oxypetala, and elongated sclereids (arrows) traversing the palisade parenchyma (Figure 2B) occur in N.
The blade margin is patterned similarly for all evaluated species, with a layer of regular parenchyma (Rp), without supporting tissue, the absence of palisade parenchyma (Pp), and the presence of sclereids (S), vascular bundle (Vb), stomata and hydropoten (Hd).
For all seven species, there is a similarity in the anatomical pattern of the midrib mesophyll formed by a parenchymal cortex with vascular bundles arranged in regular formation, with the region inside the cortex consisting of regular aerenchyma (As) with sclereids (S--arrows) projected on the inside of the lacunae (Figure 3C).
The large amount of sclereids inside the lacunae offers resistance, as these species do not have supporting tissues (Sculthorpe, 1967).
Sculthorpe (1967) also describes star-shaped sclereids that project into the lacunae of the spongy tissue in members of the family Nymphaeaceae.
Elongated sclereids found in the mesophyll of some species, according to Evert (2006), consist of immature cells; upon the development of the organ, they will reach both surfaces of the epidermis.