The Contribution of Embyrology to the Systematics of the Euphorbiaceae

Abstract

The Euphorbiaceae are often described as a heterogeneous group with ambiguous affinities. Although their vegetative and floral characters are markedly modified in relation to the habitat and pollination mechanisms, the embryological features are comparatively more conservative, and therefore quite useful in the delimitation of as well as in understanding of relationships. The diagnostic embryological characteristics of the family are: (1) tetrasporangiate anther, 4-or 5-layered anther wall, fibrous endothecium, ephemeral middle layer(s), secretory tapetum with multinucleate cells, simultaneous cytokinesis, tetrahedral, decussate and isobilateral microspore tetrads, and 2-or 3-nucleate pollen; (2) tncarpellary, syncarpous, and trilocular ovary with one or two ovules in each locule, axile placentation, anatropous or hemianatropous, bitegmic, crassinucellate ovule, placental obturator and presence of hypostase; (3) embryo sac with ephemeral antipodal cells, nuclear endosperm and mature embryo with broad/leafy cotyledons; and (4) albuminous seed with both integuments forming seed coat, and outer epidermis of inner integument developing into a fibrous or sclerotic layer. Most of the 30 families included in the Euphorbiales by various authors have significant embryological differences from Euphorbiaceae. It appears more appropriate that the Euphorbiales should include only one family, the Euphorbiaceae. The closeness of the Euphorbiales with the Malvales finds support on embryological grounds.The present level of embryological information substantiates the classification of the Euphorbiaceae into five subfamilies. Jt seems that the Acalyphoideae diverged rather early from the Phyllanthoideae-Oldfieldioideae, and later the Crotonoideae and the Euphorbioideae evolved as independent lines from the Acalyphoideae. Since only 16 of the 50 tribes have so far been embryologically explored, comments on the tribal classification must await further probes into their reproductive biology.

Systematic affinities of Rhizophoraceae and Anisophylleaceae, and intergeneric relationships within Rhizophoraceae, based on chloroplast DNA, nuclear ribosomal DNA, and morphology

“…Morphological data-We expanded the genus-level morphological data sets of Juncosa and Tomlinson (1988a), Keating and Randrianasolo (1988), and Tobe and Raven (1988b) to all species in the molecular study (Appendix 3) and added the outgroups Erythroxylaceae (Schulz, 1907;Badre, 1973a, b;Boesewinkel and Geenen, 1980;Verdcourt, 1980;Weberling, Lorcher, and Bohnke, 1980;Rury, 1981;Behnke, 1988) and Drypetes (Levin, 1986;Kapil and Bhatnagar, 1994;Dunlop, Leach, and Cowie, 1995;Tokuoka and Tobe, 1999). Additionally, some characters from published studies were recoded.…”

Floral morphology and anatomy of Dalechampia alata Klotzsch ex Baill. (Euphorbiaceae), with emphasis on secretory structures

“…According to Endress (1994), a zone with lignified cell walls (hypostase) often develops between the end of the vascular bundle and the base of the embryo sac. Although hystochemistry test were not made, these cells in D. alata are very similar to those described for D. stipulaceae (Souza et al, 2010) and other Euphorbiaceae species (Kapil and Bhatnagar, 1994). The hypostase is probably related to the translocation of nutrients into the embryo sac and endosperm (Tilton, 1980) The projection seen at the base of the funiculus was considered as an obturator.…”

“…The hypothesis of nutrition is also suggested as a function of this structure (Souza, 2009). Both the presence of hypostase and the obturator were considered as an embryological characteristic of the family Euphorbiaceae by Kapil and Bhatnagar (1994).…”

Análises Ontogenéticas Em Sementes De Euphorbiaceae

“…Outra característica relevante encontrada em Euphorbiaceae é a projeção do nucelo, que se estende para fora da micrópila (LANDES, 1946;KAPIL;BHATNAGAR, 1994). Estes últimos autores mostraram que essa projeção ocorre em vários gêneros de todas as subfamílias de Euphorbiaceae, e tanto obturador quanto a projeção do nucelo podem estar envolvidos na nutrição do tubo polínico, ou com a função de guia até o saco embrionário.…”

“…Certas características são de fundamental importância no entendimento da família, como a presença do obturador e de projeção do nucelo, assim como a presença da carúncula nas sementes (KAPIL;BHATNAGAR, 1994).…”