Euphorbieae

Abstract: We present a detailed comparative ontogenetic analysis of pseudanthia of representatives of all three subtribes of Euphorbieae (Euphorbiinae, Neoguillauminiinae, Anthosteminae) in order to clarify their homologies and interpretation. The cyathium of Euphorbia and its allies (subtribe Euphorbiinae) closely resembles a bisexual flower but is traditionally interpreted as an inflorescence bearing clusters of highly reduced male flowers surrounding a single terminal female flower. Previously unreported characters are (1) male flowers formed one above the other in the male inflorescences of some Euphorbiinae, (2) late-developing perianthlike structures in some male flowers of Neoguillauminia cleopatra, (3) evidence for a bracteate origin of the female perianth in Anthosteminae and Neoguillauminiinae, and (4) spatiotemporally independent formation of abscission zone and perianth. Indistinct boundaries between inflorescence, flower, and floral organs demonstrate that defining the cyathium neither as an inflorescence nor as a flower is entirely satisfactory and indicate a "hybrid" flower/inflorescence nature of the cyathium. Based on our current knowledge and the existing phylogenetic context, it is most parsimonious to suggest that the cyathium evolved from a determinate thyrse with a terminal female flower surrounded by dichasial male partial inflorescences. We speculate that the cyathium was formed because of strong condensation and possible overlap between expression zones of regulatory genes.

Abstract: A short history of the tribal arrangement in the vast family Euphorbiaceae has been given by Henri Baillon in France, Jean Muller of Argau in Switzerland, George Bentham in England, and Ferdinand Pax in Germany. Speculation follows on the ancestors of the group, considered to be polyphyletic and probably derived from more primitive orders with hypogynous flowers, such as Tiliales and Malvales, Celastrales, and Rhamnales, all of which are fundamentally woody, as are most of the Euphorbiaceae. Considered to be ancient characters are the presence of petals, the lack of a disk, the retention of a vestigial ovary in the male flowers, numerous stamens, and the imbrication of the sepals. The sequence of the tribes is based on these assumptions, culminating in the most advanced, such as HUREAE, DALECHAMPIEAE, PEREAE, RIcINEAE, CROTONEAE, JOANNESIEAE, ending with the most advanced of all, the EUPHORBIEAE. A dichotomous key to the tribes and their descriptions is provided, usually listing only the principal genera with the approximate number of species (in parentheses). A more detailed account will be published in the author's third volume of The Genera of Flowering Plants. Twenty of the tribes are illustrated by drawings by the author of representative genera. IN A MASTERLY ESSAY entitled "Notes on Euphorbiaceae" read before the Linnean Society of London in 1878,3 George Bentham made the following statement: "Two men, indeed, both of high standing in the science, and with comparatively ample materials at their command, have recently worked up the order with great care and attention independently of each other, and I would readily have followed the lead of either of them, but that the two have so frequently come to conclusions diametrically opposed to each other, that I have been compelled to steer a course of my own through a labyrinth of tribes, subtribes, genera, sections, or vaguely indicated affinities." The two botanists were Henri Baillon in Paris and Jean MViller of Argau in Switzerland, the latter at the time in charge of de Candolle's herbarium in Geneva. After discussing the different results of these two botanists, Bentham continued: "As for myself, in preparing the arrangement for our Genera Plantarum, I have endeavoured to follow the lead of one or other of my predecessors, or of both when they appeared to be not too much opposed to natural affinities; but I have thought it right to take nothing for granted, and to examine for myself every genus, section, or apparently aberrant species of which specimens were available, reconciling as far as was in my power absolute characters with other evidence of natural consanguinity." As space is limited, I need only quote Bentham's judgment of Baillon's contribution: "This he I Received for publication 5 February 1969. 2 Present address: 4 Cumberland Close, St. Margaret's, Twickenham, England. I J. Linn. Soc. Bot. 17: 185-267 (1878). published in 1858 under the title of 'Etude generale du groupe des Euphorbiacees.' This work showed a great deal of careful research and accurate observation; but its practical utility was much marred by a want of method. It contains no well-defined tribes, nor, indeed, any divisions, except twelve series (of which no characters are given), and no conspectus or short diagnoses of the genera to save the need of successively reading through on every occasion a number of detailed descriptions before you could determine a plant sufficiently to study it .... On the other hand, the plates illustrating some of the most important characters of each genus are most useful, the analysis very accurate and well designed, the execution of the figures all that could be desired." Later Baillon gave a more popular account of the family in the fifth volume of his Histoire des Plantes (1874), with magnificent illustrations by M. Faguet, a few of whose dissections I have used in the drawings accompanying this paper. In this work Baillon recognized only 150 genera, including Daphniphyllum (Daphniphyllaceae), Callitriche (Callitrichaceae), and Dichapetalaceae. In his famous Prodromus4 de Candolle was fortunate to obtain the services of Edmond Boissier for the suborder Euphorbieae. Boissier divided this group into two tribes, I. EUPHORBIEAE, the male flowers without a calyx ("calyculus"), and II. ANTHOSTEMEAE, the male flowers with a distinct calyx. The remainder of the family was contributed by Jean Muiller of Argau, Switzerland (usually abbreviated to Muell.-Arg. to distinguish him from 4 de Candolle, Prodromus 15, 2: 1 (1862).

