Showing papers in "Botanical Review in 2006"

Diversity and Distribution of Floral Scent

Abstract: A list of 1719 chemical compounds identified from headspace samples of floral scent is presented. The list has been compiled from some 270 published papers, including analyses of 991 species of flowering plants and a few gymnosperms, a sample including seed plants from 90 families and 38 orders. The compounds belong to seven major compound classes, of which the aliphatics, the benzenoids and phenylpropanoids, and, among the terpenes, the mono- and sesquiterpenes, occur in most orders of seeds plants. C5-branched compounds, irregular terpenes, nitrogen-containing compounds, and a class of miscellaneous cyclic compounds have been recorded in about two-thirds of the orders. Sulfur-containing compounds occur in a third of the orders, whereas diterpenes have been reported from three orders only. The most common single compounds in floral scent are the monoterpenes limonene, (E)-β-ocimene, myrcene, linalool, α- and β-pinene, and the benzenoids benzaldehyde, methyl 2-hydroxybenzoate (methyl salicylate), benzyl alcohol, and 2-phenyl ethanol, which occur in 54–71% of the families investigated so far. The sesquiterpene caryophyllene and the irregular terpene 6-methyl-5-hepten-2-one are also common and occur in more than 50% of the families. Orchidaceae are by far the best investigated family, followed by several families known to have many species with strongly scented flowers, such as Araceae, Arecaceae, Magnoliaceae, and Rosaceae. However, the majority of angiosperm families are still poorly investigated. Relationships between floral scent and pollination, chemistry, evolution, and phylogeny are briefly discussed. It is concluded that floral scent chemistry is of little use for phylogenetic estimates above the genus level, whereas the distribution and combinations of floral scent compounds at species and subspecific levels is a promising field of investigation for the understanding of adaptations and evolutionary processes in angiosperms.

Invasive Marine Algae: An Ecological Perspective

Abstract: The significance of marine algal invasion is undisputed in the global context; however, this topic has not received as much attention as it deserves. Although substantial evidence supports the fact of marine algal introduction and invasion, the underlying ecological principles need more attention to better explain such invasions. Marine algal invasions transcend national boundaries, so the problem must be considered an international problem. Commercial exploitation of invasive marine algae (and under this category we include deliberate introductions) should be undertaken, if at all, with great care and with a full understanding of all aspects of the biology and ecological consequences of the new exotic species. The aim of this article is to define algal invaders from a marine ecosystem standpoint and to discuss the different vectors, their dispersal patterns, and mechanisms of their dominance in their naturalized or introduced range.

The Evolution of Gender-Biased Nectar Production in Hermaphroditic Plants

Abstract: The evolution of secondary sexual floral traits may be driven by selection through male or female reproductive success. Even so, the gender-biased function of a floral trait is often unapparent because secondary sexual traits and primary sexual organs of both genders co-occur within most bisexual flowers. Within dichogamous plants, however, secondary sexual traits may be unambiguously expressed in association with the primary sexual organs of one gender, making these species uniquely suited to studies of natural and sexual selection on floral traits. The objectives of this article are to summarize patterns of gender-biased nectar production and to critically explore theories relevant to its evolution. We list 41 species with gender-biased nectar production and provide two sets of adaptive hypotheses for the trait: sexual selection hypotheses and inbreeding avoidance hypotheses. We formulate these hypotheses using sexual selection theory in plants and the literature that relates pollinator foraging to plant inbreeding. We also consider explanations based on resource trade-offs, enemies, and genetic correlations. Support for the sexual selection and inbreeding avoidance hypotheses is provided by only a few well-studied species. We outline a series of experiments that should facilitate sorting among hypotheses. Plants with gender-biased nectar production are likely to provide unique insights into the roles of natural and sexual selection in the evolution of floral traits.

Research in the Garden: Averting the Collections Crisis

Abstract: Botanic gardens and arboreta are a vibrant part of the natural history collections community, serving society in areas such as education, recreation, and research. Unfortunately, at the present time dwindling support and advocacy for collections-based research has placed these institutions in the midst of a collections crisis. In this review, I assess the historical importance of living plant collections in supporting research, examine why their research potential is currently unmet, and provide a series of rationales in support of collections-based research. To avert this crisis several things must occur, the most basic of which is stronger advocacy for living collections and the research derived from them. Traditional views of collections management need to be evaluated under new light and the pool of researchers expanded. Formal, on-site programs are not required for collections to be used for research, as off-site scientists can make great contributions. Toward this end, collaborative links b...

