Monocotyledons are plants that have only one cotyledon. They also have other characteristics, such as flower parts in multiples of threes. This means they could have three, six or nine petals, or they could have sepals that make up their flowers. They also have adventitious roots. These are roots that can grow from almost any part of the plant that comes into contact with the soil, such as the stem. Also, if you look closely at the leaves of a monocotyledon plant, you will see that the veins of the leaves are parallel.