摘要:

Cladistic analysis ofPoachloroplast DNA (cpDNA) restriction sites tested previously hypothesized relationships within the genus. Forty‐six taxa representing 19 sections or groups and three subgenera ofPoaand two out‐group genera,PuccinelliaandBellardiochloa, are analyzed. Five major and several minor cpDNA groups are identified. The cpDNA cladogram is generally congruent with the subgeneric taxonomy ofPoa. Exceptions are reclassified or are discussed in terms of character incompatibilities and possible reticulation events. The cpDNA tree detected relationships among sections that were unresolved using traditional character sets and provides a basis for polarization of morphological character states. An assessment of biogeographic events based on the cpDNA tree suggests: 1)Poaoriginated in Eurasia; 2) at least six groups of species independently colonized North America; and 3) two of the latter groups colonized South America, and one closely related group colonized New Zealand and Australia. The cpDNA tree provided a conservative estimate of the number of amphi‐neotropical disjunctions when compared to the known number of species disjunctions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12549.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The organization of isolated embryo sacs and eggs ofPlumbago zeylanicawas described before and after fertilization using microscopic cytochemistry and scanning electron microscopy. Major developmental events of fertilization, including preferential fertilization and early embryogenesis, are described in isolated embryo sacs. The two sperms, one unassociated with vegetative nucleus (Sua) and the other physically associated with the vegetative nucleus (Svn), fuse with nuclei of egg and central cell, respectively. The zygote divides asymmetrically to form a two‐celled embryo, consisting of a massive suspensor occupying most of the micropylar portion of the embryo during early embryogenesis. Plastids are distributed in the perinuclear and micropylar regions of the egg cell and in cytoplasmic strands of the central cell before fertilization. Calcofluor white‐positive fibrillar material in the filiform apparatus (presumedβ‐1,4 linked glucans) was investigated using scanning electron microscopy. The egg ofP. zeylanicacan easily be divided into three cytologically distinct regions: 1) perinuclear cytoplasm, 2) lateral cytoplasm, and 3) micropylar cytoplasm. Cytological differences are evident in the organization of the cell walls, general degree of vacuolization, and the distribution of heritable organelles, storage bodies, and microtubules. The present study supports the concept that the egg ofP. zeylanicaplays combined synergid and gamete functions.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12550.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

For bothEpilobium angustifoliumandAnaphalis margaritacea, the two dominant species in primary succession on the Pumice Plains on Mount St. Helens, density of the seed rain far exceeds the density of colonists. To test the hypothesis that colonization rate is limited by processes occurring during seedling establishment, we investigated the effects of subsurface moisture (using a wet and a dry site), microtopography (fine and coarse pumice particles), and seed size (five size classes), and monitored the fates of seedlings originating from experimentally sown seed for 2 years. Subsurface moisture had the strongest effect on seedling emergence and survival. By the second year there were over 20 times as many seedlings in the wet site as in the dry site; survival in the latter site was nearly zero. Coarse pumice plots had greater establishment than did fine pumice plots. Emergence rate increased significantly with increasing seed size, but this initial difference disappeared by the second year.A. margaritaceaestablished under a wider range of conditions than didE. angustifolium. We conclude that colonization by these species, and hence rate of primary succession, is limited by availability of safe sites for germination and establishment and not by seed dispersal. Safe sites are defined primarily by the level of subsurface moisture and secondarily by microtopography and seed size, and have a greater effect on seedling emergence than on seedling survival.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12551.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Previous work has suggested that the floras of the separate regions of the high Andes are the products of disparate geographical, ecological, and geological factors. Among the important factors that differ among the regions are distances from source areas of propagules, climates, and differential effects of Pleistocene glaciations. To ascertain the relative importances of these factors in shaping the modern floras, and to test hypotheses about the causes of observed generic diversity patterns, models of abundances of species per genus were tested against data from three samples representing the major vegetation zones of the high Andes (páramo, puna, and austral alpine). While originally proposed for intraspecific phenomena, abundance models (broken stick, log normal, geometric series, and log series) appear to be applicable to supraspecific taxa and were used to assess alternative hypotheses. Potential sources of genera now present in the sample areas were compared, and coefficients of similarity were computed between these samples and between each of them and two North American high‐elevation floras. Propagule types in the three Andean samples were also scored to see if methods of fruit dispersal differed. Results showed that all areas fit the geometric series model if abundance plots of ranked genera were compared, but these results were heavily influenced by the large number of genera represented by only one species. Both the puna and austral alpine samples fit the log series models, indicating that the habitats of these areas are relatively uniform and that arrival of propagules was random over time. The lack of a fit of the Colombian data to the log series or log normal models is due primarily to a large number of species‐rich genera relative to other areas. These findings support the hypothesis that there has been a pronounced level of autochthonous speciation in the Colombian Andes relative to other areas. Coefficients of similarity at the generic level show that a given flora is most similar to that of the nearest sample area within the same continent. However, the floristic similarity between Tierra del Fuego and the high mountains of Colorado is as high as that between the Tierra del Fuego sample and the neighboring Argentina sample, indicating that similarities in climate can be as important as distance in determining the composition of some Andean floras.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12552.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The species‐area relationship and its underlying explanatory mechanisms were investigated in a primary successional sere on a southeastern (United States) granite outcrop. There, plant communities occupy soil‐filled depressions separated from one another by areas of bare rock. They have been termed “island communities.” Soil depth and area increase as succession proceeds fromSedum smallii, to lichen‐annual, to annual‐perennial, and to herb‐shrub‐tree stages. Although plant species richness is significantly and positively correlated with island area in the system studied (all successional stages considered), the relationship between species richness and island maximum soil depth is stronger. However, island maximum soil depth and area are significantly and positively correlated. The exponential function describes the speciesarea relationship better than the transformed power function. Within successional stage, species richness shows no significant relationship with area or depth, except for late‐successional island communities. Processes related to community successional development may explain the species‐area relationship that exists when islands of all stages are considered. However, mechanisms related to equilibrium between extinction and immigration may be responsible for the speciesarea relationship for late‐successional island communities.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12553.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Allozyme variation was investigated in 17 Japanese populations ofCampanula punctata, ten from the Izu Islands and seven in the mainland (Honshu). The data indicate that there are two groups, a mainland group and an island one, and that the systematically problematic Oshima Island (northernmost Izu island) populations are closely related to those of the other islands. Nei's genetic identity values among islands and among mainland populations were 0.95 and 0.97, respectively, while the value between island and mainland populations was 0.84, suggesting that the island populations are an independent species. Total genetic variation was nearly the same among island and mainland populations. However, the apportionment of variation within and among populations was considerably different; 14% of gene diversity exists among mainland populations, while 31% of the diversity exists among island populations. Mean outcrossing rates of self‐incompatible mainland and Oshima populations are 0.62–0.79, supporting xenogamy; those in self‐compatible island populations are 0.37–0.57 in the northern islands, indicating a mixed mating system, and 0.16–0.25 in southern ones, indicating dominant inbreeding. Total genetic diversity in each island population decreased with distance from the mainland. Genetic and geological data suggest that the ancestors of insular populations were founded on northern islands in a relatively ancient period and that they dispersed progressively to the southern ones. Chromosome number (2n= 34) and isozyme numbers indicate gene duplications in this species, which suggests it is an ancient polyploid.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12554.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

