EVOLUTIONARY STUDIES OF ATRIPLEX: PHYLOGENETIC RELATIONSHIPS OF ATRIPLEX PLEIANTHA

Atriplex pleiantha Weber differs from all other species of Atriplex in having 1) multiple female flowers subtended by two bracts, 2) female flowers with a perianth, and 3) embryos with radicles pointing downwards. Because of these significant differences it is proposed that Atriplex pleiantha be elevated to the level of a separate genus and be designated Proatriplex pleiantha (Weber) Stutz & Chu. The closest relatives of Proatriplex appear to be Archiatriplex, Endolepis, Exomis, and Microgynoecium. These are all diploid, monoecious annuals, have non-Kranz type leaf anatomy, and female flowers with a perianth.     

The need to re-investigate the nature of homoplastic characters: an ontogenetic case study of the 'bracteoles' in Atripliceae (Chenopodiaceae)

Background and Aims

Within Chenopodioideae, Atripliceae have been distinguished by two bracteoles enveloping the female flowers/fruits, whereas in other tribes flowers are described as ebracteolate with persistent perianth. Molecular phylogenetic hypotheses suggest ‘bracteoles’ to be homoplastic. The origin of the bracteoles was explained by successive inflorescence reductions. Flower reduction was used to explain sex determination. Therefore, floral ontogeny was studied to evaluate the nature of the bracteoles and sex determination in Atripliceae.

Methods

Inflorescences of species of Atriplex, Chenopodium, Dysphania and Spinacia oleracea were investigated using light microscopy and scanning electron microscopy.

Key Results

The main axis of the inflorescence is indeterminate with elementary dichasia as lateral units. Flowers develop centripetally, with first the formation of a perianth primordium either from a ring primordium or from five individual tepal primordia fusing post-genitally. Subsequently, five stamen primordia originate, followed by the formation of an annular ovary primordium surrounding a central single ovule. Flowers are either initially hermaphroditic remaining bisexual and/or becoming functionally unisexual at later stages, or initially unisexual. In the studied species of Atriplex, female flowers are strictly female, except in A. hortensis. In Spinacia, female and male flowers are unisexual at all developmental stages. Female flowers of Atriplex and Spinacia are protected by two accrescent fused tepal lobes, whereas the other perianth members are absent.

Conclusions

In Atriplex and Spinacia modified structures around female flowers are not bracteoles, but two opposite accrescent tepal lobes, parts of a perianth persistent on the fruit. Flowers can achieve sexuality through many different combinations; they are initially hermaphroditic, subsequently developing into bisexual or functionally unisexual flowers, with the exception of Spinacia and strictly female flowers in Atriplex, which are unisexual from the earliest developmental stages. There may be a relationship between the formation of an annular perianth primordium and flexibility in floral sex determination.     

Mineral ion composition and osmotic relations of Atriplex confertifolia and Eurotia lanata

Summary Periodic collections of Atriplex confertifolia and Eurotia lanata leaf tissue throughout the growing season were analyzed for osmotic potential, water content, and concentration of Na⁺, K⁺, soluble Ca⁺⁺, Cl^-, and SO₄ ^-- ions. Ionic concentrations of these two species exhibited marked similarities to corresponding values for European members of the same genera. Atriplex confertifolia, like many other Atriplex species, behaves as an alkali halophyte and accumulates Na⁺, while E. lanata appears to favor accumulation of K⁺ as did its European counterpart, E. ceratoides.The analyses showed a much broader range of tissue moisture contents and osmotic potentials during the season for Atriplex than for Eurotia. The differences in leaf water relations between the two species are possibly related to the greater NaCl accumulation by Atriplex as compared to Eurotia. An apparent advantage exists for Atriplex in prolonging physiological activity and carbon gain in the dry portion of the late summer by NaCl accumulation.     

