Why do water lilies have astrosclereids

The vascular bundles of the mesophyll are open collateral with bundle sheath rich in chloroplasts Figure 2D - arrow in all evaluated species. In the smaller bundles, the metaxylem Mx has wide vessels interposed by small parenchyma cells Figure 2E in N.

Protoxylem lacunae Pl , delimited by parenchyma cells Pa arranged in regular formation Figure 2E , are present in most large vascular units of the species, except in N. Since leaves do not feature vessel elements, xylem is conducted by tracheids with spiral thickening.

Phloem is well developed, but with reversed arrangement 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. The margin has acute shape in N.

Petiole - The petiole with uniseriate epidermis Ep and hydropoten Hd set along its length Figure 3A occurs in all species. Three layers of sub-epidermal annular collenchyma - Cl - Figure 3B are found in six of the species, except N.

Figure 3- Transverse section of the petiole of Nymphaea. Uniseriate epidermis and angular collenchyma A in N. 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.

Bicollateral bundles Figure 3D occur in six species, except N. There are differences in the number of bundles when comparing the species. Six bicollateral bundles with lacuna As are found in N.

In terms of collateral bundles with lacuna Figure 3F , N. Six collateral bundles without lacuna Figure 3G are present in N. The anatomical differences in the leaves were sufficiently consistent to distinguish the taxa and make it possible to devise an identification key based on the foliar characters easiest to recognise. Leaf blade — All species featured uniseriate epidermis on both surfaces of the leaf blade, a characteristic cited by Adamowicz unpublished results for N. Plant Anatomy. Oxford: Pergamon Press.

Tropical aquatic Plants: morpho-anatomical adaptations. In Del-Claro, K. Encyclopedia of Tropical Biology and Conservation Management. Sistematic Anatomy of the dicotyledons. Oxford: Clarendon Press. The Biology of aquatic vascular plants.

London: Eduard Arnold. This author also observed ample substomatal chambers for the genus, corroborating our data for the species we evaluated. Specialized strutures in the leaf epidermis of Basal Angiosperms: morphology, distribution and homology. American Journal of Botany, vol. That author denominates hydropoten as unicellular or multicellular trichomes and, based on analyses of evolutionary characters, it is affirmed that this trichome is a synapomorphy for Nymphaeales.

Accumulation of heavy metals in epidermal glands of the waterlily Nymphaeaceae. Planta, vol. Non-glandular trichomes observed on the apex of the petiole in N. The dorsiventral anatomy of the blade was observed to have a polygonal arrangement of spongy tissue consisting of typical aerenchyma, and the adaxial region of the mesophyll was occupied by homogeneous palisade parenchyma interrupted by ample substomatal chambers.

As observed in the majority of species we evaluated, the presence of annular collenchymas with cell walls spaced more uniformly, leaving from the circular cell lumen, is corroborated by Sculthorpe's description for Nymphaea. The presence of angular collenchyma in N.

According to Coan et al. A Monograph of the Genus Nymphaea. Washington: Carnegie Institution. However, the completely expanded leaves of Nymphaea evaluated in this study indicate that the cell types observed had already completed ontogenesis and were distributed among the parenchymae, not reaching both surfaces of the leaf.

The type of tubular sclereid described in this work for N. The absence of these structures in N. According to that author, several families of aquatic plants do not form metaxylem, but all evaluated Nymphaea species have metaxylem elements, although the number of cells varies. The occurrence and types of vessels in various organs of the plant in the Monocotyledoneae.

The phyllode theory of the monocotyledonous leaf, with especial reference to anatomical evidence. Annals of botany, vol. Although this characteristic is illustrated in some members of Alismataceae and Pontederiaceae, it has not been cited for Nymphaeaceae. Arber considers that only the occurrence of such bundles outside these midribs, and it, may be considered pseudo-lamina.

So, we believe inverted bundles observed in N. Although the structure is similar in all the species evaluated, the shape of the margin was consistent enough to separate N. The reticulate pattern of the air spaces was observed by Scremin-Dias unpublished results in the petiole of Ludwigia sedoides Humb. Hara and by Bona and Alquini a,b in the petiole of Hydrocleys nymphoides Humb.

