Abstract
The aim of this work was to determine the anatomical adaptations of leaves and stems of four species of Poaceae (Cynodon dactylon L. Pers., Chloris barbata SW. (Chloridoideae), Setaria verticillata L. P. Beauv., and Panicum coloratum L. (Panicoideae)) growing naturally at Al-Ha'ir region near Riyadh, Saudi Arabia. Cross-sections of the leaves revealed that the epidermis cells were spherical to oval and formed one layer with a thick cuticle as well as numerous bulliform cells in a fan shape and prickles. Ground tissue (mesophyll) consists mostly of chlorenchyma cells. A large vascular bundle surrounded by two bundle sheaths, outer sheath parenchyma and inner sheath sclerenchyma were observed in C. barbata and C. dactylon, while one bundle sheath of sclerenchyma surrounds the vascular bundle in S. verticillata and P. coloratum, while one bundle sheath with chlorenchymatous cells surrounded the small vascular bundles. Our results showed that all species contained a Kranz anatomy indicative of a C4 photosynthetic pathway despite belonging to two different subfamilies, Panicoideae and Chloridoideae. Oil droplets appeared in the mesophyll tissue of P. coloratum and S. verticillata. Cross-sections of stems revealed an epidermis which consists of one layer of cells with spherical to oval shape and had a thick cuticle. Ground tissue contains strands of chlorenchyma cells followed by sclerenchyma tissue surrounding vascular bundles, thereby making a continuous cylinder. The vascular bundles were scattered in the ground tissue, with each vascular bundle surrounded by a single sclerenchymatous bundle sheath. Our results indicate that these plants were characterized by anatomical adaptations that enhance drought-tolerance capabilities, facilitating survival in arid and semi-arid regions such as Al-Ha'ir and thus these plants can be used to increase vegetation cover and pasture area in dry environments. Key words: Anatomy, adaptations, Poaceae, Cynodon dactylon, Chloris barbata, Setaria verticillata, Panicum coloratum.
Highlights
Many studies have focused on the anatomical aspects of the Poaceae, such as Shaheen et al (2012), who observed differences in leaf epidermal characteristics among six Panicum spp. native to Pakistan; these included variations in the shape of the phytoliths, prickles, large and small trichomes, and stomata, factors that were often used as important taxonomic indicators at the genus level
Cross-section of the blades of C. dactylon, C. berbata, S. verticillate and P. coloratum leaves showed that the leaves were V-shaped, and the vascular bundles appeared in a single row parallel to the lower and upper surfaces of the leaf
Ground tissue in S. verticillata consists of 2 to 10 layers of irregularly-shaped parenchyma cells with thin cellulose walls free of chloroplasts followed by 2 to 3 layers of chlorenchyma cells filled with chloroplasts (Figure 5a)
Summary
Beauv were part of the Panicoideae subfamily of the Poaceae family These plants were considered permanent herbs, with the exception of S. verticillata, grow wild in Al-Ha'ir, an area south of Riyadh city in Saudi Arabia. Ahmad et al (2011) in a study of leaf epidermal characteristics of five plant species in Pakistan, including C. barbata and C. dactylon, found that differences in stomatal apparatus, subsidiary cells shape, the long epidermal cells, and silica cells were useful for distinguishing among species. Leaves epidermal characteristics of 13 species within 10 genera of Poaceae were studied by Nazir et al (2013) They characterized the plants that grow in coastal zones by the presence of rows of silica bodies, which differed in shape and size among the plant species, silica bodies were cross- or dumb-bell-shaped or intermediate between the two and accompanied by cork cells
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