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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. International Association for Plant Taxonomy (IAPT) is collaborating with JSTOR to digitize, preserve and extend access to Taxon. The number of studies dealing with plant invasions is increasing rapidly, but the accumulating body of knowledge has unfortunately also spawned increasing confusion about terminology. Invasions are a global phenomenon and comparison of geographically distant regions and their introduced biota is a crucially important methodological approach for elucidation of the determinants of invasiveness and invasibility. Comparative studies of alien floras provide substantial new insights to our understanding of general patterns of plant invasions. Such studies, using information in previously published floras and checklists, are fundamentally dependent on the quality of the assessment of particular species with respect to their taxonomic identity, time of immigration and invasion status. Three crucial decisions should be made when defining the status of a plant species in a given region: (1) whether the taxon is native or alien to that region (origin status); (2) what is its position in the invasion process, i.e., when was it introduced (residence status); and (3) what is the degree of its naturalization and possible invasion (invasion status). Standard floras differ hugely in their treatmentof non-native species and those with appropriate categorization of alien species according to their status are rather rare. The present paper suggests definitions of terms associated with plant invasions and places these into the context of floras. Recommendations are outlined on how to deal with the issue of plant invasions in standard floras with the aim of contributing to a better understanding between taxonomists and ecologists and allowing more detailed comparative analyses of alien floras of various regions of the world.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. International Association for Plant Taxonomy (IAPT) is collaborating with JSTOR to digitize, preserve and extend access to Taxon. A provisional synopsis of the sections of the genus Croton (Euphorbiaceae) Grady L. Webster1 Summary Webster, G. L.: A provisional synopsis of the sections of the genus Croton (Euphorbiaceae). -Taxon 42: 793-823. 1993. -ISSN 0040-0262. The 19th century classification of Croton by Muller Argoviensis is highly artificial. A revised system that incorporates the sections proposed by Baillon and Grisebach is presented, with a key to the 40 sections recognized. For each section, types and synonymy are indicated, along with a description and list of representative species. Described as new are 2 sections (C. sect. Anadenocroton, sect. Corylocroton) and 3 subsections (C. subsect. Cuneati, subsect. Matourenses, subsect. Sampatik); 2 new sectional names (C. sect. Argyrocroton, sect. Luntia) represent changes in rank.Croton is a large and diverse genus of Euphorbiaceae comprising at least 800 species of the tropics and subtropics. In the most recent general synopsis of the family (Webster, 1994), it is associated in the tribe Crotoneae with the Old World genera Mildbraedia and Fahrenheitia. Croton differs from those genera in having staminate flowers with filaments inflexed in the bud, and pistillate flowers with the petals usually reduced. Furthermore, most species of Croton have a characteristic habit, with terminal thyrses of flowers that have mostly solitary pistillate flowers below and cymules of staminate flowers distally.The present article is a contribution towards a better understanding of phyletic relationships within the genus Croton. In contrast to the other large genera of Euphorbiaceae (e.g., Acalypha, Euphorbia, Phyllanthus), no coherent system of sections has heretofore been available in Croton. The classification of Muller (1866, 1873) was patently artificial (as Muller himself implied in various comments on individual species), and was criticized as such by Bentham (1880). Unfortunately, Pax (1890) accepted Miieller's system, and in the latest general treatment by Pax & Hoffmann (1931) Muller's taxa were retained but inflated in rank (by raising sections to subgenera, etc.). In contrast, Baillon (1858, 1861, 1864) and Grisebach (1859) recognized a considerable number of sections that by and large represent natural groups. These were cited in synonymy by Muller and Bentham, but have never been generally adopted because of the prevailing authority of the Miillerian system. In the 20th century, there have been a number of critical regional studies of 793 TAXON VOLUME 42 described many species and provided valuable discussions of interspecific relat...

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Missouri Botanical Garden Press is collaborating with JSTOR to digitize, preserve and extend access to Annals of the Missouri Botanical Garden. ABSTRACTThe family Euphorbiaceae appears to be monophyletic, despite proposals for segregate families. The Euphorbiaceae display a great variety of growth forms, including at least 17 "models" of Hallk. Anatomical characters particularly useful for classification include wood structure, laticifer type, trichomes, and stomata. Inflorescences are basically dichasial, and pseudanthia have evolved several times. Pollen nuclear number and exine structure provide useful criteria for characterizing genera, tribes, and subfamilies. Structure of the seed coat is characteristic for the family and does not provide evidence for a polyphyletic origin of the family. Pollination is prevailingly entomophilous, and seed dispersal by ants is important in many taxa. Geographic distribution patterns of genera show a concentration of primitive taxa in Africa and Madagascar, although in subfamily Crotonoideae there is evidence of a neotropical center. Disjunctions between Africa and South America are common. Bentham's hypothesis of an Old World origin of the family appears well supported. The basic distribution patterns appear to reflect early (Cretaceous and Paleogene) dispersal across land or narrow water barriers and spectacular but rather trivial instances of long-distance dispersal in the late Tertiary and Pleistocene; Tertiary high-latitude dispersals via the Bering land bridge appear to have been relatively insignificant.The Euphorbiaceae, although one of the largest dicot families and conspicuous throughout the tropics, have been relatively neglected by systematists in the 20th century. While other families such as Compositae, Leguminosae, and Solanaceae have been the subjects of various symposia, the very first international conference with a major focus on Euphorbiaceae was held at Kew in 1986(Jury et al., 1987. The Kew symposium, on the Euphorbiales, was heavily biochemical in orientation and focused to a considerable extent on relationships between the Euphorbiaceae and other families. The present symposium in St. Louis is the first in which the classification of the family and its constituent infrafamilial taxa is the major focus of attention.The history of classification systems for the Euphorbiaceae at the subfamilial and tribal level has been reviewed in the Kew symposium on Euphorbiales (Webster, 1987). In my opinion, the two major milestones in this history were the classifications of Adrien Jussieu (1824), who identified the major series of genera that (after much later revision) correspond roughly to current subfamilies, and Jean Mueller (1...