Recent molecular systematic studies have significantly improved our understanding of the large, complex, and cosmopolitan plant family Rubiaceae, comprising about 13,000 species. Besides the obvious importance of DNA phylogenetic data, cytological studies have long added important basic information on the circumscription of clades and relationships within the family. In light of recent changes affecting a large number of tribes and genera, the current knowledge on the systematics of Neotropical Rubiaceae is reviewed with a focus on Costa Rica, which harbors an exceptionally rich Rubiaceae flora including most of the genera and biogeographic elements present in the Neotropics. Based on this systematic framework, previously published chromosome counts on Costa Rican taxa are reviewed and 49 new chromosome counts are reported. In total, 110 accessions of 75 species or infraspecific taxa representing 36 genera of Costa Rican Rubiaceae are discussed and supplemented by new counts for extraterritorial taxa when appropriate. Altogether the present study includes the first chromosome counts reported for the tribes Cordiereae and Hillieae, as well as for 10 genera and 27 species, providing new aspects of Rubiaceae systematics.

Axonopus P. Beauv. comprises nearly 90, mostly New World, species characterized by having spikelets with the inverse position (i.e., the backs of the upper glume and the upper lemma turned away from the rachis). The genus has been divided into four sections, five series, and three subseries, based exclusively on morphological features. Previous phylogenetic analyses based on a limited sampling of species showed Axonopus to be a monophyletic genus. In this study we increased the number of species sampled (46 species in the combined tree) and sequenced four DNA regions (external transcribed spacer [ETS], internal transcribed spacer [ITS], trnL-F, and ndhF). We tested the monophyly of Axonopus and its traditional infrageneric categories using parsimony, likelihood, and Bayesian inference. Additionally, we performed ancestral character state reconstructions of 45 morphological characters to infer autapomorphies of the species and synapomorphies for the genus and clades. Our findings confirmed Axonopus as a monophyletic genus only when Centrochloa Swallen and Ophiochloa Filg., Davidse & Zuloaga are included within it. Our analyses also showed that, with the exception of section Lappagopsis, infrageneric categories from previous classifications of the genus are artificial. Twenty-one morphological character states were identified as potential autapomorphies; two were reconstructed as potential synapomorphies for Axonopus, whereas 12 were reconstructed as potential synapomorphies for specific clades within the genus. Further molecular analyses, including sequencing of unlinked nuclear genes, are needed in order to reach a robust phylogenetic classification of the genus.

The taxonomic boundaries of Centaurea L. species and infraspecific taxa are often blurred by hybridizations. However, counterbalancing genetic isolation contributes to maintaining taxonomic limits and fostering rapid speciation processes. Radiant (R) and non-radiant (NR) capitula are two major floral morphs present in Centaurea. However, it is unclear how gene flow affects the distribution of floral morphotypes across populations and taxa. We have investigated the taxonomic differentiation and potential effect of genetic isolation in R and NR populations of Iberian Centaurea sects. Jacea (Mill.) Pers. ex Dumort. and Lepteranthus (Neck. ex DC.) Dumort. A total of 510 individuals from 58 populations (12 taxa) were analyzed using 165 amplified fragment length polymorphism (AFLP) markers. Genetic diversity and structure parameters were estimated at the taxon, population, and floral morphotypic levels. We tested whether there was correlation between population pairwise fixation index (Fst) genetic distances and the inbreeding coefficient (Fis), taken as a surrogate of reproductive isolation between the R and NR morphotypes of each group, and also taking into account geographic distances, using distance-based redundancy analysis (dbRDA). We also performed isolation by distance (IBD) tests between different floral morphotypes, aiming to infer the impact of genetic isolation on evolutionary and taxonomic divergence of the individuals. The taxa of Centaurea sects. Jacea and Lepteranthus constitute independent evolutionary lineages. Most of the detected genetic clusters match the taxonomic circumscription proposed in our most recent treatments. Genetic diversity was highest in C. debeauxii Godr. & Gren. subsp. debeauxii and subsp. grandiflora (Gaudin ex Schübl. & G. Martens) Devesa & Arnelas and in C. jacea L. subsp. angustifolia (DC.) Gremli (R) and lowest in C. nevadensis Boiss. & Reut. (NR) within the Centaurea sect. Jacea clade, whereas it was highest in C. linifolia L. within the Centaurea sect. Lepteranthus clade. Population-level dbRDA tests did not detect a significant correlation of R versus NR genetic distances and Fis values in any of the studied cases; by contrast, they detected significant correlation with longitude (C. jacea subsp. angustifolia, C. debeauxii, C. linifolia–C. stuessyi Arnelas, Devesa & E. López) or latitude (C. nigra L.). IBD analysis at the individual level showed that, in addition to geography, other morphotype-related factors may affect the genetic differentiation of R versus NR morphs in C. nigra, C. debeauxii, and C. linifolia–C. stuessyi. These results suggest that the fixation of the different morphs within the same taxon or group may be explained by geographic isolation, though we could not discount other potential unknown factors that could have contributed to microspeciation in these recently divergent populations, which originated only several thousands of years ago.

A comprehensive taxonomic treatment for the New World genus Duranta L. (Duranteae, Verbenaceae) is presented for the first time. The genus consists of shrubs or small trees that are largely distributed in the Neotropics. The analyses of the morphological features support the recognition of 31 Duranta species. Duranta repens L. var. canescens Moldenke and D. mutisii L. f. serrulata Moldenke are elevated to the species rank. The previously misunderstood identity of D. obtusifolia Kunth is here untangled and properly discussed, while D. buxifolia Poir., endemic to the Caribbean, and D. xalapensis Kunth, endemic to Mexico, are resurrected from the synonymy of D. triacantha Juss. and D. erecta L., respectively. Eight taxa are here synonymized: D. brachypoda Tod. (= D. erecta), D. repens var. lopez-palacii Moldenke (= D. canescens P. Moroni), D. repens var. serrata Moldenke (= D. stenostachya Tod.), D. sprucei Briq. var. breviracemosa Moldenke (= D. mutisii), D. arida subsp. serpentina R. W. Sanders & Judd (= D. arida Britton & P. Wilson), D. peruviana var. longipedicellata Moldenke (= D. peruviana Moldenke), D. parvifolia Moldenke (= D. vestita), and D. vestita var. glabrescens Moldenke (= D. vestita Cham.). Duranta cajamarcensis Moldenke and D. parviflora Turcz. are reclassified as belonging to genera Citharexylum L. and Priva Adans., respectively. Lectotypes are designated for the names D. recurvistachys Rusby (second-step), D. rostrata Pasq., and D. xalapensis Kunth. Furthermore, D. penlandii Moldenke is reported for the first time in Colombia.

This examination of Edgar Anderson's career from his undergraduate studies at Michigan Agricultural College beginning in 1914 to his death at the Missouri Botanical Garden in 1969 is an opportunity to trace the study of plants in the middle half of the 20th century. He came to the Missouri Botanical Garden in 1922 as geneticist, but he took Senior Botanist as his last title. His perspective was always generalist and synthetic, applying insights from specialization for their broadest implications. This approach led to his recognition of the role of repeated backcrosses, introgressive hybridization, as a major evolutionary mechanism, a view being tested and explored increasingly by today's workers. Analogously, his disciplinary approach similarly reflected introgression as he helped incorporate genetics, cytology, ecology, and developmental biology—in a word, biosystematics—into the botany that he studied as a young man.