-SCLEREIDS: PROPOSAL FOR A NEW CATEGORY OF PALYNOMORPHS LATO SENSU.Palynological analyses of samples from the Upper Cretaceous successions of certain sedimentary basins of southeastern Brazil have revealed the presence of distinctive organic structures attributable to sclereids, which are cells of sclerenchyma (tissue whose principal function is support and protection of vascular plants). In the present study, fossil sclereids have been identified by light microscopy of strew slides prepared for routine palynological analysis. Thirteen basic radially symmetric morphotypes are recognizable, as follows: aculeata, brevis (short, compact), callosa (thickened, callus-like), crenulata, crucis (cross-shaped), elongata, furcata (branched), perforata, rotunda (rounded), simplex (simple, unbranched), spinosa, tenuis (tenuous), and truncata (truncated). All belong to the group of Astrosclereids, which have star-like shapes. Tentatively, the type simplex can be referred to the Gnetophyta and the family Nymphaeaceae; perforata to Loranthaceae; callosa to Magnoliaceae; and furcata to Rutaceae, Oleaceae and Theaceae. These inferred botanical relationships could, in turn, enhance our understanding of the taxonomic composition of the vegetation bordering the studied basins, thus contributing to paleoenvironmental and paleoclimatic interpretations. Moreover, determining the relationship between the astrosclereid morphotypes and the plant organs bearing them could help in the characterization of the terrigenous influx into the basins. The abundance of fossil astrosclereids could also be indicative of paleowildfires. This is implied by the fact that these microfossils are especially abundant in the Santonian strata of the Campos and Santos basins, which incorporate unequivocal evidence of intense conflagration induced by incendiary volcanic activities.Key words: sclereids, astrosclereids, plant anatomy, palynology, Cretaceous, Brazil.RESUMO -Análises palinológicas realizadas em amostras provenientes do Cretáceo Superior de algumas bacias sedimentares do Sudeste Brasileiro revelaram estruturas atribuíveis a esclerócitos, células do esclerênquima, tecido que confere rigidez, sustentação e proteção às plantas vasculares. No presente trabalho, os esclerócitos fósseis foram identificados ao microscópio óptico nas mesmas lâminas das análises palinológicas de rotina. O trabalho preliminar permitiu a identificação de 13 formas (morfotipos) básicas, todas pertencentes ao grupo de astroesclerócitos com formato de estrela: aculeata (aculeado), brevis (compacto), callosa (caloso), crenulata (crenulado), crucis (cruciforme), elongata (elongado), furcata (ramificado), perforata (perfurado), rotunda (arredondada), simplex (simples), spinosa (espinhoso), tenuis (tênue) e truncata (truncado). Inferiu-se o morfotipo simples às gnetófitas e à família Nymphaeacea, o perfurado à Loranthaceae, o caloso à Magnoliaceae e o ramificado às famílias Rutaceae, Oleaceae e Theaceae. O estabelecimento da relação dos morfotipos com suas respectivas planta...