Benjamin W. van Ee

Phylogeny, adaptive radiation, and historical biogeography in Bromeliaceae: Insights from an eight-locus plastid phylogeny

PREMISE Bromeliaceae form a large, ecologically diverse family of angiosperms native to the New World. We use a bromeliad phylogeny based on eight plastid regions to analyze relationships within the family, test a new, eight-subfamily classification, infer the chronology of bromeliad evolution and invasion of different regions, and provide the basis for future analyses of trait evolution and rates of diversification. METHODS We employed maximum-parsimony, maximum-likelihood, and Bayesian approaches to analyze 9341 aligned bases for four outgroups and 90 bromeliad species representing 46 of 58 described genera. We calibrate the resulting phylogeny against time using penalized likelihood applied to a monocot-wide tree based on plastid ndhF sequences and use it to analyze patterns of geographic spread using parsimony, Bayesian inference, and the program S-DIVA. RESULTS Bromeliad subfamilies are related to each other as follows: (Brocchinioideae, (Lindmanioideae, (Tillandsioideae, (Hechtioideae, (Navioideae, (Pitcairnioideae, (Puyoideae, Bromelioideae))))))). Bromeliads arose in the Guayana Shield ca. 100 million years ago (Ma), spread centrifugally in the New World beginning ca. 16-13 Ma, and dispersed to West Africa ca. 9.3 Ma. Modern lineages began to diverge from each other roughly 19 Ma. CONCLUSIONS Nearly two-thirds of extant bromeliads belong to two large radiations: the core tillandsioids, originating in the Andes ca. 14.2 Ma, and the Brazilian Shield bromelioids, originating in the Serro do Mar and adjacent regions ca. 9.1 Ma.

Phylogenetics and the evolution of major structural characters in the giant genus Euphorbia L. (Euphorbiaceae)

Euphorbia is among the largest genera of angiosperms, with about 2000 species that are renowned for their remarkably diverse growth forms. To clarify phylogenetic relationships in the genus, we used maximum likelihood, bayesian, and parsimony analyses of DNA sequence data from 10 markers representing all three plant genomes, averaging more than 16kbp for each accession. Taxon sampling included 176 representatives from Euphorbioideae (including 161 of Euphorbia). Analyses of these data robustly resolve a backbone topology of four major, subgeneric clades--Esula, Rhizanthium, Euphorbia, and Chamaesyce--that are successively sister lineages. Ancestral state reconstructions of six reproductive and growth form characters indicate that the earliest Euphorbia species were likely woody, non-succulent plants with helically arranged leaves and 5-glanded cyathia in terminal inflorescences. The highly modified growth forms and reproductive features in Euphorbia have independent origins within the subgeneric clades. Examples of extreme parallelism in trait evolution include at least 14 origins of xeromorphic growth forms and at least 13 origins of seed caruncles. The evolution of growth form and inflorescence position are significantly correlated, and a pathway of evolutionary transitions is supported that has implications for the evolution of Euphorbia xerophytes of large stature. Such xerophytes total more than 400 species and are dominants of vegetation types throughout much of arid Africa and Madagascar.

Molecular Phylogenetics of the Dragon’s Blood Croton Section Cyclostigma (Euphorbiaceae): A Polyphyletic Assemblage Unraveled

Abstract The phylogenetic relationships of Croton section Cyclostigma sensu Webster were examined using nuclear ribosomal ITS and plastid spacer trnL-F sequences from 48 of the 63 species in the group, including members of the four recognized subsections and representing the groups full morphological and geographic range. The two gene phylogenies concurred that section Cyclostigma sensu Webster is polyphyletic, with its members appearing in nine different clades throughout Croton. The clade that retains the taxonomic type of the section and about half of the species sampled is redefined here as a reduced, monophyletic section Cyclostigma, and the remaining species are placed in other sections or informal clades. The ITS and chloroplast phylogenies are discordant regarding the position of the redefined section Cyclostigma suggesting that reticulate evolution might have played a role in the evolutionary history of this group. These results highlight that the tree habit has evolved on multiple occasions in Croton, and that there are other morphological characters that can effectively distinguish different tree lineages in the genus.

Molecular phylogenetics and character evolution of the “sacaca” clade: Novel relationships of Croton section Cleodora (Euphorbiaceae)

Phylogenetic relationships of Croton section Cleodora (Klotzsch) Baill. were evaluated using the nuclear ribosomal ITS and the chloroplast trnL-F and trnH-psbA regions. Our results show a strongly supported clade containing most previously recognized section Cleodora species, plus some other species morphologically similar to them. Two morphological synapomorphies that support section Cleodora as a clade include pistillate flowers in which the sepals overlap to some degree, and styles that are connate at the base to varying degrees. The evolution of vegetative and floral characters that have previously been relied on for taxonomic decisions within this group are evaluated in light of the phylogenetic hypotheses. Within section Cleodora there are two well-supported clades, which are proposed here as subsections (subsection Sphaerogyni and subsection Spruceani). The resulting phylogenetic hypothesis identifies the closest relatives of the medicinally important and essential oil-rich Croton cajucara Benth. as candidates for future screening in phytochemical and pharmacological studies.

