Monocotyledons

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the Monocotyledons(alias:Monocots) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. There are about 59,300 species of monocots. The largest family is the orchids, with more than 20,000 species. They constitute one of the major groups into which the flowering plants have traditionally been divided; the rest of the flowering plants have two cotyledons and are classified as dicotyledons, or dicots.

Monocotyledons is a common group of higher plants. It is named because the embryo usually has one cotyledon. In terms of biological classification, it belongs to the plant kingdom, angiosperm, and monocotyledons. Among them, Monocotyledons are called "Liliaceae", which stand side by side with the "Magnolia" of dicotyledonous plants. Modern genetics shows that monocotyledonous plants are actually evolved from ancient dicotyledonous plants.

In the traditional Cronquist taxonomy, the monocotyledonous plants are called "Liliaceae", which stand side by side with the dicotyledonous plants Magnoliaceae, and it is believed that monocotyledonous plants are composed of extinct primitive dicotyledonous plants such as buttercups or Evolved from the ancestor of water lilies. H． Huber believes that monocots and buttercup dicots are the extreme two wings of the same natural unit, and Anemone, Aristolochiaceae, Nymphaeaceae and Pepperaceae are the links between the two wings. That is, Huber believed that the origin of monocots was related to the ancestors of buttercups. And A． Cronqvist believes that the dicotyledonous plants that can be used as the origin of monocots should be herbaceous, with weak cambium activity, normal perianth (that is, perianth not specialized), single-pore pollen, detached carpels and Taxon of lamellar placenta. Among the existing dicotyledonous plants, Nymphaeaceae has such special features. Although it is not the direct ancestor of monocotyledonous plants, there are fossils similar to Nymphaeaceae in the dicotyledonous plants of pre-monocotyledonous plants, which were found in the Late Cretaceous Al Albian epoch.

In 1964, H. Melchio divided the monocotyledon class into 14 orders including Helobial, and A. Takhta and A. Cronquist changed the class to Liliopsida.

But later research gradually made botanists realize that monocots actually evolved from ancient dicotyledonous plants and are one of the specialized branches of dicotyledonous plants, which makes the traditional classification of dicotyledonous plants a parallel system. group is no longer considered a valid classification.

The APG taxonomy of angiosperm genes has determined that monocots are a monophyletic branch under the angiosperm branch, and the classification is effective, and the monocot branch has been established. There are many changes in the internal classification, including the denial of the blue order. Multiphyletic groups were classified, and new orders such as Aspartame and Dioscorea were established.

The 2003 revision of the APG II taxonomy also uses this classification method and includes all plant species in the class Monocots in the traditional classification.

The APG II classification divides plants in the monocotyledonous clade into 10 orders and 2 separate families, some of which are included in the commelina clade (a genetic relative group).

The revised APG III taxonomy in 2009 promoted the separate Petrosaviaceae to Petrosaviales

Monocotyledoneae are a class of angiosperms. The leaf veins are often parallel veins, the mosaic leaves are basically three in number, and the seeds are characterized by one cotyledon. Most of them are herbaceous, few are woody, the vascular bundles are scattered, and the plastids of the sieve tubes have wedge-shaped protein inclusions. Except for some plants of the order Lilium, the vascular bundles usually have no cambium. Stems and roots generally have no secondary hypertrophy growth. Although some plants have secondary growth, the cambium is different from that of dicotyledonous plants, that is, the secondary phloem and secondary xylem are formed inside the cambium. Bamboo, coconut, pandanus Although it has a solid tree-like trunk, it still has closed vascular bundles, the same as herbaceous monocots. The main root stops growing earlier and sends out many slender adventitious roots to form fibrous roots (see root). Leaves are generally single, entire, rarely palmate or pinnately split leaves or even palmate or pinnately compound leaves; leaves and petioles are undifferentiated, or have been clearly differentiated, often with a part of the petiole clasping into a leaf sheath; a part Monocots also have stipules, but not necessarily the same as those of dicotyledons; in general single, entire leaves, the apex of the first lateral vein fuses into a closed leaf vein system at the leaf margin or leaf tip, Palmaceae, The leaves of Zingiberaceae and Musa have secondary veinlets, which are parallel to the first lateral veins to form special parallel veins. Many plants with compound leaves, such as coconut, are often formed by splitting the leaves themselves. In addition, the compound leaves of some plants are formed by opening pores, and some are formed by differentiation of leaflet primordia. Mosaic leaves mostly 3 numbers, rare 4 or 2 numbers, except for the stamens of some species of Zingiberaceae, there are no 5 numbers. In primitive groups, detached carpels and pollen of single groove are mostly seen. The seed has 1 cotyledon, and the embryo is often displaced. It looks like the cotyledon is terminal, and the embryo is lateral. When germination, the radicle first breaks through the seed coat, followed by the base of the cotyledon sheath surrounding the germ, hypocotyl Generally very short or suppressed, the nutrients in the endosperm are absorbed by the top of the cotyledon. There are also parts of the embryo that do not differentiate.

Monocotyledons have six major organs, namely root, stem, leaf, flower, fruit, and seed. The root is the vegetative organ, usually located below the surface; Contains chlorophyll; the flowers are born on the receptacle, and the reproductive organs are wrapped in the middle of the petals; the fruit is developed from the pistil of the flower, and the seeds are wrapped in the fruit; the seeds are propagules, which can develop into new plants.