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Paleobotany |
2School of Life Sciences Faculty and Administration, Arizona State University, PO Box 874501, Tempe, Arizona 85287-4501 USA; 3Department of Biological and Environmental Sciences, Georgia College & State University, Campus Box 081, Milledgeville, Georgia 31061 USA
Received for publication February 18, 2004. Accepted for publication September 30, 2004.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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4.6 mm long x 1.9 mm wide, with a small, triangular embryo cavity and a prominent distal wing. The inflated wing is filled with a bilobed parenchymatous pad of tissue with a central cavity. Shirleya grahamae is assigned to the Lythraceae, and is most similar to Lagerstroemia, based on the synapomorphies of distally winged seeds and revolute cotyledons. Shirleya differs from Lagerstroemia in seed arrangement, and pericarp and wing anatomy. This study provides the first anatomical information about a Miocene Lagerstroemia-like fruit and documents further diversity of the Lythraceae in the Neogene of northwestern North America.
Key Words: fossil fruit • Lagerstroemia • Lythraceae • Miocene • permineralization
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Graham et al., 1993a
; Judd et al., 2002
). The family includes both Old World and New World trees, shrubs, perennial herbaceous plants and annual herbaceous plants. They occur primarily in mesic to wet habitats including mangroves, rainforests, and marshes. Both broad and narrow circumscriptions of the family have been proposed. Older literature, including monographic work by Koehne (1881–1886
, 1885
, 1903
), recognized the Lythraceae sensu stricto and placed several closely related genera into their own separate families: Sonneratia L. and Duabanga Buc.-Ham. within the Sonneratiaceae; and the pomegranate, Punica L. within the monotypic Punicaceae. Recent phylogenetic analyses have recognized a broader monophyletic group including these genera and Trapa L. (formerly within its own monogeneric family, Trapaceae) in the Lythraceae sensu lato. The position of Trapa within the Lythraceae is a surprising result, as this genus has traditionally been difficult to place because of extensive autapomorphic features (Dahlgren and Thorne, 1984
; Johnson and Briggs, 1984
; Graham et al., 1993a
, b
; Graham, 1999
; Shi et al., 2000
; Huang and Shi, 2002
). The most complete phylogenetic analysis to date (S. Graham et al., unpublished data), based on combined morphological and molecular data, supports these results (S. Graham, Missouri Botanical Garden, personal communication).
The Lythraceae has an extensive fossil record that includes both extant and extinct genera (Tiffney, 1981
). Decodon Gmelin., the most commonly known taxon, is found as permineralized fruits, roots, and stems from the middle Eocene Princeton chert of British Columbia (Cevallos-Ferriz and Stockey, 1988
; Little and Stockey, 2003
), fruits and seeds from the middle Eocene Clarno Nut Beds of Oregon (Manchester, 1994
), seeds and young twigs from the Miocene of Nevada (Bertram, 1998
; K. Pigg, unpublished data), and isolated seeds from Europe, Russia, North America, and Japan (Dorofeev, 1963
; Tiffney, 1981
, 1994
; Friis, 1985
; Matsumoto et al., 1997
). Compressed specimens showing fruits in attachment to twigs bearing Decodon leaves have recently been described from the Miocene of Bohemia (Kva
ek and Sakala, 1999
). These authors also review the compression record for Decodon. Extinct lythraceous genera, based on fossil seeds and fruits, are known from the Campanian of Mexico (Rodriguez-de la Rosa et al., 1998
), the London Clay, and other Tertiary sites in Russia, England, Denmark, Germany, the Czech Republic and North America (Dorofeev, 1963
; Tiffney, 1981
; Friis, 1985
; Mai and Walter, 1985
). The older literature describing these occurrences was reviewed by Tiffney (1981)
. Lythraceous seeds compared to Lawsonia L. and leaves similar to Duabanga are known from the Princeton chert (Cevallos-Ferriz and Stockey, 1988
; Little and Stockey, 2002
). Fossil fruits assigned to Punica are known from the Neogene of Europe (Mai, 2001
). Other seeds of unclear generic affinity occur in the Eocene Quilchena flora of British Columbia (Mathewes, 2003
).
Fruits assigned to Lagerstroemia L. occur in the Neogene and Pleistocene of Japan, the last of which has been compared with the extant Chinese species L. indica L. (Miki, 1936
, 1937
). Fossil leaves attributed to Lagerstroemia have been described from India (Trivedi, 1956
) and the Oligocene of Japan, with the Japanese specimens compared with the ornamental species L. indica of central China and L. speciosa (L.) Pers. of India (Tanai and Uemura, 1991
). Enigmocarpon Sahni and Rode, a silicified fruit from the Indian Deccan Intertrappans, and Sahnianthus Shukla, thought to be the flower of the same plant, are usually considered to be lythraceous (Rode, 1933
; Sahni and Rode, 1937
; Sahni, 1943
; Shukla, 1958
). Trapa has an extensive fossil record in Asia, North America and Europe (Manchester, 1999
).
Fossil lythraceous wood (Mädler, 1939
; Prakash, 1965
, 1971
; Srivastava and Bande, 1990
; Little and Stockey, 2003
) and pollen (Graham and Graham, 1971
; Muller, 1981
) are also components of many Tertiary floras, with Cuphea P. Browne pollen particularly well represented. Pollen of Lagerstroemia found in Pleistocene interglacials of Honshu, Japan has been correlated with the warmer time intervals (Miyoshi et al., 1999
; Fujiki et al., 2001
).
