Jess A. Peirson

A worldwide molecular phylogeny and classification of the leafy spurges, Euphorbia subgenus Esula (Euphorbiaceae)

The leafy spurges, Euphorbia subg. Esula, make up one of four main lineages in Euphorbia. The subgenus comprises about 480 species, most of which are annual or perennial herbs, but with a small number of dendroid shrubs and nearly leafless, pencil-stemmed succulents as well. The subgenus constitutes the primary northern temperate radiation in Euphorbia. While the subgenus is most diverse from central Asia to the Mediterranean region, members of the group also occur in Africa, in the Indo-Pacific region, and in the New World. We have assembled the largest worldwide sampling of the group to date (273 spp.), representing most of the taxonomic and geographic breadth of the subgenus. We performed phylogenetic analyses of sequence data from the nuclear ribosomal ITS and plastid ndhF regions. Our individual and combined analyses produced well-resolved phylogenies that confirm many of the previously recognized clades and also establish a number of novel groupings and place- ments of previously enigmatic species. Euphorbia subg. Esula has a clear Eurasian center of diversity, and we provide evidence for four independent arrivals to the New World and three separate colonizations of tropical and southern Africa. One of the latter groups further extends to Madagascar and New Zealand, and to more isolated islands such as Reunion and Samoa. Our results confirm that the dendroid shrub and stem-succulent growth forms are derived conditions in E. subg. Esula. Stem- succulents arose twice in the subgenus and dendroid shrubs three times. Based on the molecular phylogeny, we propose a new classification for E. subg. Esula that recognizes 21 sections (four of them newly described and two elevated from subsectional rank), and we place over 95% of the accepted species in the subgenus into this new classification.

Evolutionary bursts in Euphorbia (Euphorbiaceae) are linked with photosynthetic pathway.

The mid‐Cenozoic decline of atmospheric CO2 levels that promoted global climate change was critical to shaping contemporary arid ecosystems. Within angiosperms, two CO2‐concentrating mechanisms (CCMs)—crassulacean acid metabolism (CAM) and C4—evolved from the C3 photosynthetic pathway, enabling more efficient whole‐plant function in such environments. Many angiosperm clades with CCMs are thought to have diversified rapidly due to Miocene aridification, but links between this climate change, CCM evolution, and increased net diversification rates (r) remain to be further understood. Euphorbia (∼2000 species) includes a diversity of CAM‐using stem succulents, plus a single species‐rich C4 subclade. We used ancestral state reconstructions with a dated molecular phylogeny to reveal that CCMs independently evolved 17–22 times in Euphorbia, principally from the Miocene onwards. Analyses assessing among‐lineage variation in r identified eight Euphorbia subclades with significantly increased r, six of which have a close temporal relationship with a lineage‐corresponding CCM origin. Our trait‐dependent diversification analysis indicated that r of Euphorbia CCM lineages is approximately threefold greater than C3 lineages. Overall, these results suggest that CCM evolution in Euphorbia was likely an adaptive strategy that enabled the occupation of increased arid niche space accompanying Miocene expansion of arid ecosystems. These opportunities evidently facilitated recent, replicated bursts of diversification in Euphorbia.

Further Support for the Crotoneae Phylogeny: A New Species of Brasiliocroton (Euphorbiaceae) Based on Morphological, Geographical, and Molecular Evidence

Abstract Brasiliocroton muricatus is a new species from eastern Brazil that is described, illustrated, and placed in a phylogenetic context. It is only the second known species of Brasiliocroton. Its phylogenetic position was inferred based on sequences from the nrITS and plastid trnL-F markers, using a sampling of closely related genera in tribe Crotoneae. Brasiliocroton muricatus was recovered within tribe Crotoneae, forming a clade with B. mamoninha. This clade is in turn sister to the large genus Croton, giving additional support to previous phylogenetic studies including B. mamoninha. The most obvious morphological characters distinguishing the new species from B. mamoninha are the unisexual, axillary inflorescences and the smaller fruits with muricate surface and white, stellate trichomes, as opposed to bisexual, terminal inflorescences and bigger fruits with smooth surface and ochraceous to brown dendritic trichomes in B. mamoninha. Both species of Brasiliocroton have the filaments of the staminate flowers erect in bud, which is the main character state distinguishing them from the closely related Croton and Astraea. Additional morphological features distinguishing Brasiliocroton and Croton from the rest of tribe Crotoneae are also discussed.

THE VASCULAR FLORA OF SAYRES POND, A REMNANT PRAIRIE FEN IN CHAMPAIGN COUNTY, OHIO

Abstract Sayres Pond in Champaign County, Ohio, is a characteristic prairie fen remnant. The site harbors an assemblage of wetland plants that are indicative of their fen habitat and at the same time uncommon in west-central Ohio. Although not as species-rich as some larger remnant fens in the region, floristic diversity at Sayres Pond is quite high considering its small area (approximately 1.6 ha surveyed). A total of 102 species in 40 families and 80 genera were documented from Sayres Pond during this study. The flora has a distinct northern component but shows affinities to wet prairies and marshes of the Midwest and Southeast. Six state-listed rare plant species have been reported from the site since 1970, although only three were observed during this study. Comparison to a previous study indicates that over a 27-year period woody species encroached considerably into the fen meadow. Sixty-five of the 120 species (54%) previously reported from the site were not found during this study. The reasons for this loss are not fully understood, but the transition from open meadow vegetation to closed-canopy shrub carr has likely been a major factor in species loss at Sayres Pond.

A Taxonomic Revision of Collinsonia (Lamiaceae) Based on Phenetic Analyses of Morphological Variation

Abstract Collinsonia (Lamiaceae) is a small genus restricted to eastern North America with four species commonly recognized: C. canadensis, C. serotina, C. tuberosa, and C. verticillata. Considerable taxonomic confusion exists within subgenus Collinsonia (all taxa except C. verticillata). Principal components and canonical variates analysis were performed on a macromorphological dataset of 23 variables scored for 118 specimens of subgenus Collinsonia. Results from field and herbarium observations and from the phenetic analyses indicate that specimens of C. serotina with four stamens (hereafter referred to as C. anisata) represent a distinct species. Specimens of C. serotina with two stamens are intermediate between C. canadensis and C. anisata and are tentatively recognized as C. punctata; further study is needed to determine their origin and evolutionary status. Collinsonia tuberosa and C. canadensis show considerable phenetic overlap and are here merged under C. canadensis. Four species of Collinsonia are now recognized: C. anisata, C. canadensis, C. punctata, and C. verticillata.