Tropical forests occurring on white-sand soils have a unique structure and are famous for their endemism. Yet, no comprehensive floristic study has ever been undertaken in white-sand forests in the western Amazon. Here, we present the results of floristic inventories from 16 plots in seven sites from the Peruvian Amazon to investigate diversity, species composition, and endemism in white-sand forests. We compare our results to a large data set from terra firme forests from more fertile soils in the same region. We found that white-sand forest plots have extremely low average species diversity (41.5 species per 0.1-ha plot) and that white-sand plots have significantly different species composition from terra firme plots. We classify 114 species as endemic to white sand, with another 21 species that can be considered facultative specialists or cryptic endemics. These endemics and specialists are extremely dominant, accounting for more than 83% of the total number of stems surveyed in white-sand forest plots. We place our results in the context of the role of environmental heterogeneity influencing patterns of species diversity and the conservation of Amazonian forests.

We present a new generic classification of the largely Southern Hemisphere grass subfamily Danthonioideae. This classification is based on an almost completely sampled and well-resolved molecular phylogeny and on a complete morphological data set. We have attempted to delimit monophyletic genera (complicated by the presence of apparent intergeneric hybridization), which are diagnosable, as well as morphologically and ecogeographically coherent. We recognize 17 genera, including five new genera (Austroderia N. P. Barker & H. P. Linder, Capeochloa H. P. Linder & N. P. Barker, Chimaerochloa H. P. Linder, Geochloa H. P. Linder & N. P. Barker, and Tenaxia N. P. Barker & H. P. Linder), and two sections newly designated for Pentameris P. Beauv. (section Dracomontanum H. P. Linder & Galley and section Pentaschistis (Nees) H. P. Linder & Galley). Of the remaining 12 genera, the delimitations of seven are changed: Merxmuellera Conert is much reduced by the segregation of Geochloa, Capeochloa, and Tenaxia; Pentameris is expanded to include Prionanthium Desv. and Pentaschistis (Nees) Spach; Cortaderia Stapf is expanded by the inclusion of Lamprothyrsus Pilg., but reduced by the segregation of its New Zealand species into the new genus Austroderia; a large Rytidosperma Steud. is assembled out of Joycea H. P. Linder, Austrodanthonia H. P. Linder, Notodanthonia Zotov, Erythranthera Zotov, Pyrrhanthera Zotov, and Monostachya Merr.; and the species previously assigned to Karroochloa Conert & Türpe, Schismus P. Beauv., Urochlaena Nees, and Tribolium Desv. have been reassigned to only two genera. Finally, the Himalayan species of Danthonia DC. are transferred to Tenaxia and the remaining African species of Danthonia to Merxmuellera. The 281 species that we recognize in the subfamily are listed under their new genera, which are arranged in the phylogenetic sequence evident from the molecular phylogeny. The 100 necessary new combinations include: Merxmuellera grandiflora (Hochst. ex A. Rich.) H. P. Linder, Geochloa decora (Nees) N. P. Barker & H. P. Linder, G. lupulina (L. f.) N. P. Barker & H. P. Linder, G. rufa (Nees) N. P. Barker & H. P. Linder, Capeochloa arundinacea (P. J. Bergius) N. P. Barker & H. P. Linder, C. cincta (Nees) N. P. Barker & H. P. Linder, C. cincta subsp. sericea (N. P. Barker) N. P. Barker & H. P. Linder, C. setacea (N. P. Barker) N. P. Barker & H. P. Linder, Pentameris pra

Verbena L. (Verbenaceae) is represented by 44 species, mainly distributed in America, with two species distributed in temperate regions from both hemispheres: V. officinalis L. and V. supina L. South American species are morphologically different from North American species and are placed in two separate series: Verbena ser. Pachystachyae Schauer and series Verbena, respectively. In the present treatment, Verbena ser. Verbena taxa are described. This series includes 26 species, placed in three informal groups: Verbena, Hastatae, and Bracteosae. Detailed morphological descriptions are given for each taxon, as well as keys for their identification, illustrations, actualized synonymy with 56 new synonymized species (Appendix 3), and discussions of relationships between closely related taxa. Two new combinations are introduced: V. gracilescens (Cham.) Herter var. swiftiana (Moldenke) N. O'Leary and V. simplex Lehm. var. orcuttiana (L. M. Perry) N. O'Leary; nine species are lectotypified: V. bracteata Lag. & Rodr., V. bracteosa Michx. var. brevibracteata A. Gray, V. carolina L., V. domingensis Urb., V. officinalis var. gracilescens Cham., V. hastata L., V. hirsuta M. Martens & Galeotti, V. riparia Raf. ex Small & A. Heller, and V. urticifolia L. var. simplex Farw.; and six species are neotypified: V. ehrenbergiana Schauer, V. lasiostachys Link, V. roemeriana Scheele, V. simplex Lehm., V. spuria L., and V. xutha Lehm.

Podostemaceae, a family of plants restricted to river rapids and waterfalls, are widely reported to have a high degree of local species endemism. We tested this idea for Neotropical members of the family using historical records, herbarium holdings, personal field collections, and geographic information systems analyses. In contrast to estimates of endemism based on the landmark studies of P. van Royen (66%), we report 15%–37% based on current taxonomy. Examples of regional endemism, based on extent of occurence and longest geographic axis measures, are discussed for a subset of species. Major hydrographic regions (Amazon River System, Paraná River System) and major areas (eastern Brazil) are shown to possess largely unique podostemad floras. We propose rivers and river systems as the most appropriate units to assess endemism for Podostemaceae, and consider one-river and two-river endemics as narrowly distributed. Limitations in the current taxonomy are discussed relative to establishment of meaningful estimates of local species endemism. We provisionally apply IUCN assessment categories to Neotropical Podostemaceae and report that approximately one third of the species fall into one of three categories: Data Deficient (DD), Least Concern (LC), and Vulnerable (VU). Ten species are Critically Endangered (CR). Species of Podostemaceae are restricted to an environment that has experienced major human impacts—tropical rivers. Large dams make long reaches of rivers inhospitable. Expanded use of hydropower in Latin America will exacerbate the problem.

Hondurodendron C. Ulloa, Nickrent, Whitef. & D. Kelly, a new monotypic genus endemic to Honduras, is here described and illustrated. The new species, H. urceolatum C. Ulloa, Nickrent, Whitef. & D. Kelly, is a dioecious tree, distinguished by its minute flowers borne on densely tomentose inflorescences, unique anthers opening by three valves, and a characteristic fruit totally enveloped by the accrescent calyx, which projects beyond the fruit. A molecular analysis based on four genes (nuclear small subunit [SSU] ribosomal DNA [rDNA], chloroplast rbcL, matK, and accD) placed this genus in a clade with Aptandra Miers, Harmandia Pierre ex Baill., Chaunochiton Benth., and Ongokea Pierre in the family Aptandraceae Miers.