Visual discrimination between two sexually deceptive <Emphasis Type="Italic">Ophrys</Emphasis> species by a bee pollinator

Almost all species of the orchid genus Ophrys are pollinated by sexual deception. The orchids mimic the sex pheromone of receptive female insects, mainly hymenopterans, in order to attract males seeking to copulate. Most Ophrys species have achromatic flowers, but some exhibit a coloured perianth and a bright, conspicuous labellum pattern. We recently showed that the pink perianth of Ophrys heldreichii flowers increases detectability by its pollinator, males of the long-horned bee Eucera berlandi. Here we tested the hypothesis that the bright, complex labellum pattern mimics the female of the pollinator to increase attractiveness toward males. In a dual-choice test we offered E. berlandi males an O. heldreichii flower and a flower from O. dictynnae, which also exhibits a pinkish perianth but no conspicuous labellum pattern. Both flowers were housed in UV-transmitting acrylic glass boxes to exclude olfactory signals. Males significantly preferred O. heldreichii to O. dictynnae flowers. In a second experiment, we replaced the perianth of both flowers with identical artificial perianths made from pink card, so that only the labellum differed between the two flower stimuli. Males then chose between both stimuli at random, suggesting that the presence of a labellum pattern does not affect their choice. Spectral measurements revealed higher colour contrast with the background of the perianth of O. heldreichii compared to O. dictynnae, but no difference in green receptor-specific contrast or brightness. Our results show that male choice is guided by the chromatic contrast of the perianth during the initial flower approach but is not affected by the presence of a labellum pattern. Instead, we hypothesise that the labellum pattern is involved in aversive learning during post-copulatory behaviour and used by the orchid as a strategy to increase outcrossing.     

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.     

FLOWER DEVELOPMENT IN DIOECIOUS SPINACIA OLERACEA (CHENOPODIACEAE)

Spinacia oleracea (Chenopodiaceae) is a potential model system for studies of mechanisms of sex expression and environmental influences on gender in dioecious species. Development of the male and female flowers and inflorescences of spinach were studied to determine when the two sex types can be distinguished. We found that female inflorescence apices are significantly larger than those of the male. Flower primordia are similar in size prior to perianth initiation, but the male primordia develop at a faster rate. Another distinguishing feature at this early stage is the larger bract subtending the female primordium. The two flower types become readily distinguishable when the perianth initiates. Male flowers produce four sepals and four stamens in a spiral pattern in close succession. Female flowers produce two alternate perianth parts that enlarge somewhat before the gynoecium becomes visible. There are no traces of gynoecia in male flowers or of stamens in female flowers. We propose that plant sex type is determined before inflorescence development, prior to or at evocation.     

Nitrogen and Phosphorus Fertilization for some Atriplex Plants Grown on Metal-contaminated Soils

There is little information available about the impact of nitrogen and phosphorus fertilization on the uptake of metals by Atriplex plants. A series of pots experiments were conducted to define the metals uptake response of four Atriplex species to urea (U) and superphosphate (SP) fertilization. The studied Atriplex species were river saltbush (Atriplex amnicola), wavy saltbush (Atriplex undulata), quail saltbush (Atriplex lentiformis), and old man saltbush (Atriplex nummularia). The growth and metals uptake of Atriplex species were significantly (P < 0.05) affected by the fertilizer treatments. U reduced the soil pH by 10% compared to the control. SP reduced the availability of Zn, Pb, and Cd by 24, 16, and 28% compared to the control. U increased the shoots Zn and Pb by 16 and 20% compared to SP. The combined application of U+SP reduced the Zn and Pb concentrations in the shoots by 10 and 13% compared to U alone. U increased the root-to-shoot transfer of Zn and Pb by about 30 and 49%. Root phosphorus (P) and calcium (Ca) limit the translocation of metals to the Atriplex shoots and this may be by the precipitation of the metals in the roots. The study clearly showed that it is feasible to apply P fertilizer to alleviate root-to-shoot transfer of Zn and Pb. Moreover, pure N application should be avoided to minimize the occurrence of high levels of Zn and Pb in the Atriplex shoots.     

