RESUMO
BACKGROUND: Flowers in Eriocaulaceae, a monocot family that is highly diversified in Brazil, are generally trimerous, but dimerous flowers occur in Paepalanthus and a few other genera. The floral merism in an evolutionary context, however, is unclear. Paepalanthus encompasses significant morphological variation leading to a still unresolved infrageneric classification. Ontogenetic comparative studies of infrageneric groups in Paepalanthus and in Eriocaulaceae are lacking, albeit necessary to establish evolution of characters such as floral merism and their role as putative synapomorphies. METHODS: We studied the floral development and vascularization of eight species of Paepalanthus that belong to distinct clades in which dimery occurs, using light and scanning electron microscopies. RESULTS: Floral ontogeny in dimerous Paepalanthus shows lateral sepals emerging simultaneously and late-developing petals. The outer whorl of stamens is absent in all flowers examined here. The inner whorl of stamens becomes functional in staminate flowers and is reduced to staminodes in the pistillate ones. In pistillate flowers, vascular bundles reach the staminodes. Ovary vascularization shows ventral bundles in a commissural position reaching the synascidiate portion of the carpels. Three gynoecial patterns are described for the studied species: (1) gynoecium with a short style, two nectariferous branches and two long stigmatic branches, in most species; (2) gynoecium with a long style, two nectariferous branches and two short stigmatic branches, in P. echinoides; and (3) gynoecium with long style, absent nectariferous branches and two short stigmatic branches, in P. scleranthus. DISCUSSION: Floral development of the studied species corroborates the hypothesis that the sepals of dimerous flowers of Paepalanthus correspond to the lateral sepals of trimerous flowers. The position and vascularization of floral parts also show that, during dimery evolution in Paepalanthus, a flower sector comprising the adaxial median sepal, a lateral petal, a lateral stamen and the adaxial median carpel was lost. In the staminate flower, the outer whorl of staminodes, previously reported by different authors, is correctly described as the apical portion of the petals and the pistillodes are reinterpreted as carpellodes. The occurrence of fused stigmatic branches and protected nectariferous carpellodes substantiates a close relationship between P. sect. Conodiscus and P. subg. Thelxinoë. Free stigmatic branches and exposed carpellodes substantiate a close relationship between P. sect. Diphyomene, P. sect. Eriocaulopsis and P. ser. Dimeri. Furthermore, the loss of nectariferous branches may have occurred later than the fusion of stigmatic branches in the clade that groups P. subg. Thelxinoë and P. sect. Conodiscus.
RESUMO
Mapania belongs to Mapanioideae, a quite controversial subfamily in Cyperaceae due to the existence of unusual characters in both reproductive and vegetative organs. The genus is represented by seven species in Northern Brazil but taxonomic valuable information related to the leaf organs is still unknown. The present study aimed the anatomical description of the leaf organs (either basal leaves or cataphylls and involucral bracts) of three representative Brazilian species of Mapania. Samples of cataphylls, basal leaves and involucral bracts were sectioned and stained for observations under light microscopy. The involucral bracts provide the most elucidative characters (ten) to distinguish the three species The basal leaves provides six distinguishing characters and are useful to M. macrophylla and M. pycnostachya, as they are absent in M. sylvatica. Mesophyll arrangement in the involucral bracts supports the circumscription of M. macrophylla and M. pycnostachya in M. sect. Pycnocephala and of M. sylvatica in M. sect. Mapania. Some features as thin-walled epidermal cells, stomata level and aerenchyma were considered to be adaptive to the humid environment in which the species occur. The translucent cells are here considered as aerenchyma precursors and a supportive function is assumed for the bulliform cells on the basal leaves and involucral bracts. No silica bodies were found which confirm it as a diagnostic character of Mapania among Hypolytreae genera.
Mapania pertence à subfamília Mapanioideae que apresenta caracteres incomuns às demais Cyperaceae, tanto vegetativos como reprodutivos. O gênero é representado por sete espécies no norte do Brasil e apresenta ainda lacunas de informações especialmente relacionadas aos órgãos foliares. O presente estudo objetivou a descrição anatômica dos órgãos foliares (folhas basais, ou catafilos, e brácteas involucrais) de três espécies representativas de Mapania no território brasileiro. Amostras de catafilos, folhas basais e brácteas involucrais foram seccionadas e coradas para observações em microscopia de luz. As brácteas involucrais foram as mais elucidativas na separação das espécies, com dez caracteres variáveis, uma vez que ocorrem em todas as espécies durante o estágio reprodutivo. As folhas basais forneceram seis caracteres úteis na distinção de M. macrophylla e M. pycnostachya, já que não ocorrem em M. sylvatica. seguidas das folhas basais. O arranjo do mesofilo das brácteas involucrais suporta a circunscrição de M. macrophylla e M. pycnostachya em M. sect. Pycnocephala e de M. sylvatica em M. sect. Mapania. Características adaptativas ao ambiente úmido também foram encontradas, como epiderme com paredes delgadas, níveis dos estômatos e presença de aerênquima. As células translúcidas do mesofilo foram descritas como precursoras de aerênquima e considerou-se que as células buliformes presentes nas folhas e brácteas involucrais apresentam função de suporte desses órgãos. Corpos silicosos não foram encontrados sustentando o seu uso na delimitação de Mapania e dos demais gêneros de Hypolytreae.
