Pollination biology is an especially important component of the overall ecological setting of a plant species since it has direct implications on reproductive success. Over time, a typological approach to classifying flower—pollinator interactions in the form of “floral syndromes” has been developed, and considerable predictive power is traditionally ascribed to these syndromes. Recent studies have increasingly questioned both the predictive value of the syndrome concept, as well as the underlying notion of increasing specialization amongst flower-pollinator interactions. The casual discovery that the seemingly ornithophilous flowers of the globose to shortly columnar South American cactus Denmoza rhodacantha (Cactaceae: Cactoideae: Cereeae: Trichocereinae) are visited by solitary pollen-collecting halictid bees, rather than the expected hummingbirds, adds another example to the growing body of mismatches between floral syndrome and observed pollinator.

Astrophytum coahuilense and Astrophytum capricorne var. senile have partly sympatric distributions in southern Coahuila and adjacent Zacatecas, Mexico. The apparent absence of natural hybrids in areas of sympatry has been noted by several authors, leading to speculation concerning the mechanisms of reproductive isolation. Experimental crosses between the two species revealed prezygotic isolating mechanisms in some cases and postzygotic mechanisms in others. Several different results were obtained from the cross-pollinations: 1) fruit was not produced and the ovules in the ovary of the floral remnant showed no development; 2) fruit contained incompletely developed, mostly non-germinant seeds; 3) apparently normal seed was produced, but many of the hybrid seedlings manifested morphological anomalies and mortality was high (>97%) due to chlorophyll deficiency. A series of experimental crosses between A. coahuilense and several allopatric taxa of the A. capricorne group revealed only postzygotic isolation. The discovery of prezygotic isolation in some trials between the sympatric taxa is consistent with theoretical expectations. Postzygotic isolating mechanisms are costly in terms of gametic wastage and therefore natural selection should favor the evolution of one or more prezygotic barriers between the interacting species. The varied results of the experimental crosses between A. coahuilense and A. capricorne var. senile (postzygotic isolation in some cases, prezygotic isolation in others) are possibly explained by differing histories of interaction between populations of the two species.

The easternmost population of Opuntia fragilis occurs on a remote rock outcrop in Eastern Ontario. The Kaladar population is located almost 1,000 km away from its nearest neighbor and has recovered from previous vandalism. Recent visits to this site have discovered a plant producing flowers with viable pollen, but without carpels.

We performed karyotype analyses on Hylocereineae species. Epiphyllum phyllanthus, Selenicereus aff. megalanthus and S. aff. setaceus were diploid, with 2n = 22 chromosomes, whereas S. setaceus was tetraploid. Karyotypes were symmetrical with the formulas 11 m in E. phyllanthus, S. aff. setaceus and S. aff. megalanthus, and 22 m in S. setaceus. Chromosomes were small with the average length being 2.76 μm. Diploid species had two terminal satellites and tetraploids had four terminal satellites. The only bands associated with NOR were found in all specimens and were CMA /DAPI^- bands. Pericentromeric heterochromatin was found in S. aff. megalanthus. The locations of the 18-5.8-26S rDNA sites in all species coincided with CMA bands. The signals of the 5S rDNA gene were located in paracentromeric regions on at least one locus in all taxa. Additional 5S loci were found in all species, with the exception of E. phyllanthus. One pair of 5S sites was co-localized with 18-5.8-26S loci in S. aff. setaceus and tetraploid S. setaceus, which is a new position for Cactaceae. The 18-5.8-26S rDNA loci seem to be highly conserved, in contrast with the 5S rDNA loci that were scattered throughout the genome.

We evaluated the pharmacological consequences of tissues other than crown being included with harvested peyote. Mean mescaline concentrations were determined for crown, non-chlorophyllous stem, and root, using mature individuals from the same population in South Texas. Samples of each tissue—crown, non-chlorophyllous stem, and root—were taken from each of 13 individual plants. Samples were dried, triturated, defatted, and extracted with methylene chloride, using an acid-base aqueous wash to recover the alkaloids. The concentration of mescaline in each sample was determined by HPLC. The average mescaline concentration in non-chlorophyllous stem was an order of magnitude lower than that in crown, whereas the mescaline concentration in root was two orders of magnitude lower than that in crown. These results show that non-chlorophyllous stem is a poor source of mescaline, and root is an extremely poor source. These results have important implications for conservation, suggesting that non-traditional harvesting of peyote for religious or medicinal use involving the cutting of non-chlorophyllous tissue are contributing to the death of plants and the subsequent failure to regenerate new crowns. Therefore, this practice should be reevaluated by peyote harvesters and users.

