idaho. Pinus baileyi, together with the Eocene British Columbia pines P. arnoldii and P. princetonensis, suggest these pines played an important role in the development of upland forests throughout the western cordillera of North America during the Paleogene and at least raise the possibility that P. resinosa and P. tropicalis may have evolved from this group.
FOOTNOTES
The authors thank the reviewers for their constructive comments that greatly improved the paper; A. Liston, Oregon State University, for discussion of extant pine phylogeny; S. Manchester, Florida Museum of Natural History, for loan of the Haynes Creek specimens; B. Ertter, University of California Jepson and University Herbaria for access to extant Pinus material; J. Mason, University of California Museum of Paleontology, for help with specimen preparation; and the Miss Annie Alexander Endowment to UCMP for partial support of this project. This is UCMP contribution no. 1890. 
2Author for correspondence (e-mail: dmerwin{at}berkeley.edu
)
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