IAWA Bulletin n. s., Vol. 11 (3), 1990: 261-280

VEGETATIVE REMAINS OF THE ROSACEAE FROM THE PRINCETON CHERT (MIDDLE EOCENE) OF BRITISH COLUMBIA

by

Sergio R. S. Cevallos-Ferriz * and Ruth A. Stockey Department of Botany, University of Alberta, Edmonton, Alberta, Canada T6G 2E9

Summary Several anatomieally preserved twigs, a interpretation of a subtropical to temperate branehing speeimen and the wood of a large climate during the time of deposition. axis with affinities to Rosaeeae are deseribed Key words: Rosaeeae, Prunoideae, Maloi­ from the Prineeton ehert (Middle Eoeene) of deae, Prunus, fossil wood, Middle Eo­ British Columbia, Canada. Speeimens are eene. eharaeterised by a heteroeellular pith with a peri-medullary rone of thiek-walled oval eells Introduction and semi-ring-porous seeondary xylem with The Middle Eoeene Princeton ehert local­ vertieal traumatie duets, fibres with eireular ity of British Columbia has a diverse permin­ bordered pits, and mostly seanty paratracheal eralised flora that includes vegetative and and oeeasionally apotracheal parenehyma. reproduetive organs of ferns, conifers, mono­ Ray to vessel pitting is similar to the alternate eotyledons and dieotyledons. Among dicoty­ intervaseular pitting. Seeondary phloem is ledonous plant reproductive organs are flow­ eomposed of tangentially oriented diseontin­ ers represented by Paleorosa similkameenen­ uous bands of alternating fibres and thin­ sis Basinger 1976 (Rosaceae), Princetonia walled eells. Seeondary eortical tissues are allenbyensis Stockey 1987 (incertae sedis), represented by a phelloderm eharaeterised by and a sapindaeeous flower (Erwin & Stockey rectangular eells and phellern with rectangular 1990). Fruits and seeds include Decodon al­ eoneave eells. Anatomical variation between lenbyensis Cevallos-Ferriz & Stockey 1988 speeimens can be related to age of the woody (Lythraeeae), Allenbya collinsonae Cevallos­ axes. Juvenile and mature wood of this spe­ Ferriz & Stockey 1989 (Nymphaeaeeae), and eies differ in vessel arrangement and pres­ Ampelocissus similkameenensis Cevallos­ enee of scanty paratracheal parenchyma in Ferriz & Stockey 1990a (Vitaceae). Addition­ mature wood. Vessel elements are arranged al flowers, fruits and seeds eurrently under in radial multiples, oeeasional clusters as weIl investigation eontinue to demonstrate that a as solitary vessels. Tyloses and dark cellular diverse angiosperm flora oeeurred here dur­ contents are present mainly in mature wood. ing the Middle Eocene. Some twigs have a heterocellular pith with a Although studies of angiosperms at this few scattered cells with dark contents or, loeality have coneentrated on reproduetive occasionally, short irregular rows of these structures, vegetative remains including the cells. In the branching specimen eells of this sterns, roots, and leaves are also weIl pre­ type also are organised in longer rows. To­ served in the chert. Their identification and gether, these anatomical features suggest that attachment to reproductive structures is es­ all specimens belong to the same taxon, Pru­ sential to the reeonstruetion of whole plants nus allenbyensis CevaIlos-Ferriz & Stockey and the understanding of their biology. Vege­ n. sp. Anatomy of this plant reinforces the tative axes from the Princeton ehert are repre-

* Present address: Instituto de Geologfa, Universidad Naeional Aut6noma de Mexieo, Ciudad Universitaria, Apartado Postal 70-296,04510 Mexieo D.F., Mexieo.

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sen ted by a diverse array of twigs, branches Material and Methods and roots. The first angiosperm vegetative Seven rosaceous axes have been found in stern described from Princeton was Eorhiza the Princeton chert (Allenby Formation). The arnoldii, a dicotyledonous rhizome of un­ locality is 8.4 km south of Princeton, British certain affinities (Robison & Person 1973). Columbia on the east side of the Similkameen Recently, Cevallos-Ferriz & Stockey (1990b) River. Fossils occur in a seetion consisting of described Liriodendroxylon allenbyensis, of an interbedded sequence of chert and coal the family Magnoliaceae, based on several with an occasional thin ash bed replacing a twigs and one branching specimen. They chert layer. Forty-nine exposed layers of noted that many of the vegetative axes in the chert have been recorded and systematical­ chert have weil preserved phloem, cortex, ly sampled (Stockey 1987). The locality has epidermis and/or periderm. These authors been referred to as locality 'I' (Boneham stressed the importance of extraxylary tissues 1968) and the 'Princeton chert locality' in the identification of the Princeton fossil (Basinger 1976; Stockey 1984, 1987). The twigs, especially phloem and primary cortical Allenby Formation of the Princeton Group tissues, since some characteristics of juvenile has been dated as Middle Eocene based on wood differ in mature wood (Page 1979). palynology (Rouse & Srivastava 1970), Rosaceous leaf rernains have been reported mammals and fishes (Russell 1935; Gazin from Cretaceous sediments (Hughes 1976), 1953; Wilson 1977, 1982), and potassium­ but it is not until the early Tertiary that flow­ argon dating (Hills & Baadsgaard 1967). ers and fruits are found (Dorofeev 1963; Ba­ Fossils are preserved as silica perminerali­ singer 1976). During the early Tertiary Ro­ sations. All chert blocks were cut into slabs saceae underwent an important adaptative and studied in serial seetions using a modi­ radiation forming a characteristic component fied cellulose acetate pe el technique and of the broad-leaved deciduous vegetation hydrofiuoric acid (Joy et al. 1956; Basinger (Wolfe 1987). Rosaceous remains ofMiddle & RothwellI977). Peel seetions were mount­ Eocene age from the northwestern United ed in Eukitt or Coverbond xylene soluble States and southwestern Canada occur at mounting medium for microseopie exarnina­ severallocalities from Princeton and Joseph tion. Creek, British Columbia, and Republic, In addition to taxa described in the pub­ Washington (Wolfe & Wehr 1988). From lished literature, twigs of extant Crataegus these 10calities about 40 taxa have been iden­ punctata Jacq. (ALTA 10621, UAPC-ALTA tified based on leafremains (Wolfe & Wehr SI 1827), and Prunus pennsylvanica L. (AL­ 1988). Among these leaves are members of TA 72159, UAPC-ALTA SI 1828) were the subfamilies Spiraeoideae, Maloideae, Ro­ compared anatomically to the fossil wood. soideae, and Prunoideae. Rosaceous flowers Wood was dehydrated in 10%, 30%, and from the Princeton chert, Paleorosa similka­ 50% EtOH followed by a tert-butyl alcohol meenensis Basinger (1976), has now been series (Johansen 1940). Paraplast Plus me­ shown to be a member of the subfamily Spi­ dium was used for infiltration and embed­ raeoideae, tribe Sorbarieae (Cevallos-Ferriz ding. Seetions 10-13 ~m thick were cut on a et al. 1990). rotary microtome and stained with safranin­ In the present study a new species, Prunus fast green. allenbyensis Cevallos-Ferriz & Stockey n. sp. The wood identification process was aided (Rosaceae) is described based on vegetative by the computer-assisted identification sys­ stern and wood remains. Anatomical differ­ tem GUESS v. 1.1 and NCSU wood data­ ences in axes of several ages are compared to base (Wheeler et al. 1986; LaPasha & Wheeler similar types of variation seen in extant trees. 1987). All averages represent aseries of 25 This provides the basis for understanding separate measurements (Carlquist 1988). some differences between the anatomy of All specimens are housed in the Uni ver­ young sterns, twigs and more mature wood sity of Alberta Paleobotanical Collection of this fossil plant. (UAPC-ALTA).

