This study revealed a high diversity of secretory structures, including novel ones, in one of the largest clades of Euphorbiaceae. Our results are promising for investigations on the anatomical and ecophysiological bases of species diversification within Euphorbiaceae.

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Besides being vital tools in taxonomic evaluation, the anatomy of plant secretory structures and the chemical composition of their secretions may contribute to a more thorough understanding of the roles and functions of these secretory structures. Here we used standard techniques for plant anatomy and histochemistry to examine secretory structures on leaves at different stages of development of Prockia crucis, to evaluate the origin and development of the structures, and to identify the disaccharides and monosaccharides in the exudates. Fructose, glucose, and sucrose constituted up to 49.6% of the entire secretion. The glands were confirmed to be extrafloral nectaries (EFNs); this is the first report of their presence in the genus Prockia. These EFNs are globular, sessile glands, with a central concavity occurring on the basal and marginal regions of the leaf. The epidermis surrounding the concavity is secretory, forming a single-layered palisade that strongly reacts with periodic acid-Schiff's reagent (PAS) and xylidine Ponceau, indicators of total polysaccharides and total proteins, respectively, in the exudate. On the basis of the similarity of these glands to the salicoid teeth in Populus and Salix, we suggest that these three taxa are phylogenetically close.

Acta bot. bras. 23(4): 923-928. 2009 Introdução Nas Américas, a família Rubiaceae está representada por 229 gêneros e 5200 espécies (Delprete 1999), dentre elas Psychotria carthagenensis Jacq. com distribuição desde a Costa Rica até a Argentina; no Brasil ocorre do Pará ao Rio Grande do Sul (Delprete et al. 2005).Psychotria carthagenensis é encontrada em ambientes bastante distintos . De acordo com estes autores, no Sul do Brasil, a espécie ocorre desde o nível do mar até 600 m de altitude, em três tipologias vegetacionais distintas: Floresta Ombrófi la Densa, Restinga e Ambiente Reofítico, sendo possível observar grande variação morfológica entre as populações de cada uma dessas regiões. Delprete et al. (2005) mencionam, dentre outras características usadas para identifi cação de P. carthagenensis, a presença de estípulas grandes, obtusas, membranáceas e que são completamente decíduas, estando presentes apenas nos ápices dos ramos. Pereira et al. (2006) também ressaltam que as estípulas apicais, cuja forma é lanceolada, são bem evidentes e representam um caráter taxonômico para a espécie.Estípulas em muitas famílias de dicotiledôneas são estruturas capazes de secretar mucilagens, gomas ou resinas (Lersten 1974). Fahn (1979) relata a existência de estípulas jovens, as quais, em muitos gêneros de Rubiaceae, possuem estruturas secretores de mucilagem denominadas coléteres. Sua secreção protege os primórdios foliares contra a dessecação (Solereder, 1908 Ao longo da história da botânica, raras têm sido as publicações detalhando as características estruturais de estípulas e coléteres. Tais estruturas merecem mais estudos, tanto pela relevância taxonômica e fi logenética para a família Rubiaceae, quanto pela possível importância para o sucesso adaptativo das espécies em seu hábitat.Os Brazil). Apical shoot stipule samples were collected, fi xed, and processed for light and scanning electron microscopy studies. Histochemical tests were made on in vivo material. The bases of stipules are connected and the apices are separate. On the adaxial surface, there are multicellular trichomes and the colleters are found among these. They have a constricted base, pores on the cuticle surface, parenchymatic middle axis surrounded by a layer of palisade-like epidermal cells, in which may have raphides. The colleters secrete a mucilaginous substance that is very important to protect the apical shoot and young leaves.

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Trichomes are key functional traits that protect plants against abiotic stresses, herbivores and pathogens. In addition to their ecological roles, trichomes show high morphological variability in many lineages, providing useful characters for species characterization and taxon delimitation. Here, we focus on trichomes in Croton, a megadiverse genus (c. 1200 spp.) of Euphorbiaceae, in which these structures are ubiquitous and exhibit significant variation in form, location on the plant body, density and function. Owing to their functional and taxonomic relevance and the current need for further standardization of their terminology and classification, we revised previous trichome classifications used in the genus. We also provide new trichome data by expanding taxon sampling and using different methodological approaches in plant anatomy to improve understanding of the structural patterns of the trichome types present in the genus. On the basis of our results and literature review, we propose a new classification for trichomes in Croton based on well-defined parameters; this clarifies existing redundancies, is consistent with anatomical evidence and can be easily updated as new types are revealed in future surveys. This contribution will improve communication among taxonomists and promote more meaningful morphological comparability across systematics studies, including those focusing on morphological evolution and functional traits.

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