PRIMITIVE MIMOSOID FLOWERS FROM THE PALEOCENE-EOCENE AND THEIR SYSTEMATIC AND EVOLUTIONARY IMPLICATIONS

Compressed mimosoid inflorescences from a Paleocene-Eocene boundary locality in western Tennessee are the earliest fossil evidence of the subfamily. The discovery confirms the antiquity of a suite of characters that has been considered primitive based on the comparative morphology of modern mimosoids. The fossil characters are also consistent with the suggested close relationship (ancestral or sister group) between the subfamily Mimosoideae and the Dimorphandra group of the tribe Caesalpinieae (subfamily Caesalpinioideae). These flowers show little change in morphology or size in the basal to Upper Eocene interval.     

INVESTIGATIONS OF TERTIARY ANGIOSPERMS: A NEW FLORA INCLUDING EOMIMOSOIDEA PLUMOSA FROM THE OLIGOCENE OF EASTERN TEXAS

A new fossil flower and inflorescence-bearing locality has been discovered in the Oligocene of the Texas Gulf Coast. The new flora is similar to the Middle Eocene Claiborne Flora of the southeastern USA, but the quality of preservation is sometimes better in the Oligocene fossils. One component of the new flora, a mimosoid legume inflorescence, appears identical with Eomimosoidea plumosa, first reported from the Claiborne Formation of western Tennessee. Investigations of these younger specimens indicate that the taxon had changed little during the Middle Eocene-Oligocene interval, and the better quality of preservation of the Texas specimens has provided further insights into the structure of the fossils. Comparisons of the fine structural details of the pollen of Eomimosoidea with similar pollen of extant mimosoids has confirmed that the fossil genus is indeed extinct and suggests that tetrahedral tetrads of columellate, tricolporate pollen grains are ancient, possibly primitive, in the Mimosoideae.     

FOSSIL FLORAL EVIDENCE OF MALPIGHIACEAE AND AN EARLY PLANT-POLLINATOR RELATIONSHIP

Fossil flowers with affinities to Malpighiaceae have been discovered in the Middle Eocene Claiborne formation of northwestern Tennessee. The new taxon Eoglandulosa warmanensis gen. et sp. nov. Taylor and Crepet, has paired glands on the five sepals, clawed petals and tricolporate pollen with reticulate ornamentation and an unusual infratectal wall structure of anastomosing elements. The fossil is similar in wall structure to some extant species of Malpighiaceae. Glandular floral morphology in extant species is associated with specific anthophorid bee pollinators and the fossil evidence suggests that such specific plant-pollinator relationships existed during the Eocene. This fossil species also suggests that by the Eocene, South American floral elements had migrated to North America via island pathways, and that the Mississippi embayment was nearly frost-free.     

EUPHORBIOID INFLORESCENCES FROM THE MIDDLE EOCENE CLAIBORNE FORMATION

Inflorescences from the Claiborne Formation of western Tennessee are remarkably similar to those of the tribe Hippomaneae, subfamily Euphorbioideae, of the Euphorbiaceae. The fossil inflorescences are spikes of bract-subtended cymules of at least three florets each. Florets are composed of at least three stamens. Palynological features of the fossils are also shared by the Hippomaneae. Fossil pollen is tricolporate, prolate (26.9 × 20.6 μm; P/E = 1.3), with lalongate pores. Exine structure is tectate columellate with a perforate tectum. The exine is reticulate and the muri are conspicuously striate. These specimens represent the first fossil floral evidence of the Euphorbiaceae. It is surprising that inflorescences of the Hippomaneae so modern in aspect existed in the Middle Eocene, since the tribe is universally considered to be one of the most advanced in the family.     