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Systematic description thin cuticle. Secondary phloem with alternat­ ing discontinuous bands of tangentially ori­ Class: Magnoliopsida ented fibres and thin-walled cells. Dilated Order: Rosales phloem rays, one to several cells wide, with Farnily: Rosaceae dark contents. Phelloderm up to three cells Subfarnily: Prunoideae thick of rectangular cells. Phellern of concave Genus: Prunus L. cells up to five cells thick. Species: Prunus allenbyensis Cevallos-Ferriz et Stockey n. sp. Description Five twig fragments, averaging 1.0 x 0.7 Etymology - The specific epithet allen­ x 4.0 cm (Fig. 1), a larger branch, 2.3 x 2.0 byensis refers to the abandoned rnining town x 9.3 cm (Fig. 2), and one wood fragment, of Allenby near which the Princeton chert 10- more than 9.4 cm in diameter (Fig. 10; > 16 cality is found. years) have been found in the chert. Anatom­ Holotype - P1095 A (Figs. 14,24,26), ical similarities in primary and secondary tis­ B (Figs. 17, 19,22), P1095 C (Figs. 2,4, sues of all of these vegetative remains enable 9, 11, 13, 15, 16, 23, 25), D (Fig. 8); us to interpret them as belonging to a single Paratypes - Pl184 B (Figs. 1,7); Pl235 taxon. A (Figs. 3, 6, 10,21), D (Figs. 12, 18,20); PlnO C (Fig. 5). Anatomy 0/ the first five growth increments Diagnosis - Pith composed of thin-wall­ Primary tissues - The twigs and the ed polyhedral cells and smaller polyhedral branching specimen are characterised by the thick-walled cells with dark contents either presence of a heterocellular pith and tangen­ organised in rows or scattered at centre, and tially arranged vertical traumatic ducts in the a peri-medullary zone of thick-walled oval secondary xylem. Most pith cells are thin­ cells. Primary xylem containing protoxylem walled and polyhedral or irregular in trans­ elements with helical secondary walls, meta­ verse section (Fig. 3). In longitudinal section xylem tracheary elements with scalariform they are rectangular or irregular, averaging wall thickenings and occasional parenchyma 107 x 73 x 88 11m (Fig. 4). A few polyhe­ cells with dark contents. Secondary xylem dral, thick-walled cells with dark contents semi-ring-porous, with vertical traumatic and smaller dimensions, averaging 46 x 34 x ducts, vessel elements oval to weakly angular 63 11m, are scattered in the pith, sometimes in transverse section, solitary, in radial and forming irregular rows (Figs. 1, 3). The pe­ oblique multiples and occasionally in clus­ riphery of the pith is characterised by four to ters; vessel elements with oblique end walls five layers of larger, thick-walled, oval to and simple perforation plates, alternate inter­ polyhedral cells filled with dark contents, the vascular pitting, and helical thickenings, some peri-medullary region (Fig. 5). In longitudi­ with dark contents and/or tyloses. Fibres nal section these cells are rectangular to quad­ with circular to oval bordered pits (4 11m in rangular, averaging 44 x 22 x nllm. Almost diarn.), and dark deposits in older wood. all pith cells are elongated parallel to the long Uniseriate rays homocellular and heterocel­ axis of the twig (Fig. 4). lular, up to 18 cells high. Multiseriate rays In transverse section axes have about 19 heterocellular with one or two rows of mar­ protoxylem points composed of oval cells ginal cells of upright cells, up to 8-seriate. with a mean diameter of c. 14 11m (Fig. 5); in Vessel to ray pits sirnilar to intervascular pits. longitudinal section these cells have helical Apotracheal diffuse parenchyma, and scanty secondary walls (Fig. 6). Metaxylem cells in paratracheal cells in mature wood. Primary transverse section are also oval with a diam­ phloem fibre bundles present. Cortical cells eter of c. 18 11m (Fig. 5). In longitudinal sec­ oval with dark contents; scattered fibre clus­ tion they can be distinguished from the proto­ ters in cortex, fibres sometimes irregularly xylem elements by the presence of scalari­ shaped. Epidermis ofrectangular cells with a form thickenings (Fig. 6). Associated with

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Figs. 1-4. Prunus allenbyensis n. sp. - Fig. 1. Transverse section of twig showing pith and complete extraxylary tissues. Note prominent banded appearance of secondary phloem, and ver­ tical traumatic ducts in wood. Pl184 B top No. 0, x 10. - Fig. 2. Transverse seetion of larger branch with banded secondary phloem. P1095 C bot No. 0, x 10. - Fig. 3. Transverse section of pith showing irregular rows of cells with dark contents. Pl235 A No. 0, x 150. - Fig. 4. Longitudinal seetion of pith showing chains of cells with dark contents (arrows). P1095 C side No. I, x 125.