A Phylogenetic and Taxonomic Review of Croton (Euphorbiaceae s.s.) on Jamaica Including the Description of Croton jamaicensis, a New Species of Section Eluteria

Abstract The greater Caribbean region has played an important role in the early diversification of Croton L. (Euphorbiaceae s.s.). Jamaica is also important to Croton taxonomy because several of the earliest described species were based on material from the island. The Jamaican species of Croton are found in five distinct clades indicating that there were at least five separate over-water dispersal events of the genus to the island. Croton jamaicensis (section Eluteria Griseb.), a new species endemic to limestone hills along the southern coast of Jamaica, is described and illustrated. The species is phylogenetically most closely related to C. laurinas Sw. and C. grisebachianus Müll. Arg., both also endemic to Jamaica. Several lectotypifications and novel synonymies are required to clarify the taxonomy of the species of Croton that have been described from Jamaica, some of which are widespread in the region.

Taxonomy and Phylogeny of Croton Section Heptallon (Euphorbiaceae)

Abstract A taxonomic key, synonymy, and a molecular phylogeny of the nine species and three varieties of Croton section Heptallon (Euphorbiaceae) are presented. Section Angelandra is synonymized with section Heptallon, and the species from outside of North America that had been placed into these two sections are shown to belong in other clades within the genus. As circumscribed here, section Heptallon is a well-supported clade of annual herbs and subshrubs that ranges from central Mexico to the eastern United States. A new combination, Croton heptalon, is made. Lectotypes are designated for C. corymbulosus, C. elliottii, C. ellipticus, C. engelmannii var. albinoides, C. eutrigynus, C. heptalon, C. leucophyllus var. trisepalis, and Heptallon graveolens. Resumen Una clave taxonómica, sinonimia, y una filogenia molecular son presentados para las nueve especies y tres variedades de Croton sección Heptallon (Euphorbiaceae). Sección Angelandra se sinonimiza con sección Heptallon, y se demuestra que las especies de fuera de Norte América que habían sido incluidas en estas dos secciones pertenecen a otros clados dentro del género. Como está circunscrita aquí, sección Heptallon es un clado con buen apoyo de hierbas anuales y subarbustos que se distribuye desde el centro de México hasta el oriente de los Estados Unidos. Se hace una nueva combinación, Croton heptalon. Se designan lectotipos para C. corymbulosus, C. elliottii, C. ellipticus, C. engelmannii var. albinoides, C. eutrigynus, C. heptalon, C. leucophyllus var. trisepalis, y Heptallon graveolens.

Croton Section Pedicellati (Euphorbiaceae), a Novel New World Group, and a New Subsectional Classification of Croton Section Lamprocroton

Abstract Croton section Pedicellati is described, with a disjunct distribution in Mexico and South America. It is recovered sister to Croton section Lamprocroton in Bayesian, Maximum Likelihood, and Maximum Parsimony analyses of nuclear ITS and chloroplast trnL-F DNA sequence data. Two new subsections, Croton subsection Lamprocroton and Croton subsection Argentini, are recognized within Croton section Lamprocroton. These well-supported sister clades include species with bifid and multifid styles, respectively. Croton breedlovei, a new lepidote species of section Pedicellati, endemic to Chiapas, Mexico, is described. Croton breedlovei is morphologically and phylogenetically closer to other lepidote species from Brazil than it is to the stellate C. tenuilobus, also from Mexico. This suggests two separate dispersal events from South America for the two Mexican species in the section. The replacement names C. longicolumellus and C. tenuicaulis are made for the later homonyms C. microcarpus and C. microstachys. Lectotypes are designated for C. andinus, C. angustifrons, C. burchellii, C. catinganus, C. cerino-dentatus, C. cerino-dentatus var. martii, C. cerino-dentatus var. warmingii, C. cuyabensis, C. eriocladoides, C. linearifolius, C. microcarpus, C. microstachys, and C. saxosus.

An Assessment of the Varieties of Croton glandulosus (Euphorbiaceae) in the United States

Abstract. Croton glandulosus is one of the most common and widespread species of the genus. It is a morphologically variable species for which more than thirty varieties have been described. This work provides a critical evaluation of the varieties of C. glandulosus that have been applied to specimens from North America north of Mexico. Five natively occurring varieties are recognized in this region. Several varieties are reduced to synonymy, and the new combination C. glandulosus var. arenicola is made. Lectotypes are designated for those varieties lacking a designated holotype.

The Circumscription of Croton Section Crotonopsis (Euphorbiaceae), A North American Endemic

Abstract. Croton section Crotonopsis is very distinctive within the genus. It is one of the few groups of the genus that are endemic to the United States. Although the precise phylogenetic relationships of section Crotonopsis have not been established in molecular studies, it is clearly nested within Croton. We hypothesize that it may form a clade with some of the other sections found in North America that have lepidote trichomes and multifid styles. The two species that have been recognized in the section are very similar morphologically; we therefore propose that these two taxa should be included as varieties of a single species and formalize the varietal names, which are Croton michauxii var. michauxii and the new combination C. michauxii var. elliptica. A key to distinguish the two varieties is presented.