EOCENE FLORAL EVIDENCE OF LAURACEAE: CORROBORATION OF THE NORTH AMERICAN MEGAFOSSIL RECORD

Numerous megafossils of Lauraceae have been reported from the early Tertiary of North America, but the subfamilial affinities are usually not well understood due to the great morphological variability found in extant taxa. The flowers of Androglandula tennessensis gen. et sp. nov. Taylor, from the Middle Eocene Claiborne Formation, are six-parted, pedicellate, bracteate, and have stamens with paired basal staminal glands. The flowers have ethereal oil cells and paracytic stomates throughout. The fossil species has affinities with the subtribe Cinnamomineae, and this supports suggestions that the Middle Eocene climate of the southeastern U.S. was subtropical. The existence of this fossil, and reports of the subtribe from the Eocene of Europe, indicate a South American-North American-European-southeast Asian paleodistribution suggesting that extinction in North America and Europe was the cause of the tribe's current disjunct distribution.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF NORTH AMERICA: A CATKIN WITH JUGLANDACEOUS AFFINITIES

Three specimens of one type of fossil catkin from the Middle Eocene of Tennessee are excellently preserved and have been investigated morphologically. The flowers on these catkins are subtended by elongate, three-lobed bracts, are exclusively staminate, and have three conspicuous, obovate, perianth parts that bear large peltate scales. The stamens are well preserved and contain triporate pollen grains that are equivalent to the dispersed pollen genus Momipites. Floral morphology, cuticular features, and pollen indicate close affinities with the extant genera Engelhardia, Oreomunnea, and Alfaroa of the Juglandaceae; but because the fossil catkins are distinct and are a dispersed plant organ, they are placed in a new form genus: Eokachyra. These fossil flowers represent a rare opportunity to correlate the micro- and macrofossil record and to compare the relative rates of evolution of these features. The fossil catkins also demonstrate that much structural information may be gained from the study of fossil angiosperm flowers. The similarities between the staminate flowers of the fossil catkins and the staminate flowers of Engelhardia, Oreomunnea, and Alfaroa confirm the idea that this complex has had a long evolutionary history and suggest that the pollination system of certain extant genera was well developed during Middle Eocene times.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE MIDDLE EOCENE OF NORTH AMERICA: FLOWERS OF THE CELTIDOIDEAE

Flowers from the Middle Eocene Claiborne Formation of western Tennessee have both floral and palynological features suggestive of affinities with the subfamily Celtidoideae of the Ul-maceae. Floral size, pollen size, and exine structure suggest that these flowers are intermediate between insect-pollinated ancestors and the modern wind-pollinated Celtidoideae. Thus, they represent the first direct fossil evidence supporting the widespread notion that at least some of the Amentiferae have been derived from insect-pollinated ancestors.     

A PERMINERALIZED FLOWER FROM THE MIDDLE EOCENE OF BRITISH COLUMBIA

A permineralized flower bud, two stamen clusters and one isolated stamen of similar morphology have been found in the black cherts of the Middle Eocene Allenby Formation of Princeton, British Columbia. Specimens were studied using a modified cellulose acetate peel technique and hydrofluoric acid. The single flower specimen, 4.5 mm long and 4.0 mm in diameter, represents half of a relatively mature bud of a bisexual flower with a superior ovary. The two-loculate pistil is 2.5 mm long with a solid style and a lobed stigmatic surface. No ovules have been observed in attachment. Twenty-two to 24 stamens are borne in three whorls or a tight helix. Pollen sacs of the anther are elongate with a thin connective while filaments are laminar. Anther walls contain rectangular cells with dark contents that also can be identified in isolated stamens or stamen clusters. Abundant stephanocolpate (pentacolpate), psilate pollen grains 20 μm in diameter have been isolated and examined using scanning and transmission electron microscopy. Grains are tectate, columellate with a broad foot layer that thins near the apertures, and an endexine of small platelets. The remains of four petals are surrounded by one large sepal, suggesting two in the whole flower. Morphological features of this flower are comparable to taxa of the Flacourtiaceae and Papaveraceae, but show closest similarities to the Eschscholziaeae of the Papaveraceae. Difficulties with reconciling the placement of this flower in the Eschscholziaeae and the known environment of deposition of the Princeton chert are discussed. The fossil material represents a new angiospermous taxon: Princetonia allenbyensis Stockey gen. et sp. nov., family Incertae sedis.     