In the present study, we describe a newly recognized silicified fruit, Shirleya grahamae Pigg & DeVore gen. et sp. nov., from the middle Miocene Yakima Canyon of central Washington State, USA. The description of S. grahamae is based on permineralized, loculicidal capsules possessing persistent floral tubes with reflexed calyx lobes, seeds with distally elongate wings, some containing mature embryos with revolute cotyledons, and capsule valves from dehisced fruits. Shirleya fits well within the Lythraceae, and is most similar to the crepe myrtle, Lagerstroemia, with which it is compared in detail. Whereas Shirleya shares with Lagerstroemia the synapomorphies of a distal and revolute cotyledons, features of the seed wing, fruit wall, and positioning of seeds in the fruit differ. The description of S. grahamae documents a distinctive anatomically preserved plant with Lagerstroemia-like features and substantially expands the fossil record of the Lythraceae in the Neogene of northwestern North America.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Borgardt and Pigg, 1999
). Re-evaluation of the outcrop demonstrates that the blocks of silicified plants are found within voids and cravasses in the basalt flow and not within an interbed (William C. Rember, University of Idaho, personal communication). Additional study suggests that the stratigraphic position may be within the Wapanum Basalt and therefore somewhat younger than previously thought (Steven P. Reidel, Pacific Northwest National Laboratory, Richland, Washington, personal communication). Clearly, silicified plant remains must represent a flora that is not contemporary with the basalts it is found in. Currently, we are lacking a clear picture of the depositional environment of the fossil remains and that limits determining a highly constrained age for the flora itself. We can say that the flora is younger than the surrounding basalt; however, we are not certain how much older it is than the next cycle of basalt deposition. Specimens are housed as part of the Tuggle/Foisy Collection in the Burke Museum of Natural History and Culture, University of Washington, Seattle (UWBM) and in the Fossil Plant Collections, Arizona State University, Tempe (ASU). Some fossil fruits were sectioned serially into thin wafers at very close intervals of less than 0.5 mm on a Microslice annular saw (MR Semicon, Albuquerque, New Mexico, USA); others were cut on a Buehler Isomet Low-Speed saw (Lake Bluff, Illinois, USA) into wafers 0.5–1.5 mm thick. Sections were mounted onto microscope slides with either epoxy or UV-cured adhesive (UV-154, T.H.E. Company, Lakewood, Colorado, USA) with coverslips mounted in xylene-soluble Permount adhesive (Fisher Scientific, Fair Lawn, New Jersey, USA), and studied with mostly reflected light. A few selected sections were ground thin enough to study with transmitted light microscopy. Comparative material of extant Lagerstroemia and Sonneratia was prepared both by hand sectioning and by standard histological techniques. Original observations of Lagerstroemia fruit and seed development (Figs. 3, 4, 6, 9– 11, 14–16, 30–31, 36) are included as part of the discussion.
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). Complete ontogenetic sequences cannot be fully resolved in fossil seeds because not all developmental stages are known and some layers may not be completely preserved. For this reason we are reluctant to use these terms and instead characterize the seed coat of Shirleya descriptively. |
RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Generic diagnosis
Fruit a capsule surrounded by persistent floral tube with reflexed calyx lobes; placentation axile, dehiscence loculidical, ovary superior, locules 5–7, crowded with distally winged, anatropous seeds, 5–7 mature and several smaller seeds per locule, each with small triangular embryo cavity proximally, separated by deep transverse groove from prominent distal wing comprising up to 2/3 of seed length; wing filled with bilobed parenchymatous tissue with central cavity; seeds subapically attached and pendant in fruit, curving basally and radially; embryos with revolute cotyledons.
Species
S. grahamae Pigg & DeVore sp. nov.
Species diagnosis
Fruit 10.0 mm long x 11.5–12.5 mm wide, with mesocarp 0.8–1.0 mm thick, pericarp two-zoned, outer rind 0.4 mm thick of small cuboidal cells, inner zone of parenchymatous tissue with sclereid nests; dehiscence slit narrow if present, attachment of seeds to placenta narrow, central axis 1.0 mm diameter, stellate with broad parenchymatous pith; primary xylem with helical and scalariform wall thickenings; small zone of secondary xylem present; seeds up to 4.6 mm long x 1.9 mm wide, integument with innermost layer 4–5 cells thick of parenchymatous cells, surrounded by zone of 10 cells thick of tangentially elongate sclereids that grade into 3–5 layers of isodiametric sclereids, surrounded by a uniseriate palisade layer.
Holotype
UWBM 55134 (Figs.1, 2, 8, 17–21, 23, 27–29, 34), deposited at the Burke Museum of Natural History and Culture, Seattle.
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Type locality
The "Hi Hole," one of the "County Line Holes," approximately 11.2 km north off Interstate 82, Firing Center Exit, Yakima County, on Yakima River Canyon Road (Pomona Quadrangle, T14N, R19E, NE1/4 of NW 1/4 of Sec. 3), Washington State, USA.
Age and stratigraphy
Middle Miocene, Columbia River Basalt Group.
Etymology
Shirleya grahamae is named in honor of Dr. Shirley A. Graham for her many significant contributions to the study of the family Lythraceae.
