Flowering plants, including trees and shrubs, are divided into two groups: monocot and dicot. This distinction is based in part on the number of flower petals, stamens and the growth pattern of the leaf veins. Monocot flowers have flowers with three petals or in multiples of three. The stamens of monocot flowers also appear in multiples of three. The leaf veins of monocot flowers, similar to grass (which also belongs to the monocot group), contain a central vein that is parallel to the leaf margins. If more than one leaf vein is present, they will grow parallel to each other. By contrast, leaves of dicot flowers contain a netlike structure of veins within their leaves, similar to the leaves on most deciduous trees, which are classified as dicots.
One of the largest and most diverse genuses of flowering plants, orchids (Orchis spp.) are classified as monocots due to their number of flower petals. Monocots have either three flower petals or multiples of three petals, and their elongated leaves contain parallel veins. Orchids are widely grown as indoor potted plants. Grow them in a mixture of bark, sand and perlite, repotting every two years. Put them in a bright location, away from direct sun. Provide orchids with extra humidity by misting daily or using a humidifier. New hybrids have been developed with long bloom periods---often eight weeks or more.
All varieties of lilies (Lilium spp.) are monocots. Virtually every variety of lily flower contains six petals, which is indicative of a monocot flower. They generally contain only three stamen, although some varieties contain six. Garden lilies are grown from bulbs planted in early spring. Flowers bloom from late spring through late summer, depending on the variety. Most varieties of lily are hardy through USDA zone 4, with some varieties hardy through zone 3 with adequate winter protection.
With their three upper petals that stand up and three bottom or "bearded" petals, irises (Iris spp.) are also considered monocot flowers because they have a petal count that is a multiple of three. Their thick, straplike leaves contain only a center vein that is parallel to the leaf margins, typical of monocot leaf structure. Plant iris rhizomes in full sun to part shade in well-drained, not overly fertile soil. Plant the rhizomes just below the surface of the soil; iris rhizomes planted too deep will not bloom. Divide iris every three to four years, shortly after they finish blooming.