ABSTRACT Aquatic herbaceous plants are especially suitable for mapping environmental variability in wetlands, as they respond quickly to environmental gradients and are good indicators of habitat preference. We describe the composition of herbaceous species in two oligotrophic wetland ecosystems, floodplains along black-water rivers (igapó) and wetlands upon hydromorphic sand soils (campinarana) in the Parque Nacional do Jaú and the Reserva de Desenvolvimento Sustentável Uatumã in Central Amazonia, both protected areas. We tested for the potential distribution range (PDR) of the most frequent species of these ecosystems, which are the ones that occurred in at least two of the sampled wetlands, using species distribution models (SDMs). In total, 98 aquatic herbaceous species were recorded, of which 63 occurred in igapós and 44 in campinaranas. Most igapó species had ample PDRs across the Neotropics, while most campinarana species were restricted to the Amazon Basin. These results are congruent with studies that described similar distribution patterns for tree and bird species, which emphasizes a high degree of endemism in Amazonian campinaranas. However, we also found differences in the potential distribution of species between the two protected areas, indicating high environmental variability of oligotrophic ecosystems that deserve further investigation to develop effective measures for their conservation and protection.

O conhecimento da anatomia da folha é crucial para o entendimento da adaptação das plantas ao ambiente. O objetivo deste estudo foi descrever a anatomia da lâmina foliar de 11 espécies lenhosas, frequentes nas savanas do extremo norte da Amazônia, com ênfase na identificação de atributos adaptativos a ecossistemas abertos, sujeitos a forte insolação e déficit hídrico sazonal. Amostras de folhas foram coletadas e processadas segundo técnicas usuais para estudos de anatomia e histoquímica. Bowdichia virgilioides, Byrsonima coccolobifolia, By. crassifolia, By. verbascifolia, Casearia sylvestris, Curatella americana, Erythroxylum suberosum, Himatanthus articulatus, Miconia albicans, Roupala montana e Xylopia aromatica apresentaram caracteres típicos de plantas heliófilas e xerófilas, como cutícula espessa e estômatos predominantes na face abaxial, além de forte investimento em tecido fotossintético. Em oito das onze espécies, o parênquima paliçádico (PP) ocupa 50% ou mais do espaço do mesofilo. Curatella americana, mesofilo isobilateral, e Bo. virgilioides, mesofilo homogêneo, foram as espécies com maior investimento em PP (~80% e 100%, respectivamente). Além disso, destaca-se a presença de hipoderme (Bo. virgilioides e X. aromatica) ou de epiderme estratificada, densos indumentos, idioblastos cristalíferos e extensões da bainha de feixes. Em síntese, este conjunto de atributos estruturais protege a lâmina foliar contra o excesso de luminosidade, aumenta a resistência mecânica, minimiza a transpiração e contribui para manutenção do balanço hídrico da planta, favorecendo, portanto, o estabelecimento destas espécies nas savanas sazonais do norte da Amazônia.

Knowledge of the anatomical characteristics of the leaf blade is crucial to the understanding of plant adaptation to the environment. The objective of this study was to describe the leaf anatomy of 11 woody species of common occurrence in the open savannas of the northern edge of the Amazon. The focus of the study was on the identification of leaf adaptive features to cope with high irradiances and seasonal water deficits. Leaf samples were fixed and processed by the usual methods for anatomical and histochemical studies. Bowdichia virgilioides, Byrsonima coccolobifolia, By. crassifolia, By. verbascifolia, Casearia sylvestris, Curatella americana, Erythroxylum suberosum, Himatanthus articulatus, Miconia albicans, Roupala montana and Xylopia aromatica showed leaf anatomical traits typical of heliophilous and xerophilous plants such as thick cuticle, stomata prevailing on the abaxial surface, strong investment in photosynthetic tissue. In eight of the eleven species the palisade parenchyma (PP) occupied 50% or more of the mesophyll. Curatella americana, with isobilateral mesophyll, and Bo. virgilioides, with homogeneous mesophyll were the species with the highest investment in PP (~80% and 100%, respectively). Leaves were also characterized by the presence of hypodermis (Bo. virgilioides and X. aromatica) or stratified epidermis, dense indumenta, crystalliferous idioblasts and bundle sheath extensions. This distinctive assortment of anatomical traits helps protecting the leaf blade against excessive irradiances, increases mechanical strength, minimize transpiration and contribute to the maintenance of leaf water balance. Overall they favor the establishment of these species in the seasonal savannas of northern Amazon.