Grady L. Webster

Alien plants in checklists and floras: towards better communication between taxonomists and ecologists

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 treatment of 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.

Synopsis of the Genera and Suprageneric Taxa of Euphorbiaceae

This revised synopsis of the taxa of Euphorbiaceae recognizes, and provides keys to, 5 subfamilies, 49 tribes, and 317 genera. Two new tribes, Croizatieae and Podocalyceae, are proposed, as well as four new subtribes, Leptopinae, Podocalycinae, Pycnocominae, and Tetracoccinae; five taxa are reduced to subtribal status. One genus (Ophellantha) is reduced to a section; 14 new binomial combinations are proposed. Lectotypifications are provided for almost all taxa not previously typified

Classification of the Euphorbiaceae

The 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 Halle. 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

CONSPECTUS OF A NEW CLASSIFICATION OF THE EUPHORBIACEAE

Summary A new classification of the suprageneric taxa of Euphorbiaceae is presented in outline, including a key to the five subfamilies recognized. Latin descriptions are provided for seven new tribes and ten new subtribes.

Usage and bioassays in Phyllanthus (Euphorbiaceae). IV. Clustering of antiviral uses and other effects

A number of species of the genus Phyllanthus (Euphorbiaceae) have been tested for their efficacy as antivirals, partly on the basis of references to traditional usage for the treatment of diseases possibly having a viral origin. There are also many references to indigenous uses and to laboratory assays for other biological activities in this large genus (550+ species). These citations have been arranged by subgenus, section, subsection and species and have been published in three previous papers. This paper summarizes selected clustering of usage and effect by subgeneric taxa. Consideration of the data from ethnobotany, in vitro assays and clinical trials supported the presence of some type of biological activity(s) particularly within the subgenus Phyllanthus. Although the herbaceous species of subgenus Phyllanthus have been extensively used to treat jaundice, and have generally inhibited hepadnavirus DNAp, effects on chronic infection with hepatitis B virus (HBV) or related viruses have generally been negative. Alternative explanations for the wide usage have been little explored. Other medical categories suggested possible leads for research, or possibly, herbal or galenic remedies with bona fide effects. In most cases, the data remain suggestive but not conclusive.

A provisional synopsis of the sections of the genus Croton (Euphorbiaceae)

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.

Pollination of Two Species of Dalechampia (Euphorbiaceae) in Mexico by Euglossine Bees

The large genus Dalechampia, including over 100 species of great vegetative diversity, has a basically uniform pseudanthial inflorescence. Investigation of two sympatric species in Mexico has shown considerable divergence in pollination adaptations. In D. spathulata, male euglossine bees are attracted by and collect aromatic substances secreted by the extra-floral gland of the inflorescences. In D. magnistipulata, female euglossine bees are attracted by and collect sticky resins secreted by the homologous gland. This study adds a new genus and family to the list of plant taxa exhibiting the male euglossine pollination syndrome which has been so well documented in tropical orchids. It also further elucidates a unique mode of pollinator attraction by resin production which has been reported from only one other plant genus. THE IMPORTANCE OF BEES of the tribe Euglossini in pollinating flowers in the American tropics has been pointed out by a number of workers (Dodson 1966, Janzen 1971, Zucchi et al. 1969). Perhaps most attention has been given to pollination relationships between male euglossine bees and orchids, which involve a number of coevolved adaptations on the part of both plant and insect (Dodson and Frymire 1961, Vogel 1963, Dodson et al. 1969, Dressler 1968, van der Pijl and Dodson 1971). In this paper we are reporting for the first time pollination by euglossine bees of two sympatric species of Dalechampia, a large genus of Euphorbiaceae with more than 100 species of primarily American distribution (Pax and Hoffmann 1919, Webster and Burch 1968). No visits to flowers of Dalechampia by euglossine bees have ever been reported in the literature; in two published accounts, stingless bees (Meliponini) have been reported as floral visitors to Dalechampia scandens L. in Brazil and to D. bidentata Bl. in Java (MMuller 1879, Cammerloher 1931). Both of the reports mention visits by worker bees, which collect resins from the inflorescences of Dalechampia for use in nest-building. The inflorescence structure in Dalechampia is unique in the Euphorbiaceae: the flowers are subtended by two large, often brightly colored, bracts so that the inflorescence as a whole functions as a bilabiate pseudanthium (Michaelis 1924, Venkata Rao 1971, Webster and Webster 1972). Above the insertion of the bracts, there is a cyme of three sessile pistillate flowers and a terminal highly modified pleiochasium of usually 9-12 staminate flowers. Part of the bractlets of the staminate inflorescence are converted into secretory structures, forming en masse a large conspicuous gland which in most species exudes a highly sticky resinous compound (figs. 1, 3). Euglossine bees (tribe Euglossini, family Apidae) are important pollinators in the neotropical region; females collect pollen for brood provisioning, and both male and female bees ingest nectar as the energy source for flight and maintenance. Visits by euglossines for pollen or nectar have been recorded for a large number of plants in the neotropics, including species in the Caesalpiniaceae, Marantaceae, Melastomaceae, Ochnaceae, Solanaceae, Verbenaceae, etc. (Dodson 1966, Zucchi et al. 1969, Janzen 1971, Armbruster pers. obs.). Male euglossine bees also collect volatile compounds, usually from angiosperm inflorescences. The following families contain taxa reported to produce compounds attractive to male euglossine bees: Araceae, Bignoniaceae, Gesneriaceae, Mimosaceae, Myrtaceae, Orchidaceae, and Solanaceae (Dodson 1966, Zucchi et al. 1969, Dressler, pers.

Uses and bioassays in Phyllanthus (Euphorbiaceae): a compilation: II. The subgenus Phyllanthus

References to either indigenous uses or the results of controlled assays are numerous for species of Phyllanthus (Euphorbiaceae). These citations have been arranged by subgenus, section, subsection and species and will be published in four parts, including (Part IV) analysis, discussion and conclusions concerning apparent clustering of some uses or effects within taxa. This paper (Part II) covers the subgenus Phyllanthus.

A New Technique of Preparing Pollen for Scanning Electron Microscopy

AbstractA new technique which avoids the distortion usually present in acetolyzed pollen is outlined. The main steps include hydration in Aerosol-OT, ultrasonication in acetone: water, dehydration in ethanol, transfer to amyl acetate, and critical point drying. Experimental studies, in which pollen treated by the new technique is compared with untreated and with acetolyzed pollen, show much better expansion and more observable detail of exine and colpar structures in the pollen prepared by the new method. Damage to Euphorbiaceous grains, especially those with “crotonoid” ornamentation, is extensive using conventional acetolysis but is circumvented entirely by the critical point drying method. It is concluded that SEM and light microscope studies of pollen should include at least some preparations by a non-acetolytic method such as the present one in order to record an optimal amount of structural information.

Records of usage or assays in Phyllanthus (Euphorbiaceae) I. Subgenera Isocladus, Kirganelia, Cicca and Emblica

References to either indigenous uses or the results of controlled assays are numerous for species of Phyllanthus (Euphorbiaceae). These citations have been arranged by subgenus, section, subsection and species and will be published as three separate papers, followed by a paper discussing the apparent clustering of some uses or effects within taxa. This paper, the first of the series, covers the subgenera Isocladus, Kirganelia, Cicca and Emblica.