THE POLLINATION BIOLOGY OF TUCKAHOE,PELTANDRA VIRGINICA (ARACEAE)

This study describes the specialized brood-site-based pollination system of Peltandra virginica Kunth (Araceae) with the chloropid fly Elachiptera formosa Loew and provides experimental evidence that gender-related changes in floral odor composition synchronize pollinator behavior with the blooming sequence. P. virginica is protogynous and does not self-pollinate because of a strong temporal separation in sexual function, and it is dependent upon insects for pollination because the spathe completely surrounds the spadix during the pistillate stage. Field observations conducted in central New Jersey and southeastern Pennsylvania showed that E. formosa is closely associated with P. virginica inflorescences. Within the floral chamber, E. formosa adults feed on pollen, mate, and find oviposition sites while the larvae complete their development. Although drosophilid and syrphid flies were collected and reared from inflorescences of both sexual stages, only E. formosa emerged from pistillate-stage inflorescences and adult E. formosa rapidly transferred fluorescent dye particles between inflorescences of both sexual stages in laboratory enclosures. These findings indicate that this fly species is the primary pollinator at our study locations. Field censuses demonstrated that although E. formosa visited P. virginica inflorescences of both sexual stages with equal frequency, the female flies preferentially oviposited within pistillate-stage inflorescences. Analysis of floral volatiles with gas chromatography-mass spectrometry showed that only the spathes emit the floral fragrance and that the composition of the floral volatiles changed during the transition from pistillate to staminate stage. A particularly noticeable change occurred in the emission ratio of the two primary floral odor components, 4,5,7-trimethyl-6,8-dioxabicyclo[3.2.1.]octane and an unidentified chemical analog with molecular weight of 142. The relationship between floral volatile composition and fly oviposition behavior was evaluated using sham inflorescences placed in the P. virginica study population. The sham inflorescences were constructed by covering spadices dissected from mature inflorescence buds with spathes excised from different-age inflorescences. After a 2-hr-long exposure period, sham inflorescences fitted with pistillate-stage spathes contained more E. formosa eggs than the sham inflorescences with staminate-stage spathes. However, the highest number of ovipositions occurred in sham inflorescences fitted with spathes excised from mature inflorescence buds. The fragrance emitted by these spathes was composed almost entirely of the two principal odor components. The decline in ovipositions observed in both real and sham inflorescences corresponded to an increase in the emission ratio of 4,5,7-trimethyl-6,8-dioxabicyclo[3.2.1.]octane to the molecular weight 142 analog. This suggests that gravid flies searching for oviposition sites used the ratio of the two primary floral volatile components as an inflorescence gender or age recognition cue.     

The mangrove palm Nypa in the geologic past of the New World

The paleontological history of Nypa, known today as the mangrovepalm, is traced through geological time back to the Late Cretaceous. Emphasis is laid on the New World occurrences, especially in NorthAmerica, where Nypa is known from fossil fruits and pollen. In SouthAmerica, the stratigraphic range of this palm extends from theMaastrichtian to the late Eocene, whereas in North America, Nypa isrestricted to only the Eocene. Nypa occurs as pollen all along theAmerican Gulf Coast from the early Eocene (Ypresian) to the late Eocene(Priabonian), while fruit records come from the early and middle Eoceneof Maryland and Texas, respectively. The floristics of these Eocenemangroves, including possible mangrove associates, and the developmentof mangrove vegetation in the neotropics through the Tertiary andQuaternary, are discussed. New paleobotanical evidence from a middleEocene faunal and floral assemblage in Texas, the Casa Blanca flora (LaredoFormation, Claiborne Group), which contains fossil Nypa pollen andfruits, is described in detail.     