The role of ABC genes in shaping perianth phenotype in the basal angiosperm Magnolia

It is generally accepted that the genus Magnolia is characterised by an undifferentiated perianth, typically organised into three whorls of nearly identical tepals. In some species, however, we encountered interesting and significant perianth modifications. In Magnolia acuminata, M. liliiflora and M. stellata the perianth elements of the first whorl are visually different from the others. In M. stellata the additional, spirally arranged perianth elements are present above the first three whorls, which suggests that they have been formed within the domain of stamen primordia. In these three species, we analysed expression patterns of the key flower genes (AP1, AGL6, AP3, PI, AG) responsible for the identity of flower elements and correlated them with results of morphological and anatomical investigations. In all studied species the elements of the first whorl lacked the identity of petals (lack of AP3 and PI expression) but also that of leaves (presence of AGL6 expression), and this seems to prove their sepal character. The analysis of additional perianth elements of M. stellata, spirally arranged on the elongated floral axis, revealed overlapping and reduced activity of genes involved in specification of the identity of the perianth (AGL6) but also of generative parts (AG), even though no clear gradient of morphological changes could be observed. In conclusion, Magnolia genus is capable of forming, in some species, a perianth differentiated into a calyx (sepals) and corolla (petals). Spirally arranged, additional perianth elements of M. stellata, despite activity of AG falling basipetally, resemble petals.     

COMPARATIVE MORPHOLOGY OF THE CAPITULUM OF ENCELIOPSIS (ASTERACEAE: HELIANTHEAE)

Features of the capitula of all four species of Enceliopsis were examined with light and scanning electron microscopy, measured, and subjected to univariate analysis. Differences were found in the complement, distribution, and density of trichomes, the size of the receptacle, ray ligule, and disk corolla tube, and the size and shape of the phyllaries, paleae, disk corolla throats, and achenes. Morphology of trichomes, phyllaries, and achenes, as well as other vegetative characteristics, show that E. nudicaulis, E. covillei and E. argophylla form a group separate from E. nutans. Features of the achene suggest affinity of the former group with Geraea, whereas features of the trichomes and achene of E. nutans support affinity with Encelia. Characters of the receptacle, paleae, ray and disk corollas, and achene clearly show that E. nudicaulis, E. covillei, and E. argophylla are distinct.     

Effects of salinity on growth,membrane permeability and root hydraulic conductivity in three saltbush species

The species of the genus Atriplex have been introduced in West Asia and North Africa to determine their adaptability for use as fodder species. These halophytes are well adapted to extreme environmental conditions and may possess interesting properties for soil rehabilitation. The effect of NaCl stress on growth, water relation and mineral nutrition were investigated in three xero-halophyte species of Atriplex used for rehabilitation of arid steppe in Algeria. Atriplex halimus, Atriplex canescens and Atriplex nummularia, were cultivated in hydroponic conditions and treated with increasing doses of NaCl (0–300 mM). All species showed positive plant growth for low and moderate levels of salinity. A. halimus had higher dry weight production than A. nummularia and A. canescens in high salinity concentration. Increasing concentration of salinity induced decrease in chlorophyll content (Chl a and b) and root hydraulic conductivity (L₀) in all species, especially in A. canescens. All three species showed marked increase in electrolyte leakage across the salinity gradient. In addition all species were able to accumulate a large quantity of sodium (Na), chloride (Cl) and proline and to maintain higher relative water content, which was probably associated with a greater capacity for osmotic adjustment, whereas potassium (K) and calcium (Ca) decreased with increase salinity. The data suggest that salt tolerance strategies in all Atriplex species could involve a delicate balance among ion accumulation, osmotic adjustment, production of osmotica and maintenance of relative water content and growth.     

Pollen morphology and systematics of Atripliceae (Chenopodiaceae)

