A revised assessment of Croton L. sect. Geiseleria (A. Gray) Baill. is provided. The section as now circumscribed includes 84 species ranging across warm areas of the Americas. A nuclear ITS phylogeny of 150 accessions from 83 species and a chloroplast trnL-F phylogeny of 89 accessions from 65 species were generated to confirm correct phylogenetic placement of the species and to determine if any species previously included in the section should now be excluded. Seven new species are described, and we present a taxonomic synopsis that lists all currently accepted species along with their synonyms, distributions, and pertinent comments. We also recognize four subsections within Croton sect. Geiseleria and list their corresponding species. Based on both morphological and molecular criteria, we now recognize C. lagunillae Croizat as a distinct species, rather than as a variety of C. guildingii Griseb. (now treated as C. suavis Kunth), and we treat C. ramillatus Croizat var. magniglandulifer V. W. Steinm. as a species, C. magniglandulifer (V. W. Steinm.) B. W. van Ee. We also exclude C. tetradenius Baill. from Croton sect. Geiseleria (A. Gray) Baill. along with related species such as C. pulegiodorus Baill. and C. leptobotryus Müll. Arg., which are either members of Croton sect. Adenophylli Griseb. or else may merit new sectional status. We also exclude C. waltherioides Urb., although it is not clear to which section of Croton it belongs.

The forests of Amazonia are among the most biodiverse plant communities on Earth. Given the immediate threats posed by climate and land-use change, an improved understanding of how this extraordinary biodiversity is spatially organized is urgently required to develop effective conservation strategies. Most Amazonian tree species are extremely rare but a few are common across the region. Indeed, just 227 ‘hyperdominant’ species account for >50% of all individuals >10 cm diameter at 1.3 m in height. Yet, the degree to which the phenomenon of hyperdominance is sensitive to tree size, the extent to which the composition of dominant species changes with size class and how evolutionary history constrains tree hyperdominance, all remain unknown. Here, we use a large floristic dataset to show that, while hyperdominance is a universal phenomenon across forest strata, different species dominate the forest understory, midstory and canopy. We further find that, although species belonging to a range of phylogenetically dispersed lineages have become hyperdominant in small size classes, hyperdominants in large size classes are restricted to a few lineages. Our results demonstrate that it is essential to consider all forest strata to understand regional patterns of dominance and composition in Amazonia. More generally, through the lens of 654 hyperdominant species, we outline a tractable pathway for understanding the functioning of half of Amazonian forests across vertical strata and geographical locations.

Croton flavens shares a general morphology with multiple species throughout Croton sec-tion Adenophylli, which has complicated the application of names to these taxa. We generated nuclear (ITS) and chloroplast (trnL-F) phylogenies of C. sect. Adenophylli in order to identify the phylogenetic placement of C. flavens and morphologically similar species. Based on these phylogenies, we recognize six subsections within the section, two of which (C. subsects. Adenophylli and Velamea) required new combinations, three others (C. subsects. Caribaeus, Laceratoglandulosus, and Meridionalis) are newly described, and one (C. subsect. Pungentes) was previously described. Croton flavens is restricted to the islands of the West Indies, extending from the Bahamas to Trinidad, but absent from the Leeward Antilles. It appears to be rare at the extremes of its range in the Bahamas and Trinidad, but otherwise it is often a ubiquitous member of dry, shrubby vegetation of many Caribbean islands. Within C. flavens we recognize a widespread typical variety and C. flavens var. pallidus from Hispaniola and Cuba.

Abstract Croton kinondoensis, a new species from Kenya, is described and illustrated here with photographs. It is found in the sacred Kaya Kinondo Forest, one of the last remaining coastal forests patches in Kenya. Its morphology and systematic position based on ITS and trnL-F DNA sequence data clearly place it within the Adenophorus Group of Croton, a clade of ca. 15 species otherwise known only from Madagascar and the Comoros Archipelago. Its closest affinities appear to lie with Croton mayottae, from the island of Mayotte, and C. menabeensis, from northwestern Madagascar. This new species likely represents an independent dispersal of Croton from Madagascar to mainland Africa.