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Figs. 5-8. Prunusallenbyensis n. sp. - Fig. 5. Transverse section of large primary xylem bundle. Note thick-walled cells of peri-medullary region. PI720 C bot No. 4, x 110. - Fig. 6. Longitudinal section of primary xylem. Note vessel element of the first growing season. P1235 A side No. I, x 35. - Fig. 7. Oblique transverse section of cortex and radially aligned cells of the periderm. P1l84 B top No. I, x 600. - Fig. 8. Transverse section of secondary phloem with fibre caps of the primary phloem at margin of the cortex (arrows). P1095 D top No: 0, x 250. - C = cortex, MX = metaxylem, P = pith, PE = phelloderm, PL = phellem, PM = peri­ medullary region, PX = protoxylem, VE = vessel element.

Downloaded from Brill.com09/26/2021 11:47:13AM via free access 266 IAWA Bulletin n.s., Vol. 11 (3), 1990 the primary xylem are a few thin-walled pa­ 9). Vessel elements are oval to weakly angu­ renchymatous cells with dark contents. lar with a small diameter (c. 28 11m tang. x 29 The cortex is up to 15 cell layers thick 11m rad.) in wood produced during the first (Figs. 7, 8). Cells in the cortex are thin-wall­ growing season. Vessel diameter increases to ed, oval in transverse section, and average 57 c. 30 11m in the second growth year, and the x 16 x 44 11m, with dark contents. The abun­ wood becomes semi-ring-porous. Vessel ele­ dance of cell contents increases towards the ments continue to increase in diameter in suc­ middle cortex. The cortex is also character­ cessive years. In the last growth ring of the ised by clusters of fibres up to 6 cells in di­ older twig (four years old) vessel element ameter (Fig. 26). At the inner margin of the diameter in earlywood is c. 33 11m (tang.) cortex, primary phloem is represented by x 34 11m (rad.), while in latewood it is c. 26 fibres (Fig. 8). Sieve elements and paren­ 11m (tang.) x 31 11m (rad.). In these first four chyma cells are not preserved. Epidermal growth increments vessel element density is cells usually are not weIl preserved; how­ about 283/mm2• A large proportion of the ever, in some twigs a few crushed cells can wood in twigs is composed of thin-walled be observed covered by cuticle. (sensu Wheeler et al. 1986) fibres, rectangu­ Secondary tissues - In the first five lar to polyhedral in transverse section, aver­ growth rings of the secondary xylem, vessel aging 12 x 18 x 294 11m (Fig. 18). Vertical elements are solitary (c. 5%), in radial and traumatic ducts are present at the beginning oblique multiples of two to four cells (c. 73 of some growing seasons in most twigs %) and occasionally in clusters (c. 21 %; Fig. (Figs. 1, 13). These ducts are either tangen-

Legends to Figures 9-26:

Figs. 9-14. Prunus allenbyensis n. sp. - Fig. 9. Transverse section of secondary xylem of large branch. P1095 C bot No. 0, x 120. - Fig. 10. Transverse section of xylem of the larger piece of wood. P 1235 A No. 2, x 120. - Fig. 11. Radial section showing vessel elements with tyloses. P1095 C side No. 1, x 195. - Fig. 12. Vessel elements with alternate intervascular pit­ ting. P1235 D side No. 4, x 250. - Fig. 13. Transverse section of vertical traumatic canals. P1095 C bot No. 0, x 110. - Fig. 14. Vessel element with simple perforation plates and thin helical thickenings (arrows). P1095 A side No. 1, x 290.

Figs. 15-20. Prunus allenbyensis n. sp. - Fig. 15. Oval, alternate intervascular pitting with coalescent pit apertures (arrow). P1095 C side No. 1, x 1750. - Fig. 16. Circular to oval, alternate intervascular pitting with coalescent pit apertures (arrow). PI095 C side No. 1, x 1500. - Fig. 17. Ray to vessel pits. P1095 B side No. 0 x 900. - Fig. 18. Small vessel element of latewood with helical sculpturing SUITounded by imperforate tracheary elements with distinct1y bordered pits. P1235 D side No. 4, x 130. - Fig. 19. Tangential section of large branch at level close to the pith showing uni- and multiseriate rays. P1095 B side No. 0, x 125. - Fig. 20. Tangential section of larger piece of wood. Note large amount of dark contents. P1235 D side No. 4, x 125.

Figs. 21-26. Prunus allenbyensis n. sp. - Fig. 21. Radial section of uniseriate ray with up­ right cells. P 1235 A side No. 1, x 235. - Fig. 22. Tangential section showing apotracheal parenchyma. P 1095 B side No. 0, x 280. - Fig. 23. Tangential section showing scanty para­ tracheal parenchyma. P1095 C side No.!, x 280. - Fig. 24. Radial section of multiseriate ray with upright and square to procumbent cells. P1095 A side No. 1, x 190.- Fig. 25. Transverse section of secondary phloem. P 1095 C bot No. 0, x 180. - Fig. 26. Oblique radial section of secondary phloem and cortex. P 1095 A side No. 1, x 180. - C = cortex, F = fibres, PH = secondary phloem, R = ray.