We evaluated type of stomata, as well as differences in stomatal frequency in three areas of the plant (apical, middle and basal) under two culture conditions (in vitro and ex vitro), in four cactus species (Opuntia ficus-indica, Hylocereus undatus, Escontria chiotilla and Mammillaria petterssonii). We measured stomatal density (SD) and the stomata index (SI) for both factors, plant area and culture condition. Stomata typology were cyclocytic, tetracytic or opuntioid type in O. ficus-indica and parallelocytic type in E. chiotilla, H. undatus and M. petterssonii. It was observed that SD was higher ex vitro than in vitro in H. undatus and M. petterssonii, but the opposite was true for O. ficus-indica and E. chiotilla. The apical region had the highest SD both in in vitro and ex vitro, and the interaction between culture condition and explant areas was highly significant, implying that the impact of culture type is different for each distinct stem area.

Simple leaves are usually conceptualized as terminal organs that cannot develop new roots or shoots. However plants with succulent or semi-succulent leaves in many unrelated families defy this rule. They do so by differentiating leaf parenchyma — which are probably often phloem parenchyma or companion cells, the two of which are often indistinguishable — into new root and shoot apical meristems. Succulent and semi-succulent leaves can survive longer than non-succulent leaves once detached from shoots of their parent plant, possibly enabling them to differentiate and establish a root system before desiccation and/or starvation. Curiously, almost no succulent plants have compound leaves, even though compound leaves are often considered to have properties of both stems and leaves and hence theoretically should have the capability of developing new structures, such as new root and shoot meristems. I discuss some testable predictions arising from these notions and ask whether differences between ability to regrow roots and shoots from detached leaves of monocots versus eudicots is better explained by reticulate versus parallel venation or phylogenetic constraints.

Sedum piaxtlaense is described as a new species based on a collection in the Rio Piaxtla Canyon, growing in tropical deciduous forest in the Sierra Madre Occidental near the border of the Mexican states of Durango and Sinaloa. This new species belongs into the section Sedastrum (Rose) A. Berger whose distinctive morphological characteristics are basal rosettes, generally pubescent leaves, concave carpel base, usually paniculate inflorescences, and white corollas, the only exceptions being Sedum glabrum and S. jarocho which do not show any pubescence in their floral structures. S. piaxtlaense is apparently closely related to S. hintonii and S. mocinianum from which it differs in the laxer rosettes, concave leaves of larger diameter, as well as a shorter inflorescence with up to eight flowers per cincinnus and large pedicels, and its distribution in another biogeographical province.

In 1978, Howard Scott Gentry published his second monograph on the genus Agave focusing on the plants of the peninsula of Baja California, México, and the related species in the group Deserticolae in the US and Sonora. We revisit Gentry's work with an emphasis on revising the genus and its taxonomic arrangement and including several recently described species from this Mexican peninsula known for its high plant endemism. A total of 23 Agave taxa occur on the peninsula, 22 of which are endemic. We change Gentry's treatment of four groups into six sections formally defined to better segregate species based on shared inflorescence characteristics. We eliminate one variety, revert one variety to species status, change two species to subspecies or varieties, and reduce one subspecies to a variety. We present high spatial resolution maps of the distribution of these species as well and correct some of the previous identifications of herbarium specimens. Extensive field work suggests that taxonomic problems remain in the Agave sobria complex of the Sierra de la Giganta, where as many as three additional taxa could be described from the array of variation we observed. As well, the distributional overlap of Agave avellanidens and Agave shawii ssp. goldmaniana remains problematic owing to similar vegetative characteristics but greatly differing inflorescences.