In this chapter, we update our knowledge of the flora of the summits and upper slopes of the tepuis of the Guiana Shield. These mountains are collectively known as Pantepui, which is considered a biogeographic province and recognized as a center of plant diversity and endemism in the Neotropics. We analyze the current floristic data and emphasize the main diversity and biogeographic patterns across tepuis. Our main focus is on vascular plants, but we also cover the available information on bryophytes. For vascular plants, we report 2579 species known from Pantepui, of which 34%–40% are endemic or nearly endemic. We also review relevant phylogenetic studies covering Pantepui taxa and highlight the main findings regarding the biogeographic history of the flora. This update provides a new starting point for future research in systematics, biogeography, and conservation of this unique Neotropical mountain system.

During the last 40 years, one of the most widespread and conspicuous succulent trees in East and north-east Africa has been referred to as Euphorbia candelabrum Kotschy or as E. candelabrum Tremaux ex Kotschy. This name is a later homonym of E. candelabrum Welw., and consequently it is illegitimate. The species to which the name E. candelabrum Kotschy has been widely applied is shown to be conspecific with E. ingens, which occurs from southern Ethiopia to subtropical South Africa.

Croton is the second largest genus of Euphorbiaceae with about 1200 tropical species. Of these, over 715 species are native to the Americas and have been assigned to 31 sections. Croton sect. Geiseleria includes about 80 species distributed from the United States to Argentina; they are especially diverse in Brazil, where about two thirds of its species occur. Many specimens from this section have been erroneously identified and require proper typification. We present a taxonomic synopsis of C. sect. Geiseleria for Brazil, based on the analysis of over 2000 specimens from 60 herbaria and our own collections from dozens of excursions to multiple regions of the country. Fifty species in the section are recognized here for Brazil, 37 of them endemic to the country, among which C. seccoi is described as new to science. Three species (C. carinatus, C. catariae, and C. mollis) are newly transferred to the section based on morphological analysis. Twenty-seven new synonyms, 70 lectotypes and one neotype are proposed. All of the species are included in an identification key, and then comments on their geographic distributions, habitats, phenologies, conservation status, and diagnostic characteristics are provided. Finally, distribution maps, original illustrations, and photographs are provided for most of the species.

Ongoing studies of Neotropical Euphorbiaceae have uncovered a surprising number of new species belonging to Croton L. sect. Cleodora (Klotzsch) Baill., one of the better studied Glades in the genus. Here we describe six new species and reclassify three others that were either misplaced to section or regarded species of unknown phylogenetic affinity in previous studies. The new species are all from South America, and five of them are restricted to the Amazon region. We update the most recent taxonomic revision of Croton sect. Cleodora by providing a new taxon list and an identification key for the 27 currently recognized species. Sixteen species occur in lowland forested areas of the Amazon basin. Our finding calls attention to the Neotropics, and the Amazon region in particular, where information about the flora and species geographic ranges is still incomplete, even for relatively well-studied plant groups.

Woody perennial plants on islands have repeatedly evolved from herbaceous mainland ancestors. Although the majority of species in Euphorbia subgenus Chamaesyce section Anisophyllum (Euphorbiaceae) are small and herbaceous, a clade of 16 woody species diversified on the Hawaiian Islands. They are found in a broad range of habitats, including the only known C-4 plants adapted to wet forest understories. We investigate the history of island colonization and habitat shift in this group. We sampled 153 individuals in 15 of the 16 native species of Hawaiian Euphorbia on six major Hawaiian Islands, plus 11 New World close relatives, to elucidate the biogeographic movement of this lineage within the Hawaiian island chain. We used a concatenated chloroplast DNA data set of more than eight kilobases in aligned length and applied maximum likelihood and Bayesian inference for phylogenetic reconstruction. Age and phylogeographic patterns were co-estimated using BEAST. In addition, we used nuclear ribosomal ITS and the low-copy genes LEAFY and G3pdhC to investigate the reticulate relationships within this radiation. Hawaiian Euphorbia first arrived on Kaua`i or Ni`ihau ca.5million years ago and subsequently diverged into 16 named species with extensive reticulation. During this process Hawaiian Euphorbia dispersed from older to younger islands through open vegetation that is disturbance-prone. Species that occur under closed vegetation evolved in situ from open vegetation of the same island and are only found on the two oldest islands of Kaua`i and O`ahu. The biogeographic history of Hawaiian Euphorbia supports a progression rule with within-island shifts from open to closed vegetation.