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Downloaded from Brill.com09/26/2021 11:47:13AM via free access 270 IAWA Bulletin n.s., Vol. 11 (3), 1990 tially arranged along the whole ring (Fig. 1), Secondary phloem is composed of dis­ or located in only apart of it. Vertical traum­ continuous, tangentially oriented, alternating atic ducts are short (c. 1.5 mm long), and bands of thin-walled cells and fibre clusters distributed in such a way that while an axis (Figs. 1, 2, 8, 25). Thin-walled cells tend to may have them at one level, they may dis­ be ovoid and may represent sieve tube mem­ appear completely at another. Most of the bers. Adjacent to the vascular cambium phlo­ twigs have vertical traumatic ducts in the sec­ em rays are thin (two or three cells wide). ond growth ring. Traumatic ducts lack an They dilate toward the cortex where they may epitheliallining (Fig. 13) and are apparently, be up to 8 cells wide. A few uniseriate rays therefore, lysigenous in origin (Panshin & mayaiso be present. In some twigs rays ap­ De Zeeuw 1980). The brownish contents pear straight in transverse section, but in present in some of these vertical ducts may other specimens they have an undulating out­ represent former cell contents, gum, or per­ line. However, these rays are not always well haps mucilage. preserved and often appear as large spaces Vessel elements have slightly oblique end (Figs. I, 2). Periderm is present in all twigs walls with simple perforation plates (Figs. 6, examined (Fig. 7). The phellern is typically 14, 18), and alternate intervascular pits (c. 6 around five cells thick, but may be more x 4 Ilm) on lateral walls (Figs. 12, 15, 16). extensive in larger twigs. It is composed of Intervascular pitting in some areas is crowd­ rectangular cells with a concave surface fac­ ed, oval, mostly alternate, rarely opposite, ing towards the pith. Three celllayers of rec­ and in very few ca ses scalariform because of tangular cells form the phelloderm in most the coalescence of pit apertures (Figs. 15, 16). twigs (Fig. 7). Vessel elements have thin helical thickenings, especially those of the latewood (Figs. 14, Anatomy 01 the older growth increments 18). These helical thickenings are more com­ The last growth ring of the branching stern mon in smaller vessel elements. Some ves­ and wood of the large wood fragment have sels have dark contents. Fibres have circular anatomy similar to twigs, but differ quantita­ to oval bordered pits, c. 4 Ilm in diameter in tively in several aspects. As in the twigs, the tangential and radial walls (Fig. 18). pith is heterocellular. However, while small Rays are one- to five-seriate and five to 28 cells with dark contents are found both sc at­ cells high (Figs. 19, 20), averaging 370 Ilm tered and in short rows in the central part of (range 150-630 Ilm), and have simple pits the pith in twigs, in the larger branch cells of on radial and tangential walls. There are c. 10 this type are organised into irregular rows rays per riilllimetre. Multiseriate rays are com­ (Fig. 3). The large wood fragment has vessel posed mainly of procumbent cells with one grouping similar to twigs; however, most or two upright cells in the margins (Fig. 24). vessels are solitary (c. 46%), fewer occur in Uniseriate rays 2 to 12 (up to 18) cells high radial and oblique multiples (c. 42%) and near the pith (range 36-115 Ilm). Some rays clusters (c. 12%). Vessel distribution is semi­ are composed of upright cells near the pith ring-porous (Fig. 10); however, there are (Fig. 21), but in later wood they have pro­ fewer (100) and larger vessel elements per cumbent, square, and upright cells. In the square millimetre. Vessel elements almost branching specimen, some multiseriate rays double in size in older wood. In earlywood near the margin of the pith are over 1 mm they have a tangential diameter of 55 Ilm high. In later wood of the same specimen (range 47-65 Ilm) and a radial diameter of 70 rays are c. 500 Ilm high, but as the branch Ilm (range 40-83 Ilm). In latewood vessels grew, rays became shorter. Ray to vessel pits have an average tangential diameter of 32 Ilm are similar or slightly smaller, but less crowd­ (range 28-45 Ilm), and average radial diam­ ed, than intervascular pits (Fig. 17). Paren­ eter of 35 Ilm (range 22-40 Ilm). Tyloses chyma cells with dark contents are also pres­ are frequently found in these larger axes (Fig. ent in the wood and usually form apotracheal 11), while they are rare or absent in the strands up to 7 cells wide and about 5 cells twigs. Vertical traumatic ducts are also pres­ tall (Fig. 22). ent, and as in twigs they apparently have a

Downloaded from Brill.com09/26/2021 11:47:13AM via free access Cevallos-Ferriz & Stockey - Eocene Prunus allenbyensis 271 lysigenous origin. In contrast to smaller axes tata made during this study confirm the con­ in which traumatic ducts are typically empty, stancy of these characters for these two taxa. ducts in the branch and large wood fragment Comparison 0/ wood characters - Four frequently have contents. Multiseriate rays of the characters, i.e. semi-ring-porous are heterocellular, with one or two rows of wood, simple perforation plates, alternate in­ marginal upright cells, up to 8-seriate and are tervascular pitting, and ray to vessel pits sim­ almost 40 cells high (average 360 Ilm). A ilar to intervascular pits that characterise P. few homocellular uniseriate rays up to 12 allenbyensis are found in combination in over cells high are present; however, most unicel­ 50 farnilies of dicotyledonous plants (Wheeler lular rays are heterocellular composed of pro­ et al. 1986; LaPasha & Wheeler 1987). How­ cumbent, square, and upright cells. Paren­ ever, the combination of these and an addi­ chyma cells form apotracheal strands as in tional five characters are found together on­ the twig (Fig. 22), but in a few cases scanty ly in two families, Rosaceae and Meliaceae paratracheal cells not found in twigs are also (Wheeler et al. 1986; LaPasha & Wheeler present (Fig. 23). Vessels and parenchyma 1987). These additional characters include: cells in these more mature woods have more vessel elements with helical thickenings, fi­ dark contents than in the twigs. bres with distincdy bordered pits, gum in vessels, rays commonly 4-1O-seriate, and Discussion vertical traumatic ducts. The most definitive of these characters is the presence of vertical Comparison with extant Rosaceae - Ana­ traurnatic ducts. tomical similarities between all of the vegeta­ Although Prunus allenbyensis has many tive axes under study support their interpre­ characters in common with Meliaceae, the tation as specimens belonging to the same two differ with respect to features of the fi­ taxon. These include: heterocellular pith with bres, distribution of parenchyma, and histol­ a peri-medullary zone, semi-ring-porosity, ogy of the ground tissue. Fibres with dis­ alternate intervascular pitting, simple perfora­ tincdy bordered pits, the high number of ves­ tion plates, fibres with circular bordered pits sels per square millimetre and scanty paratra­ in tangential and radial walls, and ray to ves­ cheal and occasional apotracheal parenchyma seI pits that are similar to intervascular pits. are more reminiscent of Rosaceae than of the The observed variation in vessel element den­ Meliaceae (Wheeler 1989, pers. comm.). AI­ sity, height of rays, amount of dark cellular though pith with a peri-medullary zone has contents and presence of scanty paratracheal been reported in Meliaceae and Rosaceae parenchyma, and tyloses, is consistent with (Metcalfe & Chalk 1950) members ofMelia­ wh at one would expect in wood of different ceae also commonly have either secretory parts of the same tree or different individuals cells (Entandrophragma DC. and Melia L.), of the same species (Schweingruber 1978). or stone cells (Cabralea Juss., Chisocheton General vessel distribution (which may vary Blume, Hearnia Muell., Megaphyllaea Hemsl. slightly in the first few growing seasons), and Sandoricum Cav.; Metcalfe & Chalk type of perforation plate, and type of ray to 1950). Neither are present in the pith of Pru­ vessel pitting are characters that typicallY re­ nus allenbyensis. Secretory cells also charac­ main constant in the above-ground parts of terise the cortex and secondary phloem of selected taxa in Betulaceae, Fagaceae, Platan­ Meliaceae (Roth 1971, 1981) while these aceae and Salicaceae (Schweingruber 1978), cells are absent in P. allenbyensis. while ray structure, for example, can vary The fossil vegetative axes exhibit a large depending on cambial age (Barghoorn 1940, number of characters that typify wood of 1941a, 1941b). Our previous study of twigs Rosaceae. These include: small (but in some of Magnolia L. and Liriodendron L. further genera large) and numerous vessels, a ten­ supports the constancy of Schweingruber's dency to ring-porosity, vessel elements often anatomical characters (Cevallos-Ferriz & with helical thickenings, perforation plates Stockey, 1990b). Observations of extant that are typically simple (but occasionally Prunus pennsylvanica and Crataegus punc- with scalariform or irregular perforation