Paleobotanical remains from the Paleocene–lower Eocene Vagadkhol Formation, western India and their paleoclimatic and phytogeographic implications

A small assemblage of macro- and micro floral remains comprising fossil leaf impressions, silicified wood, spores, and pollen grains is reported from the Paleocene–lower Eocene Vagadkhol Formation (=Olpad Formation) exposed around Vagadkhol village in the Bharuch District of Gujarat, western India. The fossil leaves are represented by five genera and six species, namely, Polyalthia palaeosimiarum (Annonaceae), Acronychia siwalica (Rutaceae), Terminalia palaeocatapa and T. panandhroensis (Combretaceae), Lagerstroemia patelii (Lythraceae), and a new species, Gardenia vagadkholia (Rubiaceae). The lone fossil wood has been attributed to a new species, Schleicheroxylon bharuchense (Sapindaceae). The palynological assemblage, consisting of pollen grains and spores, comprises eleven taxa with more or less equal representation of pteridophytes, gymnosperms, and angiosperms. Angiospermous pollen grains include a new species Palmidites magnus. Spores are mostly pteridophytic but some fungal spores were also recovered. All the fossil species have been identified in the extant genera. The present day distribution of modern taxa comparable to the fossil assemblage recorded from the Vagadkhol area mostly indicate terrestrial lowland environment. Low frequency of pollen of two highland temperate taxa (Pinaceae) in the assemblage suggests that they may have been transported from a distant source. The wood and leaf taxa in the fossil assemblage are suggestive of tropical moist or wet forest with some deciduousness during the Paleocene–early Eocene. The presence of many fungal taxa further suggests the prevalence of enough humidity at the time of sedimentation.     

ANATOMY AND DEVELOPMENT OF THE FLOWER AND FRUIT OF PERESKIA PITITACHE

Boke, Norman H. (U. Oklahoma, Norman.) Anatomy and development of the flower and fruit of Pereskia pititache. Amer. Jour. Bot. 50 (8): 843–858. Illus. 1963.—Flowers of P. pititache are about 6 cm in diameter and perigynous. The receptacle bears numerous broad bracts; the inner perianth segments are orange and deeply cleft; the numerous stamens develop centrifugally. The fundamentally superior gynoecium is broad and flat and consists of 10–18 connate carpels, the fertile portions of which are involute and adnate to the conical floral axis. The 8–16 ovules in each of the pocket-like locules are borne in 2 rows along the zone of adnation; placentation is axile. The short style and the style branches are lined with stigmatic tissue, which extends downward among the ovules. There is no definite stigma. The tip of the floral axis retains its meristematic characteristics beyond anthesis. In early fruit development, the rim of the floral cup grows in height, while the residual floral axis becomes a conspicuous peg-like columella. Concomitantly, the formation of numerous mucilage cells and cavities causes the ovary partitions and parts of the ovary roof to disintegrate. As a result, the seeds are contained in a single, moat-like cavity, which appears inferior. Late fruit development is characterized by the differentiation of numerous fiber sclereids in association with the extensive and complex vascular system.     

Appendix: a novel type of homeotic mutation affecting floral morphology

A mutant with altered floral morphology, designated Appendix, was observed among the progeny of a regenerated transgenic tobacco (Nicotiana tabacum) plant. Appendix flowers had small outgrowths resembling pistils on the tips of fertile anthers. No Obvious morphological changes could be seen in any other part of the plant. A more careful analysis using histological methods and scanning electron microscopy revealed that the outgrowths were composed only of a style and a stigma and that these added organs can support pollen germination and pollen tube growth. Examination of anther ontogeny using scanning electron microscopy indicated that the anther style and stigma of the Appendix mutant developed from a small group of cells at the anther tip coincident with development of the carpel style and stigma. Genetic analysis indicated that this mutation is nuclear, recessive and linked to the ‘transferred DNA’ (T-DNA) inserted during the generation of transgenic plants using Agrobacterium tumefaciens. The Appendix phenotype does not correspond to any of the other types of floral homeotic mutations that have been described so far.     