We describe and illustrate four new species of dragon's blood trees (Croton sect. Cyclostigma) from western South America. Three of the species, Croton beckii from Bolivia and Peru, C. camposii from Peru, and C. santamartensis from Colombia, grow in montane Andean forest, whereas C. tumbesinus occurs in dry forest of the Tumbes/Piura ecoregion of western Ecuador and Peru. The characters that place them in Croton sect. Cyclostigma include the arborescent habit, the presence of reddish to yellowish latex, an indument of stellate trichomes, conspicuous and persistent stipules, acropetiolar/basilaminar nectary glands, and terminal inflorescences with bisexual cymules at the base. These new species give additional support for the Andean region being the main center of diversity of this Neotropical Croton lade, as well as being a region whose biodiversity knowledge is still incomplete.

Croton is one of the most diverse genera of flowering plants in Madagascar, with > 150 endemic species encountered in nearly all vegetation types. This study focuses on the evolutionary history of Croton in the western Indian Ocean region (WIOR), which includes Madagascar, the Comoro Islands and the Mascarene Islands, and aims to resolve species relationships and the biogeographic history of the genus there. We obtained nuclear ribosomal internal transcribed spacer and plastid (matK, trnH-psbA and trnL-F) sequence data for 71, or close to half, of the Croton spp. in the WIOR and 15 other Old World species and seven New World species. We analysed them phylogenetically using Bayesian and maximum likelihood criteria and performed an ancestral state reconstruction of their geographical distributions. Our results show general support for a single origin of Croton on Madagascar from Africa. This was followed by an extensive radiation into nearly all available habitats in Madagascar and subsequent dispersal events out of Madagascar, including two back colonizations to Africa, one or more dispersals to the Comoro Islands and a single dispersal to the Mascarene Islands.

All published names of Croton from Madagascar, the Comoros, and the Mascarenes are treated here. We indicate which names are currently accepted (123 native species and 1 introduced), which ones we consider to be heterotypic synonyms (188), which ones are doubtful (25), and which ones should be excluded (5). We newly designate lectotypes for 108 names, and epitypes for C. anisatus Baill., C. nobilis Baill., and C. submetallicus Baill. A total of 133 names are newly treated as synonyms. One new combination is made, Croton basaltorum (Leandri) P.E.Berry for C. antanosiensis var. basaltorum Leandri, and one new name is proposed, Croton toliarensis B.W.vanEe & Kainul. for C. tranomarensis var. rosmarinifolius Radcl.-Sm.

Crotoneae comprises six genera, of which Astraea, Brasiliocroton, Croton, Sagotia and Sandwithia all occur in Brazil. This tribe needs study because it is morphologically diverse, poorly known taxonomically and has numerous species in need of lectotypification, particularly Croton, the largest genus with over 1200 species. We present here the taxonomic treatment for the representatives of Crotoneae occurring in Chapada dos Veadeiros, Goias, Brazil, one of the best preserved areas of the Cerrado phytogeographic domain with high levels of plant endemism. The study is based on monthly collections made from January 2012 to March 2016, consultations of collections from herbaria CEN, IBGE, UB and UFG, and review of pertinent literature. Thirty five species are recognized, 33 of which belong to Croton and two to Astraea. Seven of these constitute new records for Goias State, nine are illustrated for the first time, and four have their descriptions revised. Additionally, keys to identify the studied taxa, descriptions with comments on geographic distribution, habitat, morphological relationships, flowering period and fruiting and maps, and illustrations for 34 of the 35 species recorded and images for 29 of them are provided, as well as five synonymizations, 17 lectotypifications and three second step lectotypifications.