Description
The description of Shirleya grahamae is based on silicified specimens of several young fruits, one studied in detail, fourteen mature fruits, and ten fragments of capsules from dehisced fruits. Some specimens have weathered out of the rock matrix and are preserved in the round (Figs. 1, 2, 5, 8, 17–21, 23, 27, 29), but most occur within the rock matrix (Figs. 7, 12, 13, 22, 24–26, 32–35). Together, these specimens provide details of morphology, anatomy and three-dimensional organization of fruits, seeds, embryos and dehisced fruits. Fruits show evidence of a persistent floral tube with reflexed calyx lobes (Figs. 2, 7, 13, 22). At maturity, capsules are fractured loculicidally, resulting in fragments of two adjacent half-locules and their common septum (Figs. 5, 25).
Fruits are smooth, subglobose capsules up to 10 mm long and 11.5–12.5 mm wide (Figs. 1, 2). Five to seven locules are radially arranged around a central axis and obovate in transverse section, broadest toward the periphery (Figs. 8, 17–21). Locules are 0.8 mm wide tangentially to the inside and up to 3 mm wide tangentially to the periphery and up to 7.0 mm wide radially. In some specimens a thin central dehiscence slit occurs in the outer locule (Fig. 25), in others they are less conspicuous prior to dehiscence. The central fruit axis 1.0 mm in diameter and composed of a star-shaped eustele with a broad parenchymatous pith surrounded by a small amount of secondary tissue that appears as a continuous line (Figs. 20, 21). Within the fruit axis, primary xylem elements have helical and scalariform wall thickening patterns. It is not clear whether the vascular bundles are bicollateral as is typical in Myrtales. As in extant Lagerstroemia (Fig. 15), the central axis is narrowly connected to carpels (Figs. 8, 18–21) and is free from the septa upon dehiscence.
The pericarp of Shirleya is 0.8–1.0 mm thick with a narrow outer rind 0.4 mm thick, of small parenchymatous cells packed closely together (Figs. 7, 26). The inner pericarp is made up of parenchymatous tissue containing small clusters of sclereids throughout (Figs. 23, 27), and approximately a dozen parenchymatous cells radiate from each sclerotic nest. Vascular strands have also been observed in various planes of section (Fig. 27). Within the locule, an inner region 4 cells thick of small cells occurs adjacent to the seeds (Fig. 26).
As in Lagerstroemia (Figs. 11, 14, 15), in Shirleya there are 5–7 mature, tightly-packed seeds per locule, and sometimes several smaller seeds with similar morphology (Figs. 7, 8, 17–21, 25, 35). Anatropous seeds are attached subapically and narrowly along the central axis, hanging pendulously within the fruit with the wings curved to extend out radially from the axis (Fig. 7). Seeds are up to 4.6 mm long x1.9 mm wide, with a small, triangular embryo cavity proximally separated by a deep transverse groove from an elongate, distal wing that comprises up to 2/3 of the seed length (Figs. 7, 8, 17–21, 31). They vary in shape in relation to their position in the locule. Seeds have a small tail or hook on both their proximal and distal ends (Figs. 20, 21, 24, 25). The micropyle is present on the apical end of the anatropous seed and is slightly asymmetric (Fig. 34).
The seed coat is composed of an innermost layer 4–5 cells thick of parenchymatous cells lining the embryo cavity surrounded by a zone of 10 tangentially elongate sclereids. This layer grades into a region of cells 3–5 layers thick of isodiametric sclereids that is surrounded by a uniseriate palisade layer (Figs. 24, 25, 28). Within each wing is a large, bilobed pad of parenchymatous tissue with a central cavity (Figs. 8, 17– 21, 29). Several seeds possess embryos with revolute cotyledons which appear in serial section as several concentric rings of tissue (Figs. 32, 33). A small fruit of Shirleya is 3.5 mm long x1.8 mm wide. This specimen shows an attached floral tube and within the gynoecium remnants of several ovules that are attached to the placenta and positioned at right angles to the floral axis (Figs. 12, 13).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Among the most taxonomically important of these are: (1) a superior ovary; (2) a variable number (5–7) of locules, (3) seeds crowded into locules, resulting in variable seed shape, (4) axile placentation, (5) a persistent floral tube with reflexed calyx lobes, and (6) seeds with a highly sclerotic seed coat (S. Graham, Missouri Botanical Garden, personal communication). Other characters shared with some lythraceous genera include loculicidal dehiscence, more than five locules, several to many seeds per locule, variability in seed shape, presence of a wing, and a central axis persisting separately when the capsule valves fall back (W. Judd, Florida Museum of Natural History, personal communication).