Pollen morphology of 58 species from 17 putative genera of the tribe Atripliceae (Chenopodiaceae) was investigated using light (LM) and scanning electron microscopy (SEM). Morphological variation was analyzed based on a dense sampling of the subtribes Atriplicinae and Eurotiinae, including many of the species in the two largest genera: Atriplex and Obione. The pantoporate pollen grains of Atripliceae are characterized by their spheroidal or subspheroidal shape, flat or moderately vaulted mesoporia with 21–120 pores, tectum with 1–8 spinules and 5–28(?38) puncta per?µm², and 1–13 ectexinous bodies bearing 1–7 spinules each. Taxonomic relevance of the most important pollen morphological characters is discussed (pollen diameter, pore number, pore diameter, interporal distance, spinule and puncta density and ratio, number of ectexinous bodies, and their spinules). Pollen morphological data support the exclusion of Suckleya from the tribe and the recognition of subtribe Eurotiinae, but suggest that it needs to be reviewed. Pollen does not support generic recognition of Atriplex, Neopreissia and Obione and infrageneric subdivisions as currently recognized, and suggests the need to review them. Smaller or monotypic genera, such as Axyris, Ceratocarpus, Endolepis, Krascheninnikovia, Microgynoecium, Proatriplex and Spinacia have distinctive pollen morphological characters that support their generic status. Grayia needs to be reevaluated; although its two species are distinct from all the other species in the study, there are notable differences between each of them, and this suggests they may not form a natural group. Multivariate techniques were employed to investigate if there are discrete patterns of variation within Atripliceae. Principal Component Analyses (PCA) weakly differentiates four groups based on variation in pore number, puncta density per?µm², and ratio between spinule and puncta density per?µm²; species of Ceratocarpus, Haloxanthium, Krascheninnikovia, Manochlamys, Microgynoecium, Spinacia, and some species of Atriplex and Obione are isolated. Preliminary results indicate that pollen data are potentially useful in the classification of the tribe, and further studies will be of taxonomic value.     

Resistance to Water Transfer in Desert Shrubs Native to Death Valley, California

Differences in plant resistance to water flow, patterns of water transport through stems, and stomatal behavior were studied on three species native to the exceptionally hot and dry habitat of Death Valley, California (—, and Larrea divaricata). Dawn xylem water potentials in July for Atriplex were — 27.5 bar under natural conditions. Corresponding values for Tidestromia and Larrea were respectively — 8.0 bar and -32.0 bar (natural) and — 7.5 bar and — 18.0 bar (irrigated). Recovery of xylem water potential in covered field plants of an irrigated transplant garden reached a maximum value in July of — 9.5 bar in Atriplex, — 5.7 bar in Tidestromia and — 7.0 bar in Larrea. Resistance to free-energy transfer was used to study resistance to water transport through the plants. Under field conditions irrigated Atriplex plants gave a whole plant resistance of 20.70 × 10⁶ s cm^-1, as compared lo 18.37 × 10⁶ s cm^-1 for Larrea and 10.01 × 10⁶ s cm^-1 for Tidestromia. Plant resistance to water How computed by this method on Atriplex plants grown under laboratory conditions gave a value of 3.73 × 10⁶ s cm^-1 at 35C. Paths of water flow in field plants as investigated with injected acid fuchsin indicated a sectorial straight type vessel. The relationship between transpiration rates and xylem water potentials in Atriplex hymenelytra was linear between transpiration 1.28 μg cm^-2 s^-1 and 2.35 μg cm^-2 s^-1 at 35°C. These results indicate that according to the Van den Honert model for water transport, plant resistance to water flow remained rather constant at this temperature. In Atriplex grown under laboratory conditions there was an adjustment of plant resistance so change in water flux at 9.5°C and 25°C. When laboratory-grown plants of Atriplex and Tidestromia were subjected to water stress by withholding water. Tidestromia closed stomata and reduced transpiration rates at higher water potentials than in Atriplex. The ratio of vapor pressure gradients of leaf/air to leaf diffusion resistance was proportional lo transpiration rates. It is suggested that Atriplex hymenelytra is a species that combines strong regulation of water loss by stomata with low efficiency of the water transport system. These plants are unable to prevent depression of plant water potential as transpiration increases. On the other hand. Tidestromia oblongifolia has little stomatal regulation of transpiration and a highly efficient water transport system. These plants sustain very high rates of transpiration without significant decrease in plant water potential.     