Buchenau and Limnobium laevigatum Humb. Heine, indicating that this arrangement is common in the aerenchyma of aquatic plants. With the exception of N. The separate and reduced bundles, with various arrangements among the species of the genus, are cited by Metcalfe and Chalk as being opposite to each another with the xylem facing one another, similar to the pattern observed for the petioles evaluated in our work.

Anatomically, the species described herein feature different taxonomic values, which are consistent for taxa distinction. Plants that were objects of specific studies and which feature only vegetative portions and are morphologically similar may, in light of our study, be separated by anatomical analysis of their leaves.

Abrir menu Brasil. Brazilian Journal of Biology. Abrir menu. Material and Methods 2. Samplings The fully developed leaves leaf blade and petiole of three individuals from different populations of N. Histological preparation Fragments were removed from the margin 1 cm 2 and middle portions of the blade 1 cm 2 and petiole 1 cm , fixed in neutral buffered formalin NBF for 24 h Seago et al.

Analyses and illustrations The analyses and illustrations of materials were carried out using a photonic microscope attached to the image capture and photography system, and the corresponding micrometric scales were displayed.

Results The seven species have several anatomical characters in common; however, we did observe some consistent structures that make it possible to differentiate them Table 1. Table 1- Anatomical characters different obtained for the seven Nymphaea species of the Brazilian Pantanal. Note the similarity to the Nymphaea leaf and the distinct differentiation between regions of mesophyll.

A good example of convergent evolution to similar environmental pressures! Because Nymphaea is aquatic and sits on top of the water, the stomata are located only in the upper epidermis.

You can locate them in the cross section by finding the gaps stomatal pits in the palisade mesophyll. Why wouldn't there be stomata in the lower epidermis? If you see strange branching structures within your Nymphaea leaf cross section, you may be looking at an astrosclereid astro- meaning star.

This is a branching sclerenchyma cell with a thick secondary wall. What function might these cells have? Xerophytes literally "dry plants" are adapted to living in dry conditions with low water availability.

The image below shows the cuticle of the Nerium leaf. Notice how thick it is on the upper adaxial surface of the leaf and how it changes in thickness as it transitions to the lower abaxial surface. In xerophytic leaves, stomata tend to be located on the lower abaxial surface. This side of the leaf is usually cooler, as the upper adaxial surface is facing the sun. In extremely dry conditions, stomata might be further protected from the desiccating outer air by being located in stomatal crypts.

Though pines are not angiosperms, they have xerophytic leaves needles. Note the features this pine needle has in common with the Nerium leaf. Mesophytic Leaves A leaf in "normal" conditions is called mesophytic meso- means middle , meaning it is not particularly adapted for either high or low water conditions. The arrangement of tissues in a mesophytic leaf is as described in Fig. As you look at adaptations to water availability, the arrangement of tissues in the leaf above will serve as the "standard" condition for leaves.

Hydrophytic Leaves Hydrophytes literally "water plants" are adapted to living in aquatic conditions. The organization of tissues in this leaf is described in depth in Fig.

The important point here is to note the similarities between this eudicot leaf and the monocot leaf shown in Fig. The similarities in tissue arrangement are due to convergent evolution to an aquatic lifestyle, as opposed to relatedness. Note the similarity in internal anatomy to the hydrophytic eudicot Nymphaea shown in Fig. The upper epidermis is a thin layer of parenchyma with many stomata. Below each stoma, there is a chamber of air located within the palisade mesophyll this makes them easier to find.

Under the palisade mesophyll is a much larger region of spongy mesophyll than we would find in a mesophytic plant leaf. Most of the space is taken up by large air pockets, making this tissue aerenchyma. The lower epidermis has no stomata. Within the mesophyll, there are spiky, pink-stained astrosclereids that have been caught in strange views during the sectioning process.

Location of Stomata Because Nymphaea is aquatic and sits on top of the water, the stomata are located only in the upper epidermis. In the center of the image, there is an elongated empty space within the palisade mesophyll. At the top of this space, there are two guard cells flanking a closed stoma.