ANGIOSPERM FLOWERS AND TRICOLPATE POLLEN OF BUXACEOUS AFFINITY FROM THE POTOMAC GROUP (MID-CRETACEOUS) OF EASTERN NORTH AMERICA

A new genus of fossil angiosperms (Spanomera gen. nov.) is established for flowers from two localities in the mid-Cretaceous Potomac Group of Maryland, eastern North America. The type species, Spanomera mauldinensis sp. nov., from the early Cenomanian Elk Neck beds, has inflorescence units with terminal pistillate, and lateral staminate flowers. The organization of inflorescences and flowers is opposite and decussate. Staminate flowers typically have five tepals: two lateral, one posterior, and two in the anterior position. Each tepal is opposed to a stamen with a short filament, dorsifixed anther, and two pairs of pollen sacs. Stamens contain pollen comparable to the dispersed pollen species Striatopollis paraneus (Norris) Singh. Pistillate flowers have two lateral tepals and two anterior-posterior tepals that are opposed to two carpels. Carpels are slightly fused basally along their ventral margins and are semicircular in outline with a long, decurrent, papillate ventral stigma. Frequently this stigmatic surface has abundant attached pollen of the Striatopollis paraneus type. Spanomera marylandensis sp. nov., from the late Albian Patapsco Formation, is similar to S. mauldinensis but is known only from isolated flowers and floral parts. Staminate flowers have four stamens with dorsifixed anthers and each is opposed to a tepal. Stamens contain pollen comparable to the dispersed pollen species Striatopollis vermimurus (Brenner) Srivastava. Carpels have pollen of S. vermimurus on the stigma. Spanomera provides further evidence of unisexual but probably insect-pollinated flowers among mid-Cretaceous, early nonmagnoliid (“higher”) dicotyledons, and is interpreted as closely related to extant Buxaceae. Characters that Spanomera shares with other taxa suggest that the Buxaceae themselves may be closely related to Myrothamnaceae and other “lower” Hamamelididae.     

CAESALPINIA SUBGENUS MEZONEURON (LEGUMINOSAE,CAESALPINIOIDEAE) FROM THE TERTIARY OF NORTH AMERICA

Legume fruits from the Eocene of Tennessee and Wyoming and the Miocene of Idaho are described and assigned to Caesalpinia subgenus Mezoneuron (Caesalpinioideae), an extant Paleotropical taxon that does not occur in North or South America today. Morphological and anatomical details of the fruits are used in evaluating their systematic relationships. The features of the fossil fruits are accommodated only within this extant subgenus. These fossils represent the only reliable known occurrence of C. subgenus Mezoneuron in the paleobotanical record. These fossils suggest that subgenus Mezoneuron was distinct from subgenus Caesalpinia by the Middle Eocene. Further, they document the widespread occurrence of this currently Paleotropical group for at least 30 million years in North America.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF NORTH AMERICA: STIPULATE LEAVES OF THE RUBIACEAE INCLUDING A PROBABLE POLYPLOID POPULATION

A comparative study was made of the gross morphology, fine venation and cuticular features of Leitneria fioridana Chapman, the single living representative of the order Leitneriales and Leitneria eocenica (Berry) Brown, presumbaly a related fossil species. In addition to the type material, newly collected fossil specimens were investigated from clay pits in the Middle Eocene, Claiborne Formation, of western Tennessee and Kentucky. Foliate stipules attached to the petioles of several specimens suggest the assignment of this fossil leaf type to the genus Leitneria is incorrect. The nature of the gross morphology, fine venation and cuticular features confirms the misidentification. Previously, various specimens of this fossil leaf type have been placed in eight species of seven genera in seven families of six angiosperm orders, none of which are correct systematically. The gross morphology, venation and cuticular characters of the fossil leaf are distributed among a few extant South American genera of arborescent Rubiaceae. The fossil is an extinct rubiaceous leaf type which cannot be placed within a single modern subfamily, tribe or genus of the family. The organ genus, Paleorubiaceophyllum is proposed for these leaves. Three varieties of a single fossil species, P. eocenicum, are recognized. One variety with epidermal cells nearly twice the size of the others may represent a polyploid population.