A Permineralized Flower from the Middle Eocene of British Columbia'
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Amer. J. Bot. 74(12): 1878-1887. 1987. A PERMINERALIZED FLOWER FROM THE MIDDLE EOCENE OF BRITISH COLUMBIA' RUTH A. STOCKEY Departmentof Botany, University of Alberta,Edmonton, Alberta T6G 2E9, Canada ABSTRACT A permineralizedflower bud, two stamen clustersand one isolated stamen of similar mor- phology have been found in the black cherts of the Middle Eocene Allenby Formation of Princeton,British Columbia. Specimenswere studied using a modified cellulose acetate peel technique and hydrofluoricacid. The single flower specimen, 4.5 mm long and 4.0 mm in diameter,represents half of a relativelymature bud of a bisexualflower with a superiorovary. The two-loculatepistil is 2.5 mm long with a solid style and a lobed stigmatic surface.No ovules have been observedin attachment.Twenty-two to 24 stamensare borne in threewhorls or a tight helix. Pollen sacs of the anther are elongate with a thin connective while filaments are laminar.Anther walls containrectangular cells with darkcontents that also can be identified in isolated stamensor stamenclusters. Abundant stephanocolpate (pentacolpate), psilate pollen grains 20 ,umin diameterhave been isolated and examined using scanningand transmission electronmicroscopy. Grains are tectate,columellate with a broad foot layerthat thins near the apertures,and an endexineof small platelets.The remainsof four petalsare surroundedby one largesepal, suggestingtwo in the whole flower.Morphological features of this flowerare com- parableto taxa of the Flacourtiaceaeand Papaveraceae,but show closest similaritiesto the Eschscholziaeaeof the Papaveraceae.Difficulties with reconcilingthe placementof this flower in the Eschscholziaeaeand the known environmentof deposition of the Princetonchert are discussed.The fossil materialrepresents a new angiospermoustaxon: Princetonia allenbyensis Stockeygen. et sp. nov., family Incertaesedis. PERMINERALIZED vascular plants from the series of studies currently underway in our lab- Princeton chert locality in British Columbia oratory of the Princeton flowering plant re- have been described by various authors since mains and is based on a silicified flower bud the 1970's (Miller, 1973; Robison and Person, and several isolated floral parts of well-pre- 1973; Basinger, 1976; Basinger and Rothwell, served specimens with in situ pollen. 1977; Rothwell and Basinger, 1979; Basinger, 1981; 1984; Stockey, 1984). Most of these MATERIALS AND METHODS-One perminer- studies have dealt with fossil conifers; how- alized flower bud, two stamen clusters and one ever, the angiosperm remains have been just isolated stamen of similar morphology have briefly mentioned (Basinger and Rothwell, been found in chert blocks near Princeton, Brit- 1977). Only a dicotyledonous rhizome of un- ish Columbia. Specimens come from the east known affinities, Eorhiza arnoldii Robison and side of the Similkameen River, 8 km south of Person (1973) and a rosaceous flower, Paleo- the town of Princeton. The locality has been rosa similkameenensis Basinger (1976) have referred to as locality "I" (Boneham, I 968) and been described in any anatomical detail. the "Princeton chert" (Basinger and Rothwell, Surveys of all 49 layers of the Princeton chert 1977; Stockey, 1984). Chert deposits are part indicate an abundance of flowers, fruits, seeds, of the Princeton Group, Allenby Formation wood, and foliage from various angiosperm and are located 630 m above the Princeton- families. The present report is the first in a Black coal seam (Boneham, 1968). The Prince- ton Group has been dated as Middle Eocene by Wilson (1977, 1982) studying freshwater I Received for publication 27 October 1986; revision fish and Hills and Baadsgaard (1967) using accepted 24 March 1987. K-Ar dates. This work was supported in part by NSERCC (Natural Sciences and Engineering Research Council of Canada) All chert blocks were cut into slabs and stud- Grant A6908. ied using a modified cellulose acetate peel tech- I thank Dr. Daniel J. Peteya, University of Alberta, for nique and hydrofluoric acid (Basinger and technical assistance in transmission microscopy; Mme. M. Rothwell, 1977; Basinger, 1981). Peel sections Van Campo, Universite des Sciences et Techniques du Languedoc, Montpellier, for making the Layka theses were mounted in Coverbond xylene soluble available; Helen Ko for photographic assistance; and George mounting medium for microscopic examina- Fabi, University of Alberta, for reconstructions. tion. Fifty-one consecutive sections were made 1878 December 1987] STOCKEY-PERMINERALIZED EOCENE FLOWER 1879 of the holotype to enable three-dimensional sexual actinomorphic flower with a superior reconstruction (Fig. 24, 25). ovary (Fig. 1). However, no ovules have been Scanning electron microscopy of pollen in observed in any sections. Although the pistil the anthers was done using the back side of is not seen in attachment it is clearly in the deeply-etched peels. Peel sections were