Shirleya is most similar to the crepe myrtle, Lagerstroemia (Figs. 1–6). Both have distally winged seeds and embryos with revolute cotyledons, synapomorphies in the Lythraceae (Figs. 30–33; Corner, 1976
; Graham et al., 1993a
). Shirleya fruits are of comparable size to those of many Lagerstroemia species (10–12 mm long x 6–8 mm wide), although a few species of Lagerstroemia have more robust fruits over 4 cm long (e.g., L. macrocarpa Kurz, Figs. 6, 15; Furtado and Srisuko, 1969
; Gardner et al., 2000
). Also, seeds in both genera are tightly packed and nested in an overlapping fashion within each locule (Figs. 7, 10, 11). In addition to these similarities, however, we believe the differences between the two taxa justify the designation of the new genus Shirleya for the Yakima Canyon fossils. The major differences are in (1) pericarp thickness and histology; (2) positioning of seeds within the fruit; and (3) anatomy of the wing. As in most of the Lythraceae, fruits of Lagerstroemia are typically thin-walled capsules (Figs. 3, 4, 6). In contrast, in Shirleya the pericarp is somewhat thicker (Figs. 7, 8, 17–21). The pericarp of Shirleya is composed of two major zones (Figs. 7, 22, 26): an outer small-celled zone and an inner parenchymatous tissue comprised of groups of thin-walled cells radiating around embedded clusters of sclereids (Figs. 23, 26, 27). Anatomically, it somewhat resembles the berry-like fruits of Sonneratia (Duke and Jackes, 1987
), Duabanga, and the Indian fossil Engiomocarpon (Mahabale and Deshpande, 1957
). However, like most Lythraceae, Shirleya is dehiscent, as evidenced by dehiscent slits in some specimens (Fig. 25), and by dehisced valves of others (Fig. 5).
A second difference between Shirleya and Lagerstroemia is in seed positioning within the fruit. In developing gynoecia that we dissected from unopened floral buds of Lagerstroemia, the ovules are attached at right angles to the floral axis and along its length (Fig. 9). At this stage the wing is only slightly evident as a narrow flange along the dorsal edge of the ovule (K. Pigg, personal observation). A similar, slight flattening on the raphe side also occurs in developing ovules of Ammannia L., Nesaea Comm. ex Kunth., Woodfordia Salisb. and Sonneratia (Joshi and Venkateswarlu, 1936
), although these genera lack a distal wing. As Lagerstroemia seeds develop, the seed bodies enlarge and the wings become more elongate, resulting in seeds becoming nested and overlapping within the confines of the locule. In both young and mature fruits of Lagerstroemia seeds are borne mostly upright within the fruit, with the seed bodies at the base and the elongate wings filling the upper part of the fruit (Figs. 10, 11).
The young fruit of Shirleya is similar to mature fruits, with a persistent floral tube, peduncle, and generally similar ovary shape (Figs. 12, 13). Within the ovary there are structures attached to the central axis that are oriented in essentially the same manner as those in the Lagerstromeia gynoecium (Figs. 9, 12). We interpret these structures to be remnants of ovules at a similar or slightly later stage of development than the illustrated Lagerstroemia gynoecium (Figs. 9, 12). As the fruits develop in Shirleya, seeds remain attached apically on the floral axis and hang pendulously. The distal wings are displaced proximally and curve downward and out radially, resulting in a quite different orientation in comparison with the upright seeds of Lagerstroemia (compare Figs. 7, 11).
Shirleya and Lagerstroemia both have distally elongate wings, a synapomorphy within the family, but they differ in their structure. Initially, in freshly dissected seeds of Lagerstroemia that we studied the wings are thin and flattened (Fig. 11). However, in order to try to simulate the conditions of an aquatic depositional environment encountered by Shirleya seeds, we soaked Lagerstroemia seeds in water for several days. Upon hydration, the seeds became waterlogged and the wings inflated. An individual inflated wing of extant Lagerstroemia is elongate-triangular in transverse section, with a solid core of parenchymatous tissue surrounding a single vascular strand (Fig. 16). In contrast, seeds of Shirleya, which would also have become waterlogged prior to fossilization, have wings that are laterally expanded and bowed out, surrounding a central cavity (Figs. 8, 17–21, 29).
Shirleya differs from other members of the Lythraceae in additional characters. Although loculicidal dehiscence occurs in Decodon and Heimia, these genera have thin-walled capsules that bear numerous, pyramidal seeds with spongy, parenchymatous tissue and a distinct germination valve (Tiffney, 1981
; Cevallos-Ferriz and Stockey, 1988
; Takhtajan, 1996
; Matsumoto et al., 1997
). In contrast, the distally winged seeds of Shirleya have a mostly sclerotic seed coat around the seed body. Dehiscence in Pehria Sprague is also loculicidal with elongate, obovoid seeds. Rotala L. has septicidal dehiscence, while in Ginoria Jacq. and Tetrataxis Hook. dehiscence is septifragal, and in Lythrum L. dehiscence occurs both septicidally and septifragally (Graham et al., 1993a
). In Nesaea the capsule is initially circumscissle through an operculum, and then irregular in dehiscence, Crenea Aublet., Adenaria Kunth., and Didiplis Raf. have small indehiscent fruits. Lafoensia Vand., a New World genus, has woody capsules with loculicidal dehiscence and bilaterally compressed seeds. Hionanthera Fernandez & A. Diniz., a genus endemic to Mozambique, has capsules with relatively few, large seeds. Seeds of Koehneria Graham, Tobe & Baas, a genus from Madagascar, are 1.2–1.3 mm long x 0.9–1.0 mm wide, and conical with a broad chalazal end (Graham et al., 1986
). Seeds of Lawsonia are irregularly obpyramidal and have a spongy apex of large mesotestal cells (S. Graham, Missouri Botanical Garden, personal communication). Sonneratia seeds lack wings and the embryo is straight to slightly curved, but the cotyledons are not revolute like those of Lagerstroemia and Shirleya (Duke and Jackes, 1987
). Duabanga seeds are cylindrical with both a distal and an apical flange or wing (Venkateswarlu, 1937
), while Punica, the pomegranate, is unique among this group in the presence of a juicy sarcotesta that comprises the outermost seed layer (Dahlgren and Thorne, 1984
; Graham et al., 1993a
). Trapa, the water chestnut, is most distinctive, with a spiny fruit containing a single seed (Dahlgren and Thorne, 1984
).