Ecology of SO2 resistance: III. Metabolic changes of C3 and C4 Atriplex species due to SO2 fumigations

Summary The photosynthetic processes of two ecologically-matched, herbaceous Atriplex species differed in their response to SO₂ fumigations. Atriplex triangularis, a C₃ species, was more sensitive than the C₄ species, A. sabulosa. This difference in sensitivity can be attributed in part to the higher conductance of the C₃ species in normal air and saturating light as well as greater stimulation of stomatal opening following exposure to SO₂. In addition, photosynthetic mechanisms of the C₃ species had higher intrinsic SO₂ sensitivity than the C₄ species. Differences between photosynthetic responses of these two species may also reflect differences in morphological configuration of mesophyll tissues and greater SO₂ sensitivity of the initial photosynthetic carboxlating enzyme of the C₃ species. It is likely that certain of the differences in photosynthetic SO₂ sensitivity of these contrasting C₃ and C₄ Atriplex species are characteristic of C₃ and C₄ plants in general.Abbreviations PEP carboxylase phosphoenolpyruvate carboxylase - RuBP carboxylase ribulose-1,5-bisphosphate carboxylase     

Biomass production and nitrate metabolism of Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) in cultures at different levels of nitrogen supply

Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C₃ plant) and Amaranthus retroflexus L. (C₄ plant) were maintained under open air conditions in standard soil at low and high nitrogen supply levels.A comparison of shoot dry weight and shoot length in the various series shows that the growth of the aboveground parts of both species was severely reduced under low N conditions. In both pure and mixed cultures the differences resulting from low N vs. high N conditions was less pronounced with Atriplex (C₃ plant) than with Amaranthus (C₄ plant). The root dry weight of the two species was not reduced so much under low N conditions as was the shoot dry weight. The low N plants were found to contain a larger proportion of their biomass in the roots than did the high N plants. In general the root proportion of Atriplex was greater than that of Amaranthus. The contents of organic nitrogen and nitrate and the nitrate reductase activity (NRA) per g dry weight of both species decreased continually throughout the experiments. With the exception of young plants, the low N plants always had tower contents of organic nitrogen and nitrate and nitrate reductase activities than did the high N plants. The highest values of NRA were measured in the leaf laminae. The eaves also exhibited the highest concentrations of organic nitrogen. The highest nitrate concentrations, however, were observed in the shoot axis, and in most cases the lowest nitrate values were found in the laminae. At the end of ne growing season this pattern was found to have been reversed with Atriplex, but not with Amaranthus. Thus Atriplex was able to maintain a higher NRA in the laminae than Amaranthus under low N conditions.The transpiration per leaf area of the C₄ plant Amaranthus during the course of a day was substantially lower than that of the C₃ plant Atriplex. There were no significant differences in transpiration between the low N and high N series of Amaranthus. The low N plants of Atriplex, however, clearly showed in most cases higher transpiration rates than the corresponding high N plants. These different transpiration rates of the high N and the low N Atriplex plants were also reflected in a distinct ¹³C discrimination.The sum of these results points to the conclusion that the C₃ plant Atriplex hortensis can maintain a better internal inorganic nitrogen supply than the C₄ plant Amaranthus retroflexus under low N conditions and an ample water supply, due to the larger root proportion and the more pronounced and flexible transpiration of the C₃ plant.Dedicated to Prof. Dr. Karl Mägdefrau, Deisenhofen, on the ocasion of his 80th birthday     

THE FLORAL ANATOMY OF DIPTERONIA

Hall , Benedict A. (State U. of New York, Cortland.) The floral anatcmy of Dipteronia. Amer. Jour. Bot. 48(10): 918–924. Illus. 1961.—The floral morphology of Dipteronia sinensis closely resembles that of such species of Acer as A. pseudosieboldianum. Both these species share the following characters: (1) complete flowers; (2) functional unisexuality of staminate flowers, resulting from abortion of the pistil; (3) andromonoecious condition, the same tree bearing both perfect and functionally staminate flowers; (4) nectariferous disc, extrastaminal in position. The vascular anatomy of the 2 species, described in detail in this paper, differs only in minor ways, having similar traces supplying, respectively, perianth, androecium and gynoecium. The greatest difference between the 2 genera lies in the form of the mature fruit, which in Dipteronia has the wings of the samaras completely surrounding the seeds; yet in both genera the vascular skeleton of the fruit is essentially the same. There is a similar cohesion of the vascular traces of sepals and petals in both these species. Differences between these and certain other species of Acer such as A. negundo and A. carpinifolium, herein described, greatly exceed those between A. pseudosieboldianum and Dipteronia. The flowers of A. negundo, for example, have undergone extreme reduction from the presumed ancestral type, having no petals or disc and lacking either stamens or carpels. These facts support the inclusion of Dipteronia in the Aceraceae, but make questionable its status as a genus separate from Acer.     

