A key to the grasses (Poaceae) of Egypt

. A key for identifying 284 native and naturalized Egyptian grass species belonging to 103 genera in 22 tribes and 7 subfamilies is presented. The key is princi-pally based on floral characters of the inflorescence and spikelet. A list and classification of all known species of Egyptian grasses is provided.


INTRODUCTION
The Poaceae (Gramineae) is a large cosmopolitan family with 768 genera and 11,506 species (Soreng et al. 2017). The family includes cereal grasses, bamboos, and species occurring in natural grasslands, cultivated lawns, and pastures. The family has been divided into subfamilies ranging from two (Tzvelev 1989) to six (Clayton and Renvoize 1986), and more recently the family has been divided into 12 subfamilies (Takhtajan 2009;Reveal 2012;Soreng et al. 2017Soreng et al. , 2019Stevens 2017).
In Egypt the grasses are the largest family of flowering plants with 284 species belonging to 103 genera and 22 tribes (Ibrahim et al. 2016). The most comprehensive account of the family in Egypt was done by Täckholm et al. (1941). Other treatments of the grasses of Egypt include Täckholm (1974), Cope and Hosni (1991), Cope (2005), Boulos (2009), and Ibrahim et al. (2016).
The identification of grasses is usually based on the structure of the inflorescence and floral characteristics. However, in some cases it is necessary to identify grasses by its vegetative character if the flowers are not available. In such cases the vegetative characters can be used until a flowering specimen is obtained (Hosni and Ibrahim 2004;Ibrahim et al. 2016).
Phylogenetic studies using results from DNA sequences have changed the classification of the grasses and this paper follows the current use of a name as proposed in these papers. With the publication of the grasses of Egypt using a vegetative key (Ibrahim et al. 2016), the need for an updated floral key is apparent. Earlier traditional treatments of the grasses of Egypt, i.e., Cope and Hosni (1991) and Cope (2005) are outdated and it is often difficult to determine the current use name. Our paper presents a new key for the identification of grasses native and adventive in Egypt and is written for use by both trained botanists and interested amateurs. Therefore, we have included an introduction defining many terms used in the key. The key is designed to facilitate the identification and is simplified as much as possible using characters based on the inflorescence and spikelet. Our key refers only to Egyptian specimens and, in addition, we include a updated classification of all grasses found in Egypt.
The accepted names follow the Catalogue of New World Grasses (Soreng et al. 2015(Soreng et al. , 2017 using terminology found in Kellogg (2015), Clayton et al. (2016), Ibrahim et al. (2016Ibrahim et al. ( , 2018, and Herrera Arrieta and . Because the inflorescence of grasses takes a variety of shapes, it is convenient to group them into categories based on their morphology. Accordingly, the identification key is divided into two parts, a key of major groups based mainly on inflorescence characters followed by keys to the species within each group. Brief descriptions, synonyms, and illustrations of the species was provided in Ibrahim et al. (2016). The classification of each species in Table 1 follows Soreng et al. (2017Soreng et al. ( , 2019. GENERAL MORPHOLOGY Grasses are annual, biennial or perennial herbs and the root systems are fibrous, rhizomatous or stoloniferous. Flowering stems (culms) are usually unbranched, composed of several internodes and are mostly hollow, rarely solid throughout, and the solid nodes can sometimes be hairy. Leaves are borne solitary at the node and can be crowded at the base of the culm. Each leaf consists of a sheath, ligule and lamina. Leaf blades may be hairy or glabrous. The base of the leaf sheath is attached to the nodes and clasping the stems firmly with overlapping free or connate margins, sometimes with two small falcate or erect outgrowths at the mouth (auricles). At the junction of a sheath and blade is a ligule that can be membranous or hairy (often a line of hairs) but occasionally a ligule can be absent. Leaf sheaths are mostly linear, flat, and sometimes folded or rolled in various ways.
Flowers ( Fig. 1) are usually hermaphrodite, sometimes unisexual (male and female), anemophilous (sometimes autogamous, apomictic or entomophilous) small and inconspicuous. The perianth is usually represented by two or three, minute but up to six, inconspicu-ous hyaline scales (lodicules) which correspond to the inner perianth whorl of other monocots. Stamens are hypogenous, 1-6 in number but usually 3 with delicate filaments and two anthers that dehisce through terminal pores or longitudinal slits. The ovary is unilocular with a single ovule. There are usually two or three (rarely 1) styles, generally with plumose stigmas. In grasses the fruit or caryopsis is single-seeded with an adherent pericarp, although there are numerous species with free pericarps and these would technically be termed akenes.
The floral parts are placed between two bracts, the lower (lemma) and upper (palea). These two structures are collectively referred to as a floret. The floret is usually subtended by two glumes. Lemmas vary in size and texture like the glumes and differ in the number of veins (usually with an odd number of veins), their overall shape, and the nature of their attachment to the rachilla. Lemmas are often awned or mucronate near the apex, or the awn is borne somewhere along the dorsal back. Awns can be straight, keeled or twisted. The paleas are usually membranous, tightly enclosing the pistil and stamens. Paleas (sometimes reduced) usually have two major veins and are therefore 2-keeled. The lemma, palea, and reproductive structures are called florets. The characteristic floral structure in grasses (spikelets) consist of one to many florets distichously inserted on either side of a slender, jointed rachilla ( Fig. 1). Spikelets vary in size from minute (1 mm or less) to relatively large (1 or 2 cm). Each spikelet is usually subtended by two lower empty scales or glumes. Glumes are variously veined and sometimes bear one or more awns. The base of a spikelet or floret is sometimes enlarged and hardened into a small knob or stalk (often sharp) called a callus. Glumes may be shorter than the adjoining lemma or longer and sometimes can be long enough to enclose the entire spikelet, or one or both glumes may be reduced or absent. Spikelets may be dorsiventrally compressed, laterally compressed, or terete.    The inflorescence (synflorescence) is usually compound, composed of simple or complex aggregation of primary inflorescences (spikelets) often produced on a central axis (rachis) which may be terminal, rarely axillary, or compound and rebranched (Fig. 2). Spikelets may be arranged in spikes, racemes or panicles (open or contracted). In spikes, the spikelets are attached directly (sessile) to the unbranched main axis without pedicels. Racemes are unbranched inflorescences with each spikelet borne on a single pedicel directly on a branch axis. Multiple racemes can be arranged digitally or scattered along the rachis. Open or contracted panicles are inflorescences in which the main axis has several lateral, whorled or individual indeterminate branches with each branch terminating in a pedicellate spikelet. Spiciform panicles is where contraction has proceeded to the point where individual branches are closely appressed or adherent to the central axis. Inflorescences can sometimes be subtended by a bladeless sheath known as spatheole.