In contrast to the distally elongate wings on seeds of Shirleya and Lagerstroemia, a thin circular flange, sometimes also referred to as a wing, may occur in Physocalymma Pohl., Diplusodon Pohl., Crenea, Lafoensia Vand. and Cuphea P. Browne (Graham et al., 1986
, 1993). Seeds of Lythrum, Nesaea, Ginoria, Ammannia, Didiplis Raf. and Duabanga are numerous and tiny. Woodfordia Salisb. has elongate seeds with unusual spiral trichomes. The zygomorphic flowers of the speciose genus Cuphea form fruits that open and exend the placenta and attached seeds through a slit in the capsule wall at maturity, and thus are quite unlike Shirleya in overall form and function.
Shirleya is also distinct from previously known fossil fruits assigned to the Lythraceae. Fruits from the Neogene of Japan assigned to Lagerstroemia are of similar size but the lack of internal anatomy limits detailed comparisons with Shirleya (Miki, 1936
, 1937
). Decodon is a smaller fruit about half the size of Shirleya (5 mm long x 3–4 mm wide) with 4–6 locules and a thin pericarp and equally thin septa, up to 12–18 small pyramidal seeds per locule. These seeds are 1.2 mm long x 0.7 mm wide with a large amount of spongy tissue, a prominent germination valve, and a straight embryo (Cevallos-Ferriz and Stockey, 1988
). Enigmocarpon seeds are structurally similar to Decodon but over three times as long (3 mm; Sahni, 1943
; Cevallos-Ferriz and Stockey, 1988
). This fruit is larger (18 mm long x 14 mm wide) and more robust than both Decodon and Shirleya (10 mm long x 11.5–12.5 mm wide), bears 18 seeds per locule, usually eight locules, and has a thick pericarp (2–3 mm thick) and thin septa, resulting in prominent dehiscence slits. It may be that because Shirleya fruits have pericarp walls and septa of more equal thickness (0.8–1 mm), the mechanical stress upon dehiscence is less and, thus, the dehiscence slits, although present (Fig. 25) are less well defined. Enigomocarpon has seeds borne in two obvious rows, a feature we did not see in Shirleya. The presence of a chalazal thickening of the nucellus, the hypostase, and apical prolongation into an epistase have been discussed in Enigmocarpon and Sonneratia (Sahni, 1943
; Mahabale and Deshpande, 1957
) and a hypostase occurs in Decodon (Cevallos-Ferriz and Stockey, 1988
). These structures are not evident in Shirleya.
Structure/function and paleoecological implications of Shirleya fruits
Because of the nature of fossil occurrence at the Yakima Canyon locality, it would be difficult to study the flora containing Shirleya taphonomically. Nevertheless, the three closely located "County Line Holes" differ compositionally. The "Hi Hole" is rich in seed and fruit remains (Shirleya, Liquidambar, Quercus, Nyssa, cf. Paliurus, Borgardt and Pigg, 1999
; Tcherepova, 2001
; Pigg et al., 2004
), as well as smaller twigs (e.g., Quercus, Vitis). The "Lo Hole" is composed primarily of taxodiaceous conifer wood and foliage, roots, fern rhizomes, and fragments of fern and dicot foliage, roots and fragmentary dicot wood (Pigg and Rothwell, 2001
; Coleman, 2004
). The "Ho Hole" contains almost exclusively wood remains with damage patterns, and has not yet been studied. The sorting seen in these remains is consistent with zonation that occurs in modern swamp and other wetlands environments. For example, in bald cypress swamps today there can be fairly abrupt changes in vegetative composition from lower to higher elevation within a few meters. Lower elevations are characterized by submerged Taxodium trunks with "knees" that are closely associated osmundaceous and other ferns on growing hummocks (K. Pigg, M. DeVore, personal observation). On slighty higher ground the associated hardwoods such as Liquidambar, Nyssa, Quercus, and vitaceous vines occur (Pigg and Rothwell, 2001
).
Like the fruits of Lagerstroemia, Shirleya fruits are loculicidal capsules that fragment upon dehiscence and separate completely from the central axis. In the modern crepe myrtle genus, opened fruits often remain held together by a persistent floral tube and the fruits are often retained on branches of the parent plant (K Pigg, M. DeVore, personal observation). As the branches are blown around by wind currents, the seeds are shaken out of the open fruits and carried by the wind. We have noticed that there is typically a range of variation of seed size, shape and degree of development of the unilateral (distal) wing, even within a single locule of extant Lagerstroemia (Fig. 14). The seeds of Shirleya are also variable, with small seeds found closely packed against larger ones. In both the fossil Shirleya and extant Lagerstroemia, seed shape is partly the result of tight packing within the locules, resulting in seeds curved to the left or right and more symmetrical seeds centrally (Figs. 8, 15, 20, 21). Variation in seed size and shape of this type is common in the Lythraceae, and has been documented for a number of genera in both fossil and extant examples (e.g., Decodon, Kvaek and Sakala, 1999
).
