Field botanists often have clever ways to identify species that are difficult to distinguish from each other without a microscope or reference to herbarium specimens. Usually the scientific basis or mechanism of such a

Leaf nectary of Prockia crucis P. Browne ex. L. (Salicaceae) with a drop of sucrose-rich, high-energy nectar, which may be attractive to visitors. Some species of aggressive ants get nectar from extrafloral nectaries, meanwhile protecting the plant's leaves. This interaction may be an important strategy to enhance the adaptive success of the species. These highly structured nectaries are similar to the salicoids teeth of the Populus and Salix species, lending strong support to the phylogenetic proximity of these clades.

For further detail: see Thadeo et al.

Stem cross section of Pereskia guamacho, a member of the eight-species cactus lineage hypothesized to be sister to the remaining 1800 or so species of Cactaceae. Pereskia guamacho is a leafy, dry-forest tree lacking many anatomical traits, such as stem succulence, mucilage cells, delayed periderm, and stem stomata, that are highly conserved in most other cacti. Rather than the evolution of a single

Contrary to conventional wisdom, the life cycle of Arabidopsis thaliana does not consist of a vegetative rosette that is the source of carbon production followed by a reproductive inflorescence that is a carbon sink. Earley et al. show instead that the inflorescence contributes much of the lifetime carbon gain, from 36 to 93%, depending on the genotype, and with much less water lost per unit carbon gained compared to the rosette. They suggest that the switch from rosette to inflorescence is an ontogenetic niche shift that allows the plant to successively exploit the warm air at the soil boundary during the cool season and escape into the freely moving air in warm season. This shift also results in a more water-use efficient plant during the warm season.

For further detail, see: Earley et al.

Stanleya pinnata (prince's plume) can hyperaccumulate the toxic element selenium (Se) up to 0.5% of its dry mass in its natural habitat in the western United States. In a 2-year manipulative field experiment to test whether S. pinnata uses Se as an elemental defense against one of its native mammalian herbivores, the blacktailed prairie dog (Cynomys ludovicianus), plants with high Se concentrations had higher survival rates and less herbivory than low-Se counterparts when planted in black-tailed prairie dog towns. These results give better insight into the evolution of plant Se hyperaccumulation, suggesting a role for herbivory as a possible selection pressure. From an applied perspective, plants that accumulate Se may be cultivated for phytoremediation or as fortified foods, and this study helps assess the associated risk of Se moving up the food chain.

For further detail, see: Freeman et al.

Numerous complex mathematical theories have been proposed to explain why annual growth rates of plants scale as the 3/4 power of total body mass, why total leaf mass per plant scales as the square of trunk diameter, and why a host of other widely reported ecological phenomena occur. In this issue, Hammond and Niklas unveil a new computer model, called SERA (for spatially explicit reiterative algorithm), which accurately predicts these and many other scaling relationships as plants are forced to conform mathematically to a few very simple physical principles while they compete for light and space. In each SERA simulation, tree canopies are depicted as thinshelled hemispheres and trunks are modeled as simple, untapered cylinders that increase in girth as simulated plants age. A hypothetical landscape is randomly seeded with a specified number of propagules and monitored during every growing season to assess biomass- and age-dependent allometric relationships. A graphic module allows a population or community to be observed at any stage in its growth as old plants die and new ones propagate. In this image, the observer is standing at ground level and looking up into a forest composed of a single species mathematically modeled to mimic the allometry of a population of Abies alba.

For further detail, see: Hammond and Niklas

Longitudinal section of developing caryopsis of maize ancestor, teosinte (Zea mays ssp. parviglumis, caryopsis diameter cca. 3 mm). Teosinte plants differ significantly from domesticated maize Zea mays ssp. mays. Teosinte plants have many lateral branches with terminal male inflorescences, which closely resemble maize tassels, and small female inflorescences or

Reproductive stem of Monotropsis odorata (sweet pine sap; Ericaceae), a nonphotosynthetic plant endemic to the southeastern United States. As a myco-heterotroph, M. odorata obtains carbon resources from associated mycorrhizal fungi and has a highly reduced vegetative morphology consisting of an underground root mass that produces one to many diminutive reproductive stems (3.5