(American Journal of Botany. ;90:0.)
© Botanical Society of America, Inc.
Flowering patterns in tropical rain forest trees
In two papers in this issue Bawa, Grayum, and Kang, and Kang and Bawa report the results of observations of flowering in more than 300 tree species at La Selva, Costa Rica. They analyzed the relationship among flowering frequency, seasonality, and duration, and between these parameters and several ecological variables. The patterns that emerged from the analyses are sure to raise new questions and interest about phenology beyond the simple description of when something flowers and for how long. Data on the relationships between pollinators (and other variables) and phenology may be particularly valuable in assessing how animals and plant resources are structured in tropical environments, at least in trees. The community approach used by the authors is especially noteworthy.(see
p. 865
and
p. 877
)
Septate vs. aspetate anther development in the Annonaceae is the focus of a paper by Tsou and Johnson. While tetrasporangiate, nonseptate anthers with a bithecal organization is the norm in angiosperms, some genera in the Annonaceae having extremely large pollen shed in units of four or sometimes even 32 grains (see cover) possess septa that separate the grains into chambers within each anther. While the initial interest in these septate anthers was to establish their reliability as a character for phylogenetic analyses, the authors' literature review clearly shows that there is a real discrepancy in the reporting of these anther types in the Annonaceae that must be resolved prior to any use of the character for that purpose. The authors found that the septal tissues of all species investigated were formed by the same developmental pathway, despite variability in appearance. One reviewer notes that "consistently exquisite" micrographs highlight this paper.
(see p. 832)
Michael Sanderson makes a thoughtful response to a recent paper by Heckman et al. (Science 293: 1129-1133) that suggested an origin for land plants in the Precambrian, about 250 million years before any corresponding data from the fossil record. Sanderson's larger, independent data set comes to the opposite conclusion, raising questions about Heckman et al.'s reliance on molecular clocks. Sanderson's analysis using 27 plastid protein-coding genes, a calibration point nearer to the origin of land plants, and methods that do not assume a molecular clock resulted in estimates for the age of land plants much more in line with those from the fossil record. Thus, methods that allow for rate heterogeneity indicate the fossil record is able to provide reasonable divergence times.
(see p. 954)
While it has been known that leaf surface traits may be involved in mediating both biotic and abiotic interactions, the majority of studies have focused on only one aspect, i.e., they have been either ecophysiological or defense oriented and have thus ignored the possible interaction between biotic attackers and the response of leaves to the physical environment. The combination of laboratory, greenhouse, and field experiments reported by Bradley, Gilbert, and Parker is remarkable in examining how leaf surface traits mediate the influence of the abiotic environment on pathogen attack. Specifically, the authors focus on the adaptive role of leaf water repellency in 18 sympatric clover species across a moisture gradient, and find that laboratory experiments provide a mechanistic explanation for counterintuitive patterns in the field. This area of adaptive plant biology is just beginning to be unraveled and has a strong potential for agricultural and horticultural applications.
(see p. 867)