mount- right position for a hypogynous flower (Fig. 1). ed on stubs with double-sided tape, covered The pistil measures 2.5 mm long and was ap- with 150 A Au on a Nanotek Sputter Coater parently composed of two carpels (Fig. 1, 3). and viewed at 20 kV with a Cambridge Stereo- Consecutive sections reveal no further parti- scan 250. tioning of the pistil. In further sections (Fig. 3, One small peel section was demineralized in 4) the style is seen to be solid, 0.7 mm long, concentrated hydrofluoric acid and washed with and ends in a constricted region and an ex- several changes of distilled water. The acetate panded stigmatic surface that appears to be matrix was then dissolved in several changes slightly lobed (Fig. 1, 2). of acetone. Pollen grains and floral debris were The perianth is biseriate and parts are free embedded in Spurr's (1969) resin. Sections were from one another. Remains of one sepal are cut with a diamond knife and collected on present (Fig. 1, 3, 6) and enclose one entire formvar-coated grids and viewed with a Phil- side of the flower bud (Fig. 5, 7, 8). The sepal ips EM 200 at 60 kV for transmission electron can be distinguished from petal remains by its microscopy. darker, more compact cells and the presence Comparison of floral morphology with that of scattered swollen areas (Fig. 5, 7, 8). The of extant families was done using the data set exact nature of these areas, 0.2 mm in diam- of Hansen and Rahn (1969, 1972) with the eter, is unknown; they perhaps represent glands MEKA 1.1 program provided by T. Duncan or possible damage by fungi or insects (pre- or and C. A. Meacham, University Herbarium, postburial). Due to the concave nature of floral University of California, Berkeley. parts and based on size and appearance of this sepal, there were probably two sepals in a com- Diagnosis-Princetonia allenbyensis Stock- plete flower. Cells of the sepal are generally ey gen. et sp. nov. Bisexual, bud of an acti- crushed and not easily discernible. nomorphic flower, 4.5 mm long by 4.0 mm in Portions of three petals are present in the diameter, with superior ovary. Pistil 2.5 mm bud (Fig. 1, 3, 6). One concave petal is observed long with two carpels; style solid, 0.7 mm long in a near paradermal section (Fig. 8) and is with expanded, lobed stigmatic surface. Bise- broken but nearly complete as is seen in con- riate perianth with free parts; two sepals, four secutive sections (Fig. 5, 7). Sections of two petals. Stamens numerous (at least 24), in three other petals are seen in near median longitu- whorls or a tight helix; filaments laminar, 0.7 dinal sections of the flower. Based on floral mm long. Anthers elongate, 2.5 mm long with symmetry, four petals probably occurred in the slender connective and four widely separated complete flower. Vascular tissue is preserved pollen sacs; rectangular cells with dark contents in the petals (Fig. 2, 4, 6) and in longitudinal in walls of pollen sacs. Pollen 20 ,um in di- sections the tracheids exhibit scalariform pit- ameter, elliptical, pentacolpate, psilate, tectate, ting (Fig. 14). Petals are composed of nearly columellate exine with thin platelets of endex- isodiametric parenchymatous cells 30 ,um in ine, reduced to a thin foot layer at apertures. diameter and reach 10 cells in thickness in the Etymology: The generic name is based on basal regions (Fig. 4, 8). the locality, the Princeton chert, the specific Stamens are numerous and, due to the con- epithet on the nearby abandoned mining town cave nature of the enclosing floral parts, were of Allenby. difficult to count. Color coding of anthers in Holotype specimen no. P2152 A and para- camera lucida drawings allowed reconstruction types P1631 B bot, P2604 C bot, P3204 C bot, of 22 stamens with small portions of two oth- D top, E, and P3336 B top are housed in the ers. Isolated clusters of stamens of identical University of Alberta Paleobotanical Collec- morphology (Fig. 10, 11) also reveal 24-27 tion (UAPC-ALTA). stamens per cluster. Stamens appear to be borne in three whorls or a tight helix (Fig. 6) and Description - The holotype specimen is one probably dehisced longitudinally. Filaments half of a relatively mature flower bud (Fig. 1). are laminar (Fig. 2) and 0.7 mm long. Anthers Although the initial saw blade cut passed are very elongate (Fig. 5, 9), up to 2.5 mm, and through the center of the bud, pistil and re- anther sacs are adnate to a slender connective. ceptacle are still visible in the first few sections This attachment makes the four anther sacs (Fig. 1, 3). The bud measuring 4.5 mm long appear widely separated in transverse sections and 4.0 mm wide apparently represents a bi- (Fig. 5, 10, 11, 25). Walls of the pollen sacs 1880 AMERICAN JOURNAL OF BOTANY [Vol. 74 are composed of small rectangular cells with from one another; 109, anthers more than 10, dark contents (Fig. 16). These cells are easily fertile; 116, anthers opening by longitudinal distinguished in the chert in the isolated sta- slits; 120, stamens free from the corolla; 122, mens and stamen clusters (Fig.