Saxofridericia brasiliensis P.E.Berry & Krahl, a new species of Saxofridericia subgenus Acrotheca, is described and illustrated. It is most closely related to Saxofridericia aculeata Körnicke, but differs in its entire-margined leaves and narrower leaf blades. It is so far known only from white-sand campina vegetation north of Manaus along the Caracaraí highway in Amazonas State, Brazil.

The cataloging of the vascular plants of the Americas has a centuries-long history, but it is only in recent decades that an overview of the entire flora has become possible. We present an integrated assessment of all known native species of vascular plants in the Americas. Twelve regional and national checklists, prepared over the past 25 years and including two large ongoing flora projects, were merged into a single list. Our publicly searchable checklist includes 124,993 species, 6227 genera, and 355 families, which correspond to 33% of the 383,671 vascular plant species known worldwide. In the past 25 years, the rate at which new species descriptions are added has averaged 744 annually for the Americas, and we can expect the total to reach about 150,000.

This paper provides a revision of the species of Croton L. (Euphorbiaceae) from northern Madagascar (mainly Antsiranana and northern Mahajanga Provinces) and Mayotte in the Comoros Archipelago that bear glands on the undersides of the leaves. This includes members of the Adenophorus Group as well as two species that do not belong to that group, namely Croton nudatus Baill. and Croton stanneus Baill. Croton nudatus has been a problematic name since its publication due to the leafless state of its type. We were able to match the type with material recently collected near the type locality, and we provide an amended description for this species. Croton stanneus is another previously poorly understood species, which is actually one of the most widespread species of Croton in Madagascar. We also re-evaluate species delimitations in members of the Adenophorus Group from northern Madagascar and Mayotte, and we describe three new species, Croton mayottae P.E. Berry & Kainul., Croton orangeae Kainul. & P.E. Berry, and Croton sahafariensis Kainul. & P.E. Berry. Croton loucoubensis Baill. is resurrected from synonymy, and nine other species names and eight varieties are reduced to synonymy under Croton adenophorus Baill., Croton loucoubensis, Croton nudatus, Croton scoriarum Leandri, Croton stanneus, or Croton tsiampiensis Leandri. Full descriptions are provided for these species as well as for Croton bathianus Leandri, another misunderstood species in the group. A key to the seven species of the Adenophorus Group and the two look-alikes from northern Madagascar and Mayotte is provided. An epitype is designated for Croton nudatus, and lectotypes are designated for Croton adenophorus, Croton bathianus, Croton loucoubensis, Croton scoriarum, Croton stanneus, and Croton tsiampiensis.

Croton crossolepis is newly described and illustrated. It is a shrub or small tree endemic to southwestern Madagascar near Toliara and is distinguished by a mixture of stellate and lepidote trichomes, with most of the lepidote ones having fringed margins and partially free, stiff rays that can make it adhere to surfaces like clothing when they come into contact. The inflorescences are pseudoterminal and spicate in appearance, with numerous flowers subtended by acicular bracts that are longer than the buds. It has larger leaves than most Croton species that occur in the semi-arid southwestern scrub and spiny forests nearby in the country, and it is apparently quite rare and subject to ongoing decline, warranting a conservation assessment of Vulnerable.

Two species of Croton L. (Euphorbiaceae) previously reported only from their type specimens, Croton chapelieri Baill. and Croton vatomandrensis Leandri, are reevaluated here and found to be geographically widespread along the eastern coastline of Madagascar. We provide updated descriptions, lists of selected additional specimens, distribution maps, and photographs of both species. We also designate an epitype for Croton chapelieri and a lectotype for Croton vatomandrensis. Croton chapelieri was the source of considerable taxonomic confusion, and we treat as synonyms here for the first time Croton aymoninorum Leandri, Croton louvelii Leandri, Croton daphniphylloides Radcl.-Sm., Croton daphniphyllum Radcl.-Sm., Croton daphniphyllum var. hirsutus Radcl.-Sm., and Croton rhododendroides Radcl.-Sm. Croton chapelieri var. longepetiolata Radcl.-Sm. is considered to be a synonym of Croton submetallicus Baill. With our improved understanding of the geographical ranges of Croton chapelieri and Croton vatomandrensis, we provide IUCN Red List conservation assessments for both species.