Whereas the presence of a distal wing on seeds of Shirleya and Lagerstroemia is clearly useful in wind dispersal, we suspect that it may also serve to lodge the seed into the substrate for germination. During dispersal, winged seeds like those in extant Lagerstroemia are thin, dry, and papery, and the embryo, being confined to the basal part of the seed, is the heaviest part, which presumably would effectively serve this lodging purpose. A second possible value of a parenchymatous wing of this type occurs if seeds are waterborne. When we soaked extant Lagerstroemia seeds in water, after several days the wings expanded several times their original thickness, resulting in a solid parenchymatous pad of tissue (Fig. 16). This tissue differs from the distal wings of Shirleya seeds only in being solid parenchyma instead of being bilobed with a central cavity. Permineralized fruits of Shirleya are preserved with the parenchymatous pad of tissue fully inflated (Figs. 8, 20, 21, 29). The wings are expanded like this because they most likely were saturated with mineral-charged water during the silicification process.
What is the potential function of a seed with an inflated wing containing a central cavity? Extant Lagerstromeia trees and shrubs represent one of the genera of the Lythraceae not closely tied to an aquatic plant habitat. Although Shirleya was most likely also not an aquatic plant, it was probably growing in or near the margin of a taxodiaceous swamp (Pigg and Rothwell, 2001
). The presence of a central cavity within the parenchymatous wing may have served as a means for capturing air and maintaining the seeds afloat if they landed in water. During germination in muddy, possibly anoxic substrate, the central cavity could even act as a snorkeling device, assuring the seedling of oxygen (Finley A. Bryan, Cape Fear Botanical Garden, personal communication). Plants growing in and around aquatic habitats often have specialized types of tissues for this purpose (Sculthorpe, 1967
; Rodriguez-de la Rosa et al., 1998
). Some other lythraceous seeds have a spongy interior that is thought to be an adaptation for the aquatic habitat (Sahni, 1943
). Decodon and Nesaea are true aquatic plants with largely parenchymatous seeds and have aerenchymatous vegetative tissues (Schrenk, 1889
; Sculthorpe, 1967
; Tiffney, 1981
; Little and Stockey, 2003
). Sahni (1943)
noted that the fossil fruit Enigmocarpon had seeds that resembled those of Decodon in structure, and he suggested that this tendency to retain parenchyma in the seed might be related to an original aquatic habitat for the family. Corner (1976)
interpreted the distal wing of the Lagerstroemia seed as developing by the extension of the distal end of the raphe. It is interesting that, although they are quite similar to Decodon, Sahni (1943)
described Enigmocarpon seeds as having "a swollen raphe" with the larger amount of parenchymatous tissue forming alongside it. Lythraceous genera with a circular "wing" extending around the central body might thus be considered adaptations for wind and/or water dispersal. Punica's fleshy sarcotesta, in contrast, is more likely to be animal (mammal) dispersed (Tiffney, 1984
).
The presence of Shirleya grahamae in the Yakima Canyon flora thus documents a newly recognized extinct genus of the Lythraceae in the Miocene of western North America. Although by the late Neogene, most fossil plant remains can be assigned to extant genera, or often infrageneric levels, extinct genera are also known. These include Nordenskioldia Heer and Pseudofagus Smiley & Huggins, both of which occur in the Miocene Clarkia flora of the eastern Columbia River Basin (Smiley and Rember, 1985
). Further study of the Yakima Canyon flora may document additional extinct forms from the western Columbia River Basin as well.
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FOOTNOTES |
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4 Author for correspondence: e-mail: kpigg{at}asu.edu
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Borgardt S. J. K. B. Pigg 1999 Anatomical and developmental study of petrified Quercus (Fagaceae) fruits from the middle Miocene, Yakima Canyon, Washington, USA. American Journal of Botany 86: 307-325
Cevallos-Ferriz S. R. S. R. A. Stockey 1988 Permineralized fruits and seeds from the Princeton chert (Middle Eocene) of British Columbia: Lythraceae. Canadian Journal of Botany 66: 303-312[Web of Science][Medline]
Coleman A. L. 2004 Anatomically preserved Taxodium, from the middle Miocene of Yakima Canyon, Washington. Master's thesis, Arizona State University, Tempe, Arizona, USA
Corner E. J. H. 1976 The seeds of dicotyledons, vols. 1 and 2. Cambridge University Press, Cambridge, UK
Dahlgren R. R. F. Thorne 1984 The order Myrtales: circumscription, variation, and relationships. Annals of the Missouri Botanical Garden 71: 633-699[CrossRef][Web of Science]