After more than 5 years of study on natural populations ofThymelaea hirsuta(L.) Endl. (Thymelaeaceae), four distinct sexual phenotypes are shown to occur: protogynous, protandrous, subandroecious (male), and subgynoecious (female) individuals. The four populations studied differ significantly in the relative abundance of sexual types. Plant size and sexual phenotype are independent in three populations. Each sexual form produces viable seeds. Growth and morphogenesis of the aerial vegetative and sexual parts are described and found not to be related to sexual phenotype. The system, called sexual tetramorphism, combines characteristics of subdioecy (subandroecious and subgynoecious individuals) and heterodichogamy (protogynous and protandrous individuals). High fruit production in females and protandrous plants vs. low fruit production in males and protogynous plants provides evidence of a strong tendency toward functional dimorphism. The probable specialization of protogynous types toward the male function and the obvious specialization of protandrous types toward the female function suggest an evolution from heterodichogamy to dioecy, sexual tetramorphism being the intermediate stage. Tetramorphism inT. hirsutaprovides further support for the hypothesis of an evolutionary pathway from heterodichogamy to dioecy.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12555.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

Anatomical investigation of the spikelet base inEriochloareveals a nonvascularized cup‐shaped structure composed of large parenchyma cells surrounding a column of tissue that is continuous with the pedicel. The cup and column are fused only at the base of the cup. No vestigial stelar node occurs in either the cup or the column. The stele branches above the cup at the rachillar node of the second glume. Therefore, the cup‐shaped callus characteristic ofEriochloaappears to be formed entirely of parenchymatous tissue and is not derived from the first glume as previously interpreted. The bead of callus at the base of the spikelet in some species ofBrachiariaalso comprises an unbranched stele surrounded by parenchyma. The vascular tissue branches and enters the first glume at the apex of the bead. The spikelet base ofUrochloahas a distinct first glume, nodal complex, and no callus parenchyma. Thus, the cup‐shaped callus ofEriochloaand the callus bead ofBrachiariaappear to be structurally similar.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12556.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The responses of seedling root systems of three species of oaks in California to two experimental soil moisture regimes were studied by comparing lateral root development, root and shoot weights, and root: shoot ratios. In the first soil moisture treatment the taproot was allowed to extend into moist soil throughout the duration of the experiment (control), while in the second treatment (shallow) the taproot grew into a dry substrate below 30 cm of moist soil. The treatments were intended to approximate soil moisture conditions experienced by oak seedlings in the field when deep soil water sources vary in their accessibility (control: accessible, shallow: inaccessible). Lateral root growth ofQuercus agrifoliadid not increase significantly when the primary root tip died in the shallow treatment, resulting in an overall decrease in the percent of the root system composed of lateral roots.Q. douglasiiandQ. lobataincreased lateral root weights by 80% and 70%, respectively, on the upper 30 cm of the primary root when the primary root tip died.Q. lobatawas the only species that decreased in shoot and root weight (25% and 21%, respectively) with the loss of the root tip, indicating that, unlike the other species, it was dependent on the primary root for maximum growth. The morphological responses of these species correspond with their distributions and also may be a factor that influences their interactions with other species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12557.x

出版商:Wiley    

年代:1990

数据来源: WILEY

摘要:

The details of shoot organization, including number of leaves per shoot, position of foliage leaves and cataphylls, position of the lateral continuation shoot, nature of axillary buds and phyllotaxis, and the pattern of shoot extension were observed and compared in five species ofTyphonium, Dracunculus vulgaris, Sauromatum venosum, Arum italicum, andHelicodiceros muscivorus, resulting in the recognition of four types of stems. Three of the four types were found in the genusTyphonium. One type was found inTyphonium giganteumandSauromatum venosumand is presumably the same inBiarum. Another type, found inT. trilobatum, T. blumei, andT. flagelliforme, is distinct in the position of the lateral continuation shoot, which arises from the axil of the n‐1 leaf and is adnate to the axis to above the n leaf. Based on the results, two groups, one of which is further subdivided into two subgroups, are recognized in subtribe Arinae (subfam. Aroideae tribe Areae).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1990.tb12558.x

出版商:Wiley    

年代:1990

数据来源: WILEY