Morphology and Anatomy of Palm Seedlings

Abstract: A historical survey of studies of seedling morphology and anatomy in the palm family is given. The traditional three germination types—adjacent ligular, remote ligular, and remote tubular—that have been commonly recognized are reevaluated. The study includes seedlings of 63 species, representing the six subfamilies of palms. Morphological characteristics of germination patterns and the anatomy of the eophyll are described. The results of this survey show that germination types determined by the length of the hyperphyll (cotyledonary petiole) are not completely valid. Instead, a combination of characters such as primary root orientation, coleoptile length, number of cataphylls, and eophyll plication correspond to the most recent classification of the family, and represent a better way of describing germination.

Xeric Limestone Prairies of Eastern United States: Review and Synthesis

Abstract: Xeric limestone prairies (XLPs) are open, nonforested areas in which herbaceous plant communities occur on shallow, rocky soils derived from calcareous substrates. These grasslands are characterized by dominance of C4 perennial grasses (particularly Schizachyrium scoparium) and are distributed in eastern United States from Missouri and Pennsylvania south to Arkansas and Georgia. XLPs occur in the Ozark Plateaus, Central Lowland, Interior Low Plateaus, Appalachian Plateaus, Ridge and Valley, and Coastal Plain physiographic provinces, and they are developed on Alfisols, Ultisols, Mollisols, Inceptisols, and Vertisols derived from Paleozoic limestones (also Eocene), dolomites, and calcareous shales. The C4 perennial prairie grass S. scoparium is the characteristic dominant taxon in XLPs of eastern United States. However, C3 perennial forbs are dominant in some sites, and C4 annual grasses (Sporobolus spp.) may be locally dominant in shallow-soil-zone microsites. Thirteen taxa apparently are endemic,...

Microspore Morphology of Isoetes Species (Lycophyta) from Southern South America

Abstract: Microspores of the 24 species of Isoetes that grow in southern South America were analyzed under a light microscope and scanning electron microscope. The microspores are monolete, elliptic in polar view, 30–40 µm long, and 20–25 µm wide. A background with various characteristics is seen on each surface. A supra-laesural expansion is present. The perispore is ornamented and has a perforated background. In section, it has a lacunose structure. The exospore is smooth, and it has a compact structure in section. The studied species could be divided into three groups by their perispore ornamentation: equinate, rugulate, and tuberculate. Microspore size was positively correlated with increasing ploidy level, and larger microspores were associated with terrestrial habitats. A convergence in ornamentation was found between spores produced by the studied species and those that grow in regions outside of the area under study.

Microspore Morphology of Isoetes Species (Lycophyta) from Southern South America. Part II. TEM Analysis of Some Selected Types

Abstract: The microspores of Isoetes escondidensis, I. gardneriana, I. herzogii, I. pedersenii, and I. savatieri were analyzed with transmission and scanning electron microscopy. The selected species were found to be representative of the diversity found in 24 taxa previously studied that grow in southern South America. The sporoderm is similar in the five types and is composed, from the outside to the inside, of perispore, para-exospore, exospore, and endospore. In I. escondidensis, I. gardneriana, I. herzogii, and I. savatieri, the perispore is lacunose, whereas in I. pedersenii, it is camerate. The para-exospore is formed of large superimposed and fused bars, which are more numerous and thicker in immature spores. The exospore shows uniform characteristics and a strongly contrasted cover. It has pluristratified zones on both sides of the aperture. The presence of radial rodlets between the para-exospore and exospore and in the supra-apertural chamber is described here for the first time. The endospore h...

Chlorophyll b-Containing Oxygenic Photosynthetic Prokaryotes: Oxychlorobacteria (Prochlorophytes)

Abstract: The major ultrastructural and pigment characteristics of three chlorophyll b-containing photosynthetic prokaryote genera, Prochloron, Prochlorothrix, and Prochlorococcus, are summarized. Aspects of their ecology are reviewed, as are also the major findings of comparisons among the three genera, and between them and the cyanobacteria, based on analyses of nucleotide sequences. The information summarized is discussed to assess how closely the three genera are related and whether they form a natural taxonomic grouping within the cyanobacteria. It is concluded that, although much of the evidence points to substantial differences among the three genera, the convenience of keeping them together as a group, namely, Oxychlorobacteria (formerly Prochlorophyta), outweighs certain inconsistencies revealed by analysis of a range of objective criteria. Current views on the possible significance of the group to considerations of the evolution of green chloroplasts are also presented.