Dorofeev P. I. 1963 Tretichnya floryzapaduoi Sibiri. 231–234, Izdatelstvo Akademi, Nauk, SSSR. Botanicheski Institut, V. L. Komarova, Leningrad, Russia (in Russian)
Duke N. C. B. R. Jackes 1987 A systematic revision of the mangrove genus Sonneratia (Sonneratiaceae) in Australasia. Blumea 32: 277-302[Web of Science]
Friis E. M. 1985 Angiosperm fruits and seeds from the Middle Miocene of Jutland (Denmark). Det Kongelige Danske Videnskabernes Selskab. Biologiske Skrifter 24: 1-185 Munksgaard, København, Denmark
Fujiki T. A. Momohara Y. Yasuda 2001 Morphology of fossil Lagerstroemia pollen in the interglacial sediments in Japan. Japanese Journal of Historical Botany 10: 91-99 (in Japanese, English summary)
Furtado C. X. M. Srisuko 1969 A revision of Lagerstroemia L. (Lythraceae). Garden Bulletin 185–335
Gardner S. P. Sidisunthorn V. Anusarnsunthorn 2000 A field guide to forest trees of northern Thailand. Kobfai Publishing Project, Bangkok, Thailand
Graham A. S. A. Graham 1971 The geologic history of the Lythraceae. Brittonia 23: 335-346[CrossRef][Web of Science][Medline]
Graham S. 1999 The emerging picture of Lythraceae: cladistic analysis of morphological and cpDNA characters. XVI International Botanical Congress, St. Louis, Missouri, Abstracts, Abstract Number: 3581, Session 20.1.2
Graham S. A. J. V. Crisci P. C. Hoch 1993a Cladistic analysis of the Lythraceae sensu lato based on morphological characters. Botanical Journal of the Linnean Society 113: 1-33[CrossRef]
Graham S. A. K. Oginuma P. H. Raven H. Tobe 1993b Chromosome numbers in Sonneratia and Duabanga (Lythraceae s. l.) and their systematic significance. Taxon 42: 35-41
Graham S. A. H. Tobe P. Baas 1986 Koehneria, a new genus of Lythraceae from Madagascar. Annals of the Missouri Botanical Garden 73: 788-809[CrossRef][Web of Science]
Huang Y. S. Shi 2002 Phylogenetics of Lythraceae sensu lato: a preliminary analysis based on chloroplast rbcL gene, psa-A-ycf3 spacer, and nuclear rDNA internal transcribed spacer (ITS) sequences. International Journal of Plant Sciences 163: 215-225[CrossRef]
Johnson L. A. S. B. G. Briggs 1984 Myrtales and Myrtaceae—a phylogenetic analysis. Annals of the Missouri Botanical Garden 71: 700-756[CrossRef][Web of Science]
Joshi A. C. J. Venkateswarlu 1936 Embryological studies in the Lythraceae. III. Proceedings of the Indian Academy of Sciences. Section B 3: 337-400
Judd W. S. C. S. Campbell E. A. Kellogg P. F. Stevens M. J. Donoghue 2002 Plant systematics: a phylogenetic approach, 2nd ed. Sinauer, Sunderland, Massachusetts, USA
Koehne E. 1881–1886 Lythraceae monographice describuntur. Engler's Botanische Jahrbücher, 1881–1886, 1–7
Koehne E. 1885 The Lythraceae of the United States. Botanical Gazette 10: 269-277[CrossRef]
Koehne E. 1903 Lythraceae. In A. Engler [ed.], Das Pflanzenreich IV. 216. Heft 17. Engelmann, Leipzig, Germany
Kvaek Z. J. Sakala 1999 Twig with attached leaves, fruits and seeds of Decodon (Lythraceae) from the Lower Miocene of northern Bohemia, and implications for the identification of detached leaves and seeds. Review of Palaeobotany and Palynology 107: 201-222
Little S. A. R. A. Stockey 2002 Fossil Duabanga-like leaves (Lythraceae) from the Princeton chert. Botany 2002, Botanical Society of America Annual Conference, Madison Wisconsin Abstract no. 345. http: //www.2002.botanyconference.org/#abstracts
Little S. A. R. A. Stockey 2003 Vegetative growth of Decodon allenbyensis (Lythraceae) from the middle Eocene Princeton chert with anatomical comparisons to Decodon verticillatus. International Journal of Plant Sciences 164: 453-469[CrossRef]
Mädler K. 1939 Die Pliozane flora von Frankfurt am Main. Abhandlung Senckenbergen naturforschungs Gesellschaft 446: 1-202
Mahabale T. S. J. V. Deshpande 1957 The genus Sonneratia and its fossil allies. Palaeobotanist 6: 51-64
Mai D. H. 2001 Die mittelmiozänen und obermiozänen Floren aus der Meuroer und Raunoer Folge in der Lauitz. Teil II. Dicots. Palaeontographica 257B: 35-174
Mai D. H. H. Walter 1985 Die obereozänen Floren des NW-Sachsen und des Bitterfelder Raumes. Abhandlungen des Staatlichen Museums für Mineralogie und Geologie zu Dresden 38: 1-230
Manchester S. R. 1994 Fruits and seeds of the Middle Eocene Nut Beds Flora, Clarno Formation, Oregon. Palaeontographica Americana 58: 1-205
Manchester S. R. 1999 Biogeographical relationships of North American Tertiary floras. Annals of the Missouri Botanical Garden 86: 472-522[CrossRef][Web of Science]
Mathewes R. W. 2003 An Early Eocene flora from Quilchena, British Columbia and its paleoenvironmental significance. [abstract no. 736]: Joint Annual Meeting of the Geological Association of Canada/Mineralogical Association of Canada/Society Economic Geologists, Vancouver, British Columbia, 25–28 May 2003 Vancouver, British Columbia: GAC-MAC-SEG 28 Abstract 533. CD-ROM
Matsumoto M. A. Momohara T. A. Ohsawa Y. Shoya 1997 Permineralized Decodon (Lythraceae) seeds from the Middle Miocene of Hokkaido, Japan with reference to the biogeographic history of the genus. Japanese Journal of Historical Botany 5: 53-65