Responses of amino acid metabolizing enzymes from plants differing in salt tolerance to NaCl

Summary This paper reports the effects of NaCl on the in vivo activity of glutamate dehydrogenase (GDH) and glutamic-oxaloacetic transaminase (GOT) and on the in vitro activity of GDH, both enzymes having been isolated from plants differing in salt tolerance. The plants investigated were Vicia faba (salt-sensitive), Atriplex nitens and Atriplex calotheca (more or less salt-tolerant), and Atriplex halimus (halophyte) grown at various NaCl concentrations. GDH and GOT isolated from various salt-tolerant plants grown at low NaCl concentrations were inhibited in a similar way. At high NaCl concentrations, the enzyme activities remain at constant values only in the Atriplex species. GOT was more impaired by NaCl than GDH. In the case of GOT, the double reciprocal plot indicated the type of a noncompetitive inhibition. The in vitro effect of NaCl on the activity of GDH from the differentially salt-tolerant plants was of a different kind, i.e. GDH isolated from V. faba was clearly inhibited by NaCl, whereas NaCl stimulated the activity of GDH from all Atriplex species investigated. Kinetic analysis showed that substrate inhibition of GDH from A. nitens and A. calotheca grown at non-saline conditions could be removed by NaCl. Inhibition by high NaCl concentrations at low substrate concentrations was removable by increasing substrate concentrations. Moreover, the inhibition at low substrate concentrations was shown to be competitive. GDH lost this regulatory property when the plants were pretreated with 500 mM NaCl. GDH from A. halimus also possessed this control, but in contrast to A. nitens and A. calotheca, activity and control of GDH isolated from A. halimus were stimulated by pretreating the plants with 500 mM NaCl. The results showed that DDH isolated from the salt-tolerant Atriplex species was adapted to high NaCl concentrations of the tissue. Possible mechanisms of the interactions between GDH from salt-tolerant Atriplex species and NaCl are discussed.     

Biogeography and evolution of flower color in Veratrum (Melanthiaceae) through inference of a phylogeny based on multiple DNA markers

Veratrum (Melanthiaceae) comprises ca. 27 species with highly variable morphology. This study aims to construct the molecular phylogeny of this genus to infer its floral evolution and historical biogeography, which have not been examined in detail before. Maximum parsimony, maximum likelihood, and Bayesian analyses were performed on the separate and combined ITS, trnL-F, and atpB-rbcL sequences to reconstruct the phylogenetic tree of the genus. All Veratrum taxa formed a monophyletic group, within which two distinct clades were distinguished: species with white-to-green perianth formed one highly supported clade, and the species with black-purple perianth constituted another highly supported clade. Phylogenetic inference on flower color evolution suggested that white-to-green perianth was a plesiomorphic state and black-purple perianth was apomorphic for Veratrum. When species distribution areas were traced as a multi-state character, parsimonious optimization inferred that Veratrum possibly originated in East Asia. Our study confirmed previous phylogenetic and taxonomic suggestions on this genus and provided a typical example of plant radiation across the Northern Hemisphere.     

Normapolles flowers of fagalean affinity from the Late Cretaceous of Portugal

 Exquisitely preserved, charcoalified fossil flowers with in situ pollen of the Normapolles-type from the Late Cretaceous of Portugal are described and a new genus and species of Fagales, Normanthus miraensis, are established. Floral organization and structure of floral organs were studied with scanning electron microscopy and microtome sections. Flowers are actinomorphic, epigynous, and pentamerous; the perianth is simple; stamens alternate with tepals; pollen is oblate and vestibulate; the exine is thick and the tectum is scabrate-microgranulate; the gynoecium is bicarpellate and unilocular; the fruits are probably one-seeded. Comparisons with extant taxa demonstrate that N. miraensis shares many similarities with Fagales and in particular with Betulaceae. However, it is not identical with any extant taxon and cannot be included in any extant family. The combination of characters found in the fossil flowers is congruent with wind-pollination syndromes present in many extant angiosperms and clearly indicates wind-pollination of N. miraensis. Received June 13, 2000 Accepted September 28, 2000