摘要:

A new genus of fossil angiosperms (Spanomeragen. nov.) is established for flowers from two localities in the mid‐Cretaceous Potomac Group of Maryland, eastern North America. The type species,Spanomera mauldinensissp. 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 speciesStriatopollis 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 theStriatopollis paraneustype.Spanomera marylandensissp. nov., from the late Albian Patapsco Formation, is similar toS. mauldinensisbut 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 speciesStriatopollis vermimurus(Brenner) Srivastava. Carpels have pollen ofS. vermimuruson the stigma.Spanomeraprovides 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 thatSpanomerashares with other taxa suggest that the Buxaceae themselves may be closely related to Myrothamnaceae and other “lower” Hamamelididae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15743.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Specimens of cones of members of the family Williamsoniaceae, order Cycadeoidales, from Jurassic deposits of Oaxaca, Mexico, demonstrate the first bona fide evidence of the pollenbearingWeltrichiafrom the Mexican Jurassic as well as provide new information on ovulebearingWilliamsonia.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15744.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

An improved procedure is reported for determining DNA amounts of plant nuclei. Nuclei stained with propidium iodide, isolated from chopped plant leaves, were passed through an Ortho Cytofluorograph with a Lexel model 95 argon laser (514 nm) and the fluorescence measured, integrated, and recorded using an Ortho 2140 Data Acquisition computer. All nuclear samples were mixed with nuclei of Sultan barley (2C DNA content = 11.12 pg [picogram]) as an internal standard. DNA contents of ten plant species, ranging from 2C = 1.7 pg to 36.1 pg measured by flow cytometry, correlated strongly (r= 0.99, slope = + 1.00) with DNA contents determined from Feulgen‐stained nuclei of the same species using microspectrophotometry. The flow cytometric procedures were sufficiently sensitive to detect differences in DNA content between inbred lines of corn and their F1 hybrids. Our results obtained with improved procedures, specifically using propidium iodide as a fluorochrome and plant nuclei instead of chicken erythrocytes as an internal standard, demonstrate that laser flow cytometry can be a precise, rapid, and reliable method for determining nuclear DNA content of plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15745.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Because a male/female resource tradeoff is a basic assumption of many models of sex allocation in cosexual plants, statistical and manipulative methods were used to look for evidence of intersexual resource conflicts inZizania palustris. In this monoecious grass, male and female investments overlap in time within each panicle and on successive panicles, and sex allocation quickly responds to environmental changes. Nevertheless, no negative correlations were found between the numbers of florets of each sex within panicles, on consecutive panicles, or on whole plants. Removing immature fruits or florets of either sex did not significantly increase subsequent investment in the other sex. The one significant tradeoff was slightly lower total fruit production on plants with exceptionally large male investment. Wild rice, therefore, fits the tradeoff assumption of sex allocation models at the population level but rarely at the individual level.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15746.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Phylogenetic analyses of 33 species of Rubiaceae were performed using chloroplast DNA restriction site mutations. Complete cleavage maps of eight enzymes were constructed forPsychotria bacteriophilaand used as a reference in comparisons among other species. The species examined represent 33 genera from 18 tribes and four subfamilies of the Rubiaceae. A total of 268 restriction site mutations was detected, 161 of which were phylogenetically informative. Wagner and Dollo parsimony trees were compared to the classifications of Verdcourt, Bremekamp, and Robbrecht. The Wagner analysis resulted in six equally parsimonious trees with 348 steps and 54% homoplasy. Dollo analysis resulted in a single most parsimonious tree. Most clades were identical in the two analyses. The subfamily Cinchonoideae is paraphyletic. The subfamilies Antirheoideae, Ixoroideae, and Rubioideae are monophyletic, although their circumscriptions differ from previous classifications. Several new phylogenetic relationships are indicated: the tribe Chiococceae (Ixoroideae) groups withExostemaandCoutarea(Cinchonoideae); the subfamily Ixoroideae including tribe Vanguerieae is closely related toPogonopus, Pinckneya,Calycophyllum, andMussaenda(Cinchonoideae); and tribe Hamelieae forms a monophyletic group outside the subfamily Rubioideae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15747.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

The blooming period ofSaxifraga reflexaon south‐facing bluffs in interior Alaska precedes and slightly overlaps that ofSaxifraga tricuspidata. We tested the hypothesis that reproductive interference maintains this phenological separation by measuring seed set of potted 5.reflexaduring the normal and 5.tricuspidatablooming periods, with and without 5.tricuspidatanearby. During theS. reflexablooming period we placed arrays of four pots ofS. reflexain sites with and without 5.tricuspidata. Several weeks later, during theS. tricuspidatablooming period, we repeated the experiment with potted 5.reflexawhose flowering had been artificially delayed. Seed set of 5.reflexawas decreased by retarding blooming time, but not by the presence of blooming S.tricuspidata. Although both species were visited by the same pollinators, primarily syrphid flies, the presence ofS. tricuspidatadid not reduce the rate of visitation to S.reflexa. In mixed plots, visitation rates by syrphid flies were much higher to 5.reflexathan to S.tricuspidata. Interspecific floral transitions by syrphid flies were uncommon. It appears that in 1986 at this site S.reflexaexperienced no negative effects from flowering synchronously with, and occurring in close proximity to, 5.tricuspidata.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15748.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Development of the secretory cavity and formation of the subcuticular wall of glandular trichomes inCannabis sativaL. was examined by transmission electron microscopy. The secretory cavity originated at the wall‐cuticle interface in the peripheral wall of the discoid secretory cells. During the presecretory phase in development of the glandular trichome, the peripheral wall of the disc cells became laminated into a dense inner zone adjacent to the plasma membrane and a less dense outer zone subjacent to the cuticle. Loosening of wall matrix in the outer zone initiated a secretory cavity among fibrous wall materials. Membrane‐bound hyaline areas, compressed in shape, arose in the wall matrix. They appeared first in the outer and subsequently in the inner zone of the wall. The membrane of the vesicles, and associated dense particles attached to the membrane, arose from the wall matrix. Hyaline areas, often with a conspicuous electron‐dense content, were released into the secretory cavity where they formed rounded secretory vesicles. Fibrous wall material released from the surface of the disc cells became distributed throughout the secretory cavity among the numerous secretory vesicles. This wall material was incorporated into the developing subcuticular wall that increased five‐fold in thickness during enlargement of the secretory cavity. The presence of a subcuticular wall in the cavity ofCannabistrichomes, as contrasted to the absence of this wall in described trichomes of other plants, supports a polyphyletic interpretation of the evolution of the secretory cavity in glandular trichomes among angiosperms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15749.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

