Class Liliopsida (Monocotyledons)

Embryo, when differentiated, always with one cotyledon. The cotyledon usually with two main vascular bundles. Leaf venation striate or of derived types, mostly arcuate-striate or longitudinally striate (parallel), less often palmate-striate or pinnate-striate, almost always more or less closed at the apex (the veins emerging from the leaf base usually run together again at their apices). Leaves usually not clearly divided into petiole and lamina, less often more or less differentiated, but in these cases the “petiole” and the “lamina” are not homologous to those of magnoliopsids (are of secondary origin), often with sheathing base. Leaf traces usually numerous. Prophylls (including bracteoles) usually solitary and nearly always adaxial. Vascular bundles usually without cambium or rarely with vestigial cambium only. Vascular system of the stem usually consists of many separate scattered bundles or sometimes of two or more rings of vascular bundles, and the axis mostly attains its full diameter early, after which no increase in thickness takes place; only in some groups does thickening of the axis occur by means of division and enlargement of ground parenchyma cells (so-called diffuse secondary growth), as in palms, or by means of special kind of cambium that arises in the parenchyma outside the primary vascular system, as in some herbaceous and woody Lilianae. Sieve-element plastids of P-type with several to numerous cuneate (triangular) crystalloid bodies (lacking in all magnoliopsids studied except Saruma and Asarum in Aristolochiaceae). Phloem without parenchyma. Usually without clearly differentiated bark and pith. The primary root is usually ephemeral, dries out early in the growth of the plant, and is replaced by an adventitious root system that develops from the stem or (as in grasses) directly from the hypocotyl. Ontogenetically root cap and root epidermis are of different origin. Usually herbs, but often secondarily arborescent plants (primary woody plants are absent among the monocots). Flowers usually 3-merous, sometimes 4- or 2-merous, very rarely 5-merous. Nectaries predominantly septal. Pollen grains mostly 1-colpate (sulcate) or of derived types, often 1-porate.