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.

O estudo apresenta a descrição anatômica foliar de Barnebya, um gênero endêmico do Brasil com apenas duas espécies. O objetivo deste trabalho foi descrever a anatomia foliar e identificar características diagnosticas para a taxonomia e sistemática deste gênero. Folhas herborizadas das espécies B. dispar (Griseb.) WR Anderson & B. Gates e B. harleyi WR Anderson & B. Gates foram reidratadas e processadas de acordo com os métodos anatômicos usuais para análise em microscopia de luz. Os caracteres anatômicos foliares diagnósticos são: a presença e o número de feixes acessórios no pecíolo, conformação do feixe vascular da nervura central, presença de tricomas, presença de ornamentação na parede externa de células epidérmicas na face abaxial do limbo foliar e os tipos de monocristais. Os resultados obtidos no presente estudo mostraram e ressaltam que caracteres anatômicos relacionados a pecíolos são importantes na caracterização de gêneros e caracteres relacionados a lâminas foliares são importantes na caracterização de espécies em Malpighiaceae, corroborando estudos anteriores e realizando pela primeira vez a descrição anatômica foliar de Barnebya.

Rocky outcrops are known for low humidity, rainfall and high solar radiation, factors that limit the development of some vegetables. However, some species of the genus Anemia occurring in these environments. Thus, understanding the anatomical characters present in these vegetables are important for botanical and biodiversity knowledge in rock fi elds. We described the leaf anatomy of six species of Anemia to identify characters adapted to rocky outcrops for ferns. Herbarium samples were rehydrated. Field-collected leaves, were also sampled, the material was subjected to standard anatomical study by light microscopy, and secretions were evaluated by histochemical of the secondary compounds, with ruthenium red, tannic acid, ferric chloride, lugol, Sudan black B, vanillin/hydrochloric acid, Dragendorff's reagent and ponceau xylidine. Histochemical tests were positive for phenolic compounds, alkaloids, polysaccharides, and proteins in A. buniifolia, A. oblongifolia, A. presliana, and A. trichorhiza. Our fi ndings revealed that several structural and histochemical characters of Anemia with trichomes, conical stegmatas, phenolic compounds, mucilages and alkaloids are related to reducing water loss, providing an adaptive value to species in extreme environments, such as rocky outcrops, in addition to new data relevant to the group taxonomy, such as the presence of amphistomatic leaves in A. trichorhiza.