VacciniumsectionCyanococcuscomprises diploid, tetraploid, and hexaploid species (x = 12) all of which are highly self‐sterile. In order to assess the distribution of genetic variation within and among the diploids, population genetic analyses of allozyme data were conducted on three species:V. elliottii, V. myrtilloides, andV. tenellum. Populations were located throughout the range of these taxa in eastern North America. Data were collected at 20 loci, 12 of which are mendelian based on formal genetic analyses. Consistent with expectations for out‐crossing taxa, these species exhibited high levels of variation within populations. Eighteen loci were polymorphic with the number and frequency of alleles varying among taxa. Mean values for the number of alleles per polymorphic locus, proportion of polymorphic loci, and expected heterozygosity were 2.8, 48.2, and 0.148, respectively. High infraspecific genetic identities exceeding 0.9 indicated that these taxa are homogeneous. All populations were in Hardy‐Weinberg equilibrium with slight heterozygote excess observed inV. myrtilloidesandV. tenellum. Although total genetic diversity was lower than that observed for other predominantly out‐crossing species, it was apportioned similarly. The majority could be attributed to differences among individuals within populations. Conspecific populations were relatively undifferentiated with genetic differentiation similar to other self‐incompatible species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15750.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

Twenty‐nine recently introduced diploid (2n= 2x= 20) accessions of sectionArachisplus anA. correntina(Burk) Krap. et Greg.nom. nud. control were hybridized to the diploid A‐genome speciesA. duranensisKrap. et Greg.nom. nud. (ace. 7988), the diploid B‐genome speciesA. batizocoiKrap. et Greg. (acc. 9484), and with two subspecies of the A‐B genome (2n= 4x= 40)A. hypogaeacultivars NC 4 and Argentine. Most attempted crosses were successful and the resulting plants were vigorous. However,A. batizocoi ×accession 30008 hybrids died as seedlings andA. batizocoi ×accession 30017 produced only dwarf plants. The 710 diploid F1s fromA. batizocoiwere generally sterile, while those fromA. duranensishad fertility ranges from 5% to 84%. Meiotic chromosome relationships in diploid crosses were cytologically evaluated in 185 plants plus tester accessions. Most taxa in sectionArachishave an A genome, onlyA. batizocoiaccessions have a B genome, a D genome is represented by accessions 30091 and 30099, and two other genomic groups, represented by accessions 30011 and 30033, may be present in the section. Most cytological differentiation was found among species originally collected in southern and eastern Bolivia. On the other hand, species collected at the extremes of the distribution of sectionArachisspecies (northern Argentina to north‐central Brazil) were cytologically very similar. Evidence is presented for speciation inArachisbeing associated with both genetic differentiation and with translocated chromosomes. All taxa in the section except the D‐genome species are believed to be cross‐compatible withA. hypogaea, so germplasm introgression from mostArachisspecies should be possible.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15751.x

出版商:Wiley    

年代:1991

数据来源: WILEY

摘要:

The black maple (Acer saccharumMarsh, ssp.nigrum[Michx. f.] Desm.) gynoecium displays classical involute carpel development; carpels form, in mid‐ to late‐summer, as two separate, opposite, hood‐shaped primordia bearing naked megasporangia on inrolled carpel margins. Megasporogenesis, integument initiation, and carpel closure occur in spring; carpels fuse, forming a biloculate ovary with a short, hollow style and two divergent, dry, unicellular papillose stigmas. Transmitting tissues consist of developmentally and morphologically similar trichomes that form along the apparent carpel margins. The path from stigma to micropyle is open, but pollen tubes do not grow entirely ectotrophically. Germinating at the tip of a stigma papilla, a tube grows, apparently under the cuticle, to the papilla base. It then grows between stigma cells to the style, emerging to grow ectotrophically through the style to the compitum, where it passes into one of the locules. Within a locule, the tube grows over placenta and obturator to the micropyle, then between megasporangium cells to the female gametophyte, spreading over the surface near the egg. This study adds to our sparse understanding of gynoecium development and transmitting tissue in relation to pollen tube growth in naturally pollinated woody plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1991.tb15752.x

出版商:Wiley    

年代:1991

数据来源: WILEY