The intention of the present wok is to provide an account on the pollen morphological features of Lamiaceae in Saudi Arabia as a basis for future studies of Lamiaceae pollens in the region. Pollen morphology of 20 species belong to 16 genera of the Lamiaceae has been investigated using Light Microscope (LM) and Scanning Electron Microscope (SEM). The study revealed that the pollen grains were characterized by 3-zonocolpate or 6-zonocolpate. Size of the pollen is variable between the genera but not among the species of the same genus. The surface pattern of the exine varies from fine reticulate, rough reticulate, mega-reticulate, reticulate-perforate, bireticulate-perforate or granulate, leading to 6 types of pollen grains. These variations revealed by this study implies that pollen Morphology may be of significant value sharing in solving problems in the classification of Lamiaceae members. A Key to the species, based on the morphological features of pollen grains, is also provided.

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Crystals in 16 species of poisonous plants growing naturally in Saudi Arabia were studied with light microscopy. Three types of crystals were observed: druses, prismatics, and crystal sand. Raphides and styloids were not observed in any of the species studied. Druses occur more frequently in the leaf midrib and in the cortex and pith of the stem. In contrast, crystal sand and prismatic crystals are rare and occur in the leaf, intercostal lamina, and in the vascular tissues. The preliminary results show the absence of the three types of calcium oxalate crystals in the stem and leaf of seven species: Ammi majus L., Anagallis arvensis L., Calotropis procera Ait., Citrullus colocynthis (L.) Schard, Euphorbia peplis L., Hyoscyamus muticus L., and Solarium nigrum L., and the presence of druses, prismatic crystals, and crystal sand either in the leaf and stem or in the leaves or stems of nine species: Anabasis articulata (Forssk.) Moq. in DC., Chenopodium album L., Convolvulus arvensis L., Datura stramonium L., Nerium oleander L., Ricinus communis L., Rumex nervosus Vahl., Pergularia tomentosa L., and Withania somnifera (L.) Dun. in DC. These observations indicate that there is no apparent relationship between the distribution of calcium oxalate crystals and the toxic organs of the plants, and supports the view that the presence of calcium oxalate crystals may not be related to plant toxicity.

Pollen micromorphological characters such as pollen size, shape, number of associated monads, colpi and ornamentation of the tectum surface, of seven species of Acacia belonging to the family Mimosaceae were studied, using light microscope (LM) and scanning electron microscope (SEM). The study showed that the pollen size range from 42.1 to 69.4 µm, pollen shape is round to semi-round, the number of associated monads is 16 or 32, and the colpus is Y-H shaped. The tectum surface ornamentation among the species is variable, it is foveolate in Acacia ehrenbergiana; psilate-foveolate in Acacia nilotica, Acacia laeta and Acacia negrii; and micro-reticulate in Acacia farnesiana, Acacia oerfota and Acacia tortilis ssp. raddiana. An artificial key based on micromorphological characters is provided.

Two concentrations (10-5M and 10-3M) of both GA3 and 2,4-D were used as foliar spray to evaluate the response of date palm (Phoenix dactylifera L.) cv. Khedri seedlings. They affected some of the anatomical characteristics of the first leaf emerging after the beginning of the spray. The high concentration of GA3 increased the size of the midrib and its vascular bundle numbers. Both low and high concentrations of 2,4-D inhibited the formation of the midrib. 2,4-D in both low and high concentrations decreased the number of vessels in both protoxylem and metaxylem and also decreased their diameters, where as GA3 in low and high concentrations have less effect on the number of vessels and its diameters. GA3 in high concentration increased the number of vascular bundles in 1mm long of the leaf blade, while 2,4-D in low and high concentrations decreased their numbers. 10-3M of 2,4-D increased the size and layers of special hypodermal cells.

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. Crosssections 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.

Epidermal characters provide additional features in the assessment of taxonomic relationships among the European species of Antirrhinum. Much of this study confirms the classification derived by Webb but important differences have been observed, viz. A. mollissimum may be considered as identical to A. molle whilst A. boissieri, A. ambiguum and A. rupestre may be assigned as distinct species. Evidence from epidermal characters supports Rothmaler's view that A. majus spp. litigiosum is a subspecies of A. majus and should not be amalgamated with A. barrelieri as proposed by Webb. A. × huteri is proposed to be a hybrid between A. hispanicum and A. boissieri. Thus it is proposed that the section Antirrhinum comprises 20 species with A. majus divided into five subspecies.

The pollen morphological characters of 6 species belonging to 4 genera of the subfamily Stachyoideae (Lamiaceae) growing naturally in Saudi Arabia were investigated with the aid of light microscope (LM) and scanning electron microscope (SEM), to find new features that might increase knowledge of pollen morphology of the species, and also to help the taxonomic characterization of the Stachyoideae genera. The morphological characters studied were size, shape, tectum surface ornamentation, number and type of the colpi. The study indicated that the average size of the pollen was different among the species since the smallest size was that of Nepeta deflersiana (P = 25.2 ± 2 and E = 15 ± 3) while the largest size was that of Salvia aegyptiaca (P =36.5 ± 2 and E = 30.3 ± 2). Pollen shape is spheroidal to sub-spheroidal or prolate. The fine structure of the exine of pollen was slightly different among investigated species. The number and type of colpi of the pollen in species studied were 6-zonocolpate type except those of N. deflersiana and Otostegia fruticosa ssp. schimperi having 3-zonocolpate.