Abstract: A B S T R A C T The circumtropical but preponderantly American genus Dalechampia, comprising nearly 100 species of twining vines (or rarely subshrubs), is strikingly isolated within the Euphorbiaceae because of its distinctive bibracteate inflorescences. There has been considerable taxonomic controversy with regard to the relationships of the genus, and it has been suggested that Dalechampia is allied to the tribe Euphorbieae because of a supposed analogy between its inflorescence and the cyathium in the Euphorbieae. Field and laboratory investigations of the common American species D. scandens, together with a comparative survey of related species, have thrown some light on these problems. The Dalechampia inflorescence seems best interpreted as consisting of a terminal staminate pleiochasium (with part of the lateral branches transformed for nectar production), juxtaposed to a 3-flowered pistillate cyme. The lips of the conspicuous bilabiate involucre are formed by the hypertrophied bracts which subtend the staminate and pistillate cymes. The bisexual inflorescences appear to be distinctly proterogynous, rather than proterandrous, as has been previously suggested. The configuration of the inflorescence-a bilaterally symmetrical pseudanthium-suggests adaptation for crosspollination, but the closing movement of the bracts makes self-pollination probable in the absence of visits by pollinators. The similarity of the Dalechampia inflorescence to the cyathium of the Euphorbieae appears to be entirely superficial, and both reproductive and vegetative data suggest that Dalechampia is related to taxa of tribe Plukenetieae.

Abstract: Phylogenetic relationships within Euphorbiinae were inferred from our analysis of the 3′; end of the chloroplast gene ndhF. A sampling of that subtribe covered 88 species; 3 closely related species from the subtribes Anthosteminae and Neoguillauminiinae and the tiribe Hippomaneae were included as outgroups. A phylogenetic assessment was carried out using the parsimony approach. The relationships revealed via these ndhF data supported the monophyly of subg.Esula, subg.Chamaesyce, subg.Euphorbia, and subg.Lacanthis. However, the polyphyly of subg.Agaloma, subg.Lyciopsis, and subg.Eremophyton also was strongly suggested. The African succulent Euphorbiinae can be divided into primarily two independent groups: 1) spiny succulents, which form a strongly supported clade with three subclades (subg.Euphorbia, subg.Lacanthis, andMonadenium+Synadenium); and 2) non-spiny succulents, which consist of sect.Meleuphorbia, sect.Medusae, sect.Anthacantha, sect.Trichadenia, sect.Pseudeuphorbium, sect.Treisia, and sect.Pseudacalypha. In the ndhF tree, the subg.Esula clade is placed as a sister to the rest of the Euphorbiinae. Thus, the origin of theEuphorbia s.I. should be sought within the herbaceous species of subg.Esula. The core North American endemicEuphorbia groups --Agaloma, Chamaesyce, andPoinsettia — are monophyletic and independent of the South American subg.Agaloma. Instead, they are derived from the AfricanEuphorbia subg.Lyciopsis andEremophyton. The Eurasian subg.Esula clade forms two subclades, which are concordant to sect.Esula and sect.Tithymalus.