Temporal and spatial patterns in flowering phenology were assessed for eight tropical African tree species. Specifically, the frequency and seasonality of flowering at seven sites in central Africa were determined using field data, graphical analysis and circular statistics. Additionally, spatial variation in the timing of flowering across species range was investigated using herbarium data, analysing the relative influence of latitude, longitude and timing of the dry season with a Bayesian circular generalized linear model. Annual flowering was found for 20 out of the 25 populations studied. For 21 populations located at the north of the climatic hinge flowering was occurring during the dry season. The analysis of herbarium collections revealed a significant shift in the timing of flowering with latitude for E. suaveolens, and with the timing of the dry season for M. excelsa (and to a lesser extent L. alata), with the coexistence of two flowering peaks near the equator where the distribution of monthly rainfall is bimodal. For the other species, none of latitude, longitude or timing of the dry season had an effect on the timing of flowering. Our study highlights the need to identify the drivers of the flowering phenology of economically important African tree species.

Many species are poorly known, with the sum of our knowledge represented by specimens in museums. For assessment of conservation status the most enigmatic and challenging species are probably those known only from a single specimen. We examine the potential persistence of such species using the orchid flora of Madagascar as a case study. We apply a statistical method that tests the likelihood of species presence in relation to the time when a species was collected and a measure of annual collection effort, calculated in three ways based on specimen collection over time. The results suggest that as of 2000 up to nine of the 236 orchid species known from a single specimen may be inferred to be extinct under at least one of the three methods of estimating collection effort and extinction. In addition, up to two additional species are likely to be extinct by 2018 assuming no new collections were made by that time. Substantial collection effort and/or additional evidence will be needed to reach a decision on the persistence of more recently observed species known only from a single collection. This represents a challenge for conservation practitioners.

Voucher specimens and herbarium collections provide the foundation for many aspects of research in the plant sciences. Available for study and verification by contemporary and future workers, voucher specimens promote reproducibility in scientific method because permanent records document identification, distribution, and interspecific and intraspecific variation of species. The utility and importance of voucher specimens and herbarium collections in supporting research in weed science are discussed, and the collection, preparation, documentation, storage, and shipment of voucher specimens are detailed.