Downloaded from Brill.com09/26/2021 11:47:13AM via free access 272 IAWA Bulletin n.s., Vol. 11 (3), 1990 plates), mainly alternate or occasionally op­ raeoideae; Metcalfe & Chalk 1950). How­ posite intervascular pitting; axial parenchyma ever, some extant Prunus species and other that is apotracheal diffuse, diffuse in aggre­ taxa in Maloideae have pits with clearly dis­ gates, or sometimes scanty paratracheal; het­ tinct borders (Zhang Shuyin 1989, personal erocellular to homocellular rays that are two­ comm.), as in P. allenbyensis. to five-seriate, or sometimes wider, occa­ In Rosaceae, ray to vessel pits have been sionally with two distinct widths; ray to ves­ described as similar to intervascular pits (Tip­ sel pits often similar to intervascular pits, and po 1938; Fabbri-Tarchi 1960). In Prunus, fibres with distinct bordered pits on radial however, vessel to ray pits are usually much and tangential walls in most genera (Metcalfe smaller than the intervessel pits (Zhang Shu­ & Chalk 1950; Fabbri-Tarchi 1960). yin 1989, pers comm.). Yet in some Prunus Prunus allenbyensis has some characters species (e. g., Prunus serotina Ehrh., Wheeler that can be found in the subfamilies Prunoi­ 1990, pers. comm.) the vessel to ray pits are deae and/or Maloideae. These include pres­ similar in size to the intervascular pits, as in ence of vertical traumatic ducts, vessel distri­ P. allenbyensis. bution, distribution and distinctiveness of Most rosaceous taxa have unicellular rays bordered pits in fibres, type of ray to vessel composed of upright and square cells (Met­ pitting, and type of uniseriate ray. Vertical calfe & Chalk 1950). Rays in Maloideae are traumatic ducts within Rosaceae were thought characterised by their tendency to be homo­ to be almost unique to the subfamily Prunoi­ cellular (Fabbri-Tarchi 1960), while uniseri­ deae (Record 1925; Metcalfe & Chalk 1950). ate rays in extant Prunoideae are heterocel­ Recently these ducts have been reported in lular composed of square and upright cells species of Rosaceae other than those included (Metcalfe & Chalk 1950; Zhang Shuyin 1989, in Prunoideae (Fahn et al. 1986). The combi­ pers. comm.). Through ontogeny ray struc­ nation, however, of vertical traumatic ducts ture is highly variable. Near the pits the fossil and vessel elements in radial and oblique twigs and branch have some uniseriate homo­ multiples, occasional clusters and solitary cellular rays composed of upright cells. How­ vessels, as in P. allenbyensis is more com­ ever, further away from the pith, uniseriate mon in the subfamily Prunoideae. Neverthe­ rays become slightly heterocellular, compos­ less, the higher number of solitary vessels in ed of procumbent, square,and upright cells. more mature wood is reminiscent of Maloi­ Structure of uniseriate rays in fossil Prunus deae (Metcalfe & Chalk 1950; Zhang Shuyin varies from those composed of exclusively 1989, pers. comm.) upright cells (P. palaeozippeliana Suzuki, P. Presence of distinct bordered pits in tangen­ polyporulosa Suzuki) to those with upright tial and radial walls of fibres of the Princeton and square cells (P. ascendentiporulosa Su­ wood is a character shared with most Rosa­ zuki) or with procumbent and upright cells ceae. Metcalfe and Chalk (1950) noted that in [Po iwatense (Watari) Takahashi & Suzuki], most Maloideae and some species of Spiraea to those with at least some rays composed of L. (Spiraeoideae) pits are less common in upright, square, and procumbent cells (P. tangential than in radial walls of the fibres. gummosa Wheeler et al.). This same character is thought to be of im­ We have assigned the Princeton vegetative portance in identifying Prunoideae (Metcalfe axes to Prunus based on the combined pres­ & Chalk 1950; Zhang Shuyin 1989, pers. ence of vertical traumatic ducts and vessels comm.). Preservation of Prunus allenbyensis that occur in oblique and radial multiples, oc­ does not allow a comparison of the abun­ casionally in clusters, as weIl as solitary. dance of pits in tangential and radial walls of the fibres. Difficulty in observing the pit bor­ Comparison 0/ secondary phloem and pith ders in most Prunus species was noted by characters - Of the several patterns that Metcalfe and Chalk (1950). Fibres with pit characterise secondary phloem of rosaceous borders that are difficult to observe are not species, Prunus allenbyensis is most similar restricted to Prunoideae, but can be found to that reported for extant Rubus L. (Rosoi­ for example in some species of Spiraea (Spi- deae; Zahur 1959; Roth 1973). In both taxa,

