Grasses and palms In Mexico, there are around 4,700 species (Villaseñor, 2004) belonging to 58 families of flowering plants of the monocotyledon group (Class: Monocots or Liliopsida). A sample of 15 families is presented here, selected either for their diversity in Mexico, for being restricted to Mexico, or for their uniqueness.
The grasses and palms group includes a diverse range of species, some of which are controversial. It includes agaves and yuccas, bromeliads, grasses, sedges, orchids, “bird of paradise” plants and palms. There are very few fossil records of monocots and relatively little is known about their origin and evolution. This has led to great discussion about the families and groups at the top of this taxonomic category. The group is characterized by having only one embryonic leaf or cotyledon in each seed. They are distinguished from the other group of flowering plants (the Dicotyledons or Magnoliopsida) by the following:
The ribs of the leaves are all parallel:
 The flowers (petals and sepals) are almost always divided into 3 segments or multiples of three
Conducting tissues (xylem and phloem) are widely dispersed and are not arranged in a ring as in the dicotyledons
They have a single cotyledon in the embryo
Stems have no secondary vascular tissue growth and therefore some species lack thickness.
Stems have almost no branches
In herbaceous species, the stem is hollow
The leaves normally have a sheath surrounding the stem
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