Miki S. 1936 Plant fossils from Stegodon and Elephas beds near Akashi, Japan. Chikyu (the Globe) 26: 155-160
Miki S. 1937 Plant fossils form the Stegodon Beds and the Elephas Beds near Akashi. Japanese Journal of Botany 8: 303-341
Miyoshi N. T. Fujiki Y. Morita 1999 Palynology of a 250-m core from Lake Biwa: a 430,000-year record of glacial-interglacial vegetation change in Japan. Review of Palaeobotany and Palynology 104: 267-283[CrossRef][Web of Science]
Muller J. 1981 Fossil pollen records of extant angiosperms. Botanical Review 47: 1-142
Pigg K. B. S. M. Ickert-Bond J. Wen 2004 Anatomically preserved Liquidambar (Altingiaceae) from the middle Miocene of Yakima Canyon, Washington state, USA, and its biogeographic implications. American Journal of Botany 91: 499-509
Pigg K. B. G. W. Rothwell 2001 Anatomically preserved Woodwardia virginica (Blechnaceae) and a new filicalean fern from the middle Miocene Yakima Canyon flora of central Washington, USA. American Journal of Botany 88: 777-787
Prakash U. 1965 Fossil wood of Lagerstroemia from the Tertiary of Burma. Current Science 34: 484-485
Prakash U. 1971 [issued 1973] Fossil woods from the Tertiary of Burma. Palaeobotanist 20: 48-70
Rode K. P. 1933 A note on fossil angiospermous fruits from the Deccan Intertrappean beds of the Central Provinces. Current Science 2: 171-172
Rodriguez-de la Rosa R. A. S. R. S. Cevallos-Ferriz A. Silva-Pineda 1998 Paleobiological implications of Campanian coprolites. Palaeogeography, Palaeoclimatology, Palaeoecology 142: 231-254
Sahni B. 1943 Indian silicified plants. 2. Enigmocarpon parijai, a silicified fruit from the Deccan, with a review of the fossil history of the Lythraceae. Proceedings of the Indian Academy of Science, Section B 17: 59-96
Sahni B. K. P. Rode 1937 Fossil plants from the Intertrappean beds of Nohgaon Kalan in the Deccan, with a sketch of the geology of the Chindwara district. Part I. Proceedings of the National Academy of Science of India, 1937 7: 165-174
Schrenk J. 1889 On the floating tissue of Nesaea verticillata (L.) H. B. K. Bulletin of the Torrey Botanical Club 16: 315-323[CrossRef]
Sculthorpe C. D. 1967 The biology of aquatic vascular plants. Koeltz Scientific Books, Königstein, Germany
Shi S. Y. Huang F. Tan X. He D. E. Boufford 2000 Phylogenetic analysis of the Sonneratiaceae and its relationship to Lythraceae based on ITS sequences of nrDNA. Journal of Plant Research 113: 253-258[CrossRef][Web of Science]
Shukla V. B. 1958 Sahnianthus dinectrianum, sp. nov., a new species of the petrified flower Sahnianthus from the Eocene beds of the Deccan. Journal of the Palaeontological Society of India 3: 114-118
Smiley C. J. W. C. Rember 1985 Composition of the Miocene Clarkia flora. In C. J. Smiley [ed.], Late Cenozoic history of the Pacific Northwest. 95–112, Pacific Division, American Association for the Advancement of Science, San Francisco
Srivastava G. P. M. P. Bande 1990 [issued 1992] Fossil woods of Terminalia and Lagerstroemia from the Late Cenozoic beds of Mahuadanr, Palamu District, Bihar. Palaeobotanist 39: 333-337
Takhtajan A. 1996 Anatomia seminum comparativa, vol. 3, Dichotyledones. Rosidae I. Petropoli, Mir et Semja
Tanai T. K. Uemura 1991 The Oligocene Noda flora from theYuya-wan area of the western end of Honshu, Japan. Part 1. Bulletin of the National Museum, Tokyo, Series C 17: 57-80
Tcherepova M. 2001 Investigations of two anatomically preserved fruits (Rhamnaceae and Nyssaceae) from the middle Miocene Yakima Canyon flora of Washington state, USA. Masters' thesis, Arizona State University, Tempe, Arizona, USA
Tiffney B. H. 1981 Fruits and seeds of the Brandon lignite. IV. Microdiptera (Lythraceae). Journal of the Arnold Arboretum 62: 487-516[Web of Science]
Tiffney B. H. 1984 Seed size, dispersal syndromes, and the rise of the angiosperms: evidence and hypothesis. Annals of the Missouri Botanical Garden 71: 551-576
Tiffney B. H. 1994 Re-evaluation of the age of the Brandon Lignite (Vermont, USA) based on plant megafossils. Review of Palaeobotany and Palynology 82: 299-315[CrossRef]
Tolan T. L. S. P. Reidel M. H. Beeson J. L. Anderson K. R. Fecht D. A. Swanson 1989 Revisions to the estimates of the area and extant and volume of the Columbia River Basalt Group. In S. P. Reidel and P. R. Hooper [eds.], Volcanism and tectonism in the Columbia River flood-basalt province. Geological Society of America. Special Paper 239, 1–20. Geological Society of America, Boulder, Colorado, USA
Trivedi T. 1956 Fossil dicotyledonous leaf impressions from the Intertrappean Beds of Bharatwada, Nagpur District. Journal of the Palaeontological Society of India 1: 186-188
Venkateswarlu J. 1937 A contribution to the embryology of Sonneratiaceae. Proceedings of the Indian Academy of Science 5: 487-516
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