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the mechanical tissue is weH developed and is Comparison with fossil Rosaceae - At represented by discontinuous tangential bands least 18 rosaceous woods are known from of fibres. Although other species of extant the fossil record (Table 1). They have been Rosaceae also have mechanical tissue, the included in Maloideae (Grambast-Fessard arrangement of the bands seen in the fossil 1966; Wheeler & Matten 1977; Hofmann has not been reported. For example, mechan­ 1944, 1952; Van der Burgh 1974, 1978), ical tissue in the Maloideae species investi­ Rosoideae (Shilkina 1958), Spiraeoideae gated by Zahur (1959) is composed of tan­ (Page 1964), and Prunoideae (Van der Burgh gentially arranged, continuous bands of scle­ 1974; Dup€ron 1976; Wheeleret al. 1978; reids. In Spiraeoideae, Exochorda grandi­ Süss & Müller-Stoll 1980, 1982; Suzuki flora Lindl. is the only species in which phlo­ 1984; Takahashi & Suzuki 1988). In the fam­ em has been studied in some detail, and lacks ily Chrysobalanaceae one species has been sclereids. The most complete description of described (Pfeiffer & Van Heuren 1928). rosaceous phloem is that of Prunus. Phloem Prunus allenbyensis differs from other of the fossil vegetative axes shares the fol­ fossilised rosaceous stern woods, excluding lowing features with extant Prunus: large Prunoideae, by the presence of vertical trau­ number of fibres, and moderate dilation of matic ducts (Table 1). Species of Pomoxylon rays. The presence of U-shaped cells in the (Hofmann 1944, 1952; Van der Burgh 1978) phellern, and lack of a secretory system are differ further from P. allenbyensis in having also shared characters with Rosaceae (Bastin only solitary vessel elements, rather than ra­ 1895; Schneider 1945; Roth 1973). In the dial multiples and clusters ofvessels (Table 1). Chrysobalanaceae, a family thought by some Crataegus and Sorbus L. from the Pleisto­ to be closely related (e.g., Prance 1972, cene of Tegelen, the Netherlands, have ho­ Hutchinson 1973; Cronquist 1988), an ar­ mocellular rays, and mainly solitary vessels rangement sirnilar to that found in the Prince­ (Van der Burgh 1974), in contrast to the het­ ton material has been noted in two species of erocellular rays, and vessels that are solitary, Ucania Aubl. (Roth 1973, 1981). Since the in radial and oblique multiples and clusters phloem of about only 13 out of about 3000 of P. allenbyensis (Table 1). Maloidoxylon species of Rosaceae and only 7 out of 430 coloradoense and M. galbreathii from Co­ species of Prunus has been described to date lorado, U.S.A., and M. castellanense from and the anatomy of this tissue seems to be CasteHane, France, differ in lacking helical quite variable within the family, it would not thickenings, and gum or gum-like deposits be surprising to find phloem with organisa­ (Table 1; Grambast-Fessard 1966; Wheeler & tion like P. allenbyensis in Prunus or taxa of Matten 1977). Rosaceoxylon Shilkina from other subfamilies. Russia is distinct in having septate fibres and Pith like that of Prunus allenbyensis with scalariform intervascular pitting (Table 1; a differentiated peri-medullary region has Shilkina 1958; Süss & Müller-Stoll 1982). been reported in P. padus L., P. avium L., Parinarioxylon is characterised by the pres­ and P. spinosa Walt. (Schweingruber 1978) ence of uniseriate rays and lacks helical thick­ as weH as in other rosaceous genera such as enings (Pfeiffer & Van Heuren 1928). Neillia Don (Spiraeoideae), and Rubus and The root wood described as Pruninium Kerria DC. (Rosoideae; Metcalfe and Chalk kraeuselii (Schönfeld) Süss & Müller-Stoll 1950). As in P. allenbyensis, the presence of (1982) is difficult to compare to Prunus al­ scattered smaller cells with dark contents in lenbyensis since variation in roots is even the pith is a frequent character of Prunus greater than variation in the above-ground (Schweingruber 1978) and other rosaceous axes. However, the root wood of this taxon taxa (Metcalfe & Chalk 1950). The presence lacks vertical traumatic ducts and has rays of small rows of cells between larger cells is with more marginal cells (Süss & Müller• an arrangement found in some twigs and in Stoll 1982). the branching specimen of P. allenbyensis Stern woods described as Prunoideae are and has been noted in Rosa L. (Rosoideae; most similar to the fossil Princeton remains Schweingruber 1978). (Table 1). However, vessel distribution in

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Table 1. Comparison of Prunus allenbyensis to other fossil Rosaceae.

From Hofmann (19441, 19521), Page (19642), Grambast-Fessard (19663), Van der Burgh (19744,19787), Duperon (19765), Wheeler and Matten (1977 6), Wheeler et al. (19788), Süss and Müller-Stoll (19809, 198210), Suzuki (1984 11 ), and Takahashi and Suzuki (1988 12). -PA = parenchyma; H = haltbordered pits, S = and scalariform; v.e. = vessel element, i. v.p. = intervascular pitting.

VESSEL ELEMENTS RAYS PA 11 i f-----1 oe Porosity § c Ii ..s ':;j .~ i!l ..!.l "S. 'a öl'" ·tä ;:: .9 § .S"" öl u ~ ~ " ~ u '" '"~ '"::I ':;j B'" ~ '"oe :§ 1 os .ll! ~ .S '"::I ] c ""oe '" .8 i!l § 'E. ~ '"c ~ .; c c .S ~" ~ .;::: ~ ~ ~ ~ g ""0 .!::l ~ ::I bIJ .,; .c ':;j .g .§ ~ >. § os -5 ~ ~ -5 &l 'E. '" ~ u öl ~ u ':;j" !l .9 g '" .~ e 0 ~ '"~ "0 0 '§ § .~ '3 '"::I '" ~ ..s e E ... Cl .~ i ,e ti ~ ~ 'a ~ C) Vl" Cl Vl ~ Ü P- ~ 8': ~ ~ ~ ;;- ~ P- :;;: Vl ~ ~ Prunus allenbyensis x x x x x x x x x x x x x x x x Pruninium kraeuselii lO x x x x x x x x x x x x x Prunus sp.4, 7 x x x x x x x x H Prunus gumrrwsa 8 x x x x x x x x x x x x x x Prunus iwatense 12 x x x x x x x Prunus palaeozippeliana II x x x x x x x x x x x X A X Prunus ascendetiporulosa II x x x x x x x x x x x x x Prunus uviporulosa II x x x x x x x x x x x x x x Prunus polyporulosa II x x x x x x x x x x x x x Prunoidoxylon multiporosum5 x x x x x x x Lyonothamnoxylon nevadensis2 x x x x x x x x x x x Rosaceoxylon spiraeoides3, 9 x x S x x Sorbus4 x x x x x x Crataegus4 x x x x x x x x x x Pomoxylon l ,7 x x x x x x x x Maloidoxylon galbreathii6 x x x x x x x x Maloidoxylon coloradoense6 x x x x x x x x x x Maloidoxylon castellanense3 x x x x x x x x

the Princeton plant is unlike almost all other Suzuki (1984) described four species of fossil Prunoideae. Semi-ring-porosity, as in Prunus from Kyushu, Japan, as diffuse- the wood of Prunus allenbyensis is only re- porous, but in his description he noted that ported in one other fossil form, Prunoide- latewood vessel elements have a smaller oxylon multisporosum from Agenais, France diameter. This pattern may suggest that the (Duperon 1976). However, this taxon has a woods are semi-ring-porous rather than dif- dendritic vessel arrangement, lacks gum or fuse-porous. His photographs (Suzuki 1984, gum-like deposits and vertical traumatic ducts, figs. 1, 3, 6, 7, 11, and 14) also support this and some vessels have scalariform perfora- interpretation, especially those of P. palaeo- tion plates with a few bars. zippeliana, P. ascendentiporulosa and P. uvi-

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Table 2. Comparison of some features of Prunus gummosa (Wheeler et al. 1989) from Amethyst Mountain, Yellowstone National Park, andP. allenbyensis from Princeton chert 10- cality, British Columbia.

Prunus gummosa Prunus allenbyensis Vessel elements

porosity diffuse sem i-ring solitary, radial multiples, clusters solitary, radial multiples, clusters radial diameter 90 ~m 70 ~m tangential diameter 47 ~m 55 ~m intervascular piuing alternate alternate spiral thickenings present present perforation plates simple simple ray pitting similar to intervascular similar to intervascular tyloses present present dark contents present present

Rays per millimetre 8-17 10 uniseriate: cells tall 10 12 ~m tall 46-185 ~m 37-124 ~m multiseriate: cells tall 5-44 8-40 ~m tall 105-763 ~m 150-630 ~ n-seriate 2-4 2-5 (8) marginal cell rows 1-2 (6) 1-2

Imperl'omte tmcheary elements thin·walled present present circular bordered in radial and tangential walls in radial and tangential walls pils diameter 5 ~m 4 ~m Axial parenchyma apotracheal apotracheal and scanty paratracheal

porulosa. The Japanese material commonly byensis in lacking gum deposits, and vertical has characters absent from the Princeton traurnatic ducts, and having only solitary ves­ plant, including ray structure, and the large sels and half bordered pits in fibres, how­ number of vessel elements in clusters and ra­ ever; as in P. allenbyensis it has scanty para­ dial multiples (Table 1; Suzuki 1984). The tracheal parenchyma. Lower Miocene species, P. iwatense, from Prunus allenbyensis appears to be most Nesori, Japan, is distinct from P. allenbyen­ closely related to the Eocene P. gummosa sis in having circular thick-walled vessel ele­ from Amethyst Mountain, Yellowstone Na­ ments in transverse section with a diffuse­ tional Park (Wheeler et al. 1978). Differences porous pattern, litde or no axial parenchyma, between the woods from these two localities and lacking vertical traumatic ducts (Table 1; are mostly quantitative, and fall within the Takahashi & Suzuki 1988). Prunus sp. from range of variation expected among popula­ the Pleistocene of Tegelen, the Netherlands tions (Table 2; Panshin & De Zeeuw 1980; (Van der Burgh 1974), differs from P. allen- Carlquist 1988). This variation could reflect

Downloaded from Brill.com09/26/2021 11:47:13AM via free access 276 IAWA Bulletin n.s., Vol. 11 (3), 1990 either environmental differenees, or the level different types of Prunus leaves have been ree­ in the tree from whieh the material was deriv­ ognised(Wolfe & Wehr 1988, pers. eomm.). ed. There are differenees in distribution of Conneetion of these isolated organs promise vessels, ray and axial parenehyma, and size to broaden our understanding of these iso­ of individual eells. While the Prineeton wood lated organs as whole plants. is serni-ring-porous, wood from Yellowstone is diffuse-porous. Generally, and within Ro­ Paleoclimatic implications - Eeological saeeae, this type of variation eorrelates with studies based on wood anatomy have shown environmental differenees (Tomlinson & potential in drawing paleoclimatie eonelu­ Craighead 1972; Baas 1973; Bissing 1982; sions (Carlquist 1988; Fahn et al. 1986). Fahn et al. 1986; Carlquist 1988). Seeondly, While many ideas involved in this proeedure rosaeeous wood from both localities is typi­ are still speeulative, it is important to diseuss fied by multiseriate rays with one or two some of the probable funetional-eeologieal rows of marginal eells in mature wood (Table signifieanee of Prunus allenbyensis. 2), although the wood from Yellowstone The presenee of distinet growth rings with may have up to 6 rows of marginal eells narrow vessel elements in latewood may in­ (Wheeler et al. 1978). Thirdly, seanty para­ dieate that the fossil plants grew in a seasonal traeheal parenehyrna is present in the Prinee­ environment. Growth rings have been inter­ ton wood but absent in wood from Yellow­ preted as indieators of some sort of seasonal­ stone. A final differenee between P. allenby­ ity over a long period of time. The relation­ ensis and the Yellowstone wood is vessel ship between growth rings and environment element diameter (Table 2). This differenee is not always straightforward. Although may refleet variation in altitude, latitude, or some taxa develop the same type of growth other eeologieal parameters (Baas 1973; ring under different environmental eondi­ Carlquist 1988). Another possible explana­ tions, others are sensitive indieators of envi­ tion for these differenees is that the Yel­ ronmental ehanges (De Paolis 1948; Bissing lowstone wood was definitely trunk wood 1982; Carlquist 1988). Sinee most wood (Wheeler 1989, pers. eomm.). fragments so far reeovered from the Prinee­ Primary tissues, seeondary phloem, and ton ehert locality have distinet growth rings, periderm are unknown in P. gummosa. Be­ it is most likely that they refleet seasonality. eause primary tissues, seeondary phloem, Seeondly, P. allenbyensis is semi-ring-por­ and periderm are known for P. allenbyensis ous also showing seasonality. and are of taxonomie value and important to Presenee of helical thiekenings in small its diagnosis, we prefer to deseribe it as a vessel elements of latewood may indicate a new species. Further taxonomie eomparison deerease in water availability toward the end between P. allenbyensis and P. gummosa of the growing season. In today's vegetation awaits the diseovery of more eompletely pre­ helieal thiekenings in vessel elements are served sterns of the Yellowstone material widespread in dry areas (Webber 1936; and/or larger speeimens from Prineeton. Carlquist 1966); however, they ean also be Several other rosaeeous remains are known found in areas subjeet to freezing (Carlquist from these loealities. In the Prineeton ehert, 1982, 1984). In addition, helieal thiekenings the rosaeeous flower Paleorosa similkameen­ have been suggested to enhanee water move­ ensis Basinger (1976) has been identified as ment in vessel elements (Jeje & Zimmerman a member of Subfamily Spiraeoideae, Tribe 1979; Carlquist 1988). On the other hand, the Sorbarieae (Cevallos-Ferrlz et al. 1990). helical thiekening has been eorrelated with Three types of Prunus fmits, including endo­ latitude in geographically widespread genera earp and seed, from the Prineeton ehert are like Ilex and Symptocos (Baas 1973; Van der eurrently under investigation. However, at Oever et al. 1981; Baas & Carlquist 1985; the present time the relationship of these or­ Baas & Sehweingruber 1987). gans to the wood is unclear. From eompres­ The wood anatomy of Prunus allenbyen­ sion loealities in the Allenby Formation three sis and the inferred information provided by

Downloaded from Brill.com09/26/2021 11:47:13AM via free access Cevallos-Ferriz & Stockey - Eocene Prunus allenbyensis 277 other plants from the chert (Erwin & Stockey Referenoos 1989), suggest that these plants grew in a mesic environment. Sedimentologic and Baas, P. 1973. The wood anatomical range taphonomic observations of the laminated in Ilex (Aquifoliaceae) and its ecological couplets of Eocene lakes in British Columbia and phylogenetic significance. Blumea 21: suggest the presence of a seasonal climate 193-258. with wet summers and dry winters (Wilson Baas, P. & S. Carlquist. 1985. A compari­ 1988). This interpretation correlates with son of the ecological wood anatomy of the paleobotanical data about the Eocene climate floras of southern California and Israel. (Hopkins et al. 1972). A short winter with IAWA BuH. n. s. 6: 349-364. rare frost periods has been postulated by Baas, P. & F.H. Schweingruber. 1987. Eco­ Basinger (1976). Warm temperatures during logical trends in wood anatomy of trees, the Princeton chert deposition are inferred shrubs, and climbers from Europe. I AWA from fossil plants with extant relatives living BuH. n.s. 8: 245-274. under these conditions (e.g., Arecaceae, Ara­ Barghoorn, E.S. 1940. The ontogenetic de­ ceae). velopment and phylogenetic specialization The plant assemblage so far known from of rays in the xylem of dicotyledons. I. the Princeton chert suggests the presence of Primitive ray structure. Amer. I. Bot. 27: two distinct, but nearby, environments in the 918-928. sedimentary basin. Aquatic and semi-aquatic Barghoorn, E.S. 1941a. The ontogenetic de­ plants like Keratosperma (Araceae), Heleo­ velopment and phylogenetic specialization phyton (Alismataceae), Allenbya (Nymphaea­ of rays in the xylem of dicotyledons. H. ceae), Eorhiza (incertae sedis), and Decodon Modification of multiseriate and uniseriate (Lythraceae) are most common. A second rays. Amer. I. Bot. 28: 273-282. group of plants not closely related to the Barghoorn, E.S. 1941b. The ontogenetic de­ aquatic system includes Ampelocissus (Vita­ velopment and phylogenetic specialization ceae), and Liriodendroxylon (Magnoliaceae). of rays in the xylem of dicotyledons. III. Prunus allenbyensis should be added to this The elimination of rays. BuH. Torrey Bot. second group. This terrestrial component of Club 68: 317-325. the Princeton chert may include important Basinger, I.F. 1976. Paleorosa similkam­ angiospermous plants of the coniferous for­ eenensis gen. et sp. nov., permineralizect est that surrounded the lakes of the area. flowers (Rosaceae) from the Eocene of British Columbia. Can. I. Bot. 54: 2293- Acknowledgements 2305. This work was supported in part by Basinger, I.F. & G.W. Rothwell. 1977. NSERCC (Natural Sciences and Engineering AnatomicaHy preserved plants from the Research Council of Canada) grant A6908 to Middle Eocene (AHenby Formation) of R.A.S. Thanks are given to Consejo Nacio­ British Columbia. Can. I. Bot. 55: 1984- nal de Ciencia y Tecnologia (CONACYT) of 1990. Mexico for financial support to S.R.S.C.F. Bastin, E. S. 1895. Structure of our cherry We thank Dr. Elisabeth A. Wheeler, North barks. Amer. I. Pharm. 67: 435-452. Carolina State University, Raleigh, for her Bissing, D.R. 1982. Variation in qualitative valuable comments on the manuscript and anatomical features ofthe xylem of select­ examination of specimens, and Dr. Sherwin ed dicotyledonous woods in relation to Carlquist, Rancho Santa Ana Botanic Garden water availability. BuH. Torrey Bot. Club and Pomona College, for helpful discussion 109: 371-384. and examination of the fossil specimens. Boneham, R.F. 1968. Palynology of three This study is submitted in partial fulfill­ Tertiary coal basins in south central Brit­ ment of the requirements for the degree of ish Columbia. Ph.D. thesis, University of Doctor of Philosophy, Department of Bot­ Michigan, Ann Arbor, MI. any, University of Alberta.

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