2.7.1: Monocots and Eudicots

Learning Objectives

• Compare and contrast monocots and eudicots.
• Differentiate between monocot and eudicot flowers and leaves.

Of over 400 families of angiosperms, some 80 of them fall into a single clade, called monocots because their seeds have only a single cotyledon. The remainder have seeds that produce two cotyledons (Figure \(\PageIndex{1}\)). This group includes some early diverging angiosperms (ANA grade families and magnoliids), but the large majority of these occupy a single clade called the eudicots. In addition to developmental features, there are a few morphological and anatomical traits you can use to distinguish between these two major groups.

Figure \(\PageIndex{1}\): Monocots like the grass shown on the left produce only one cotyledon (mono- for one, -cot for cotyledons). Eudicots (on right), also sometimes called dicots, get their name from having two cotyledons (eu- for true, di- for two). Cotyledons are the first, fleshy leaves that enveloped the embryo as it grew. Image from Pengo, CC BY-SA 2.5, via Wikimedia Commons.

Monocots

Monocots have a single cotyledon in their seed, parallel venation in their leaves (Figure \(\PageIndex{2}\)), flower parts in multiples of three (3-merous, see Figure \(\PageIndex{3}\)), and vascular bundles dispersed throughout the stem in concentric circles. Monocots do not have true secondary growth, though some (such as bamboo) form tough, woody stems.

Figure \(\PageIndex{2}\): These two monocot leaves both have parallel venation. It is more obvious in the second leaf. However, if you look closely at the first leaf, you'll see that those veins do not cross each other. Instead, they travel in the same direction without overlapping, just as in the leaf on the right. Photos by Maria Morrow, CC-BY 4.0.

Figure \(\PageIndex{3}\): This Trillium is a monocot, which you can tell because it is 3-merous. There are three sepals, three petals, six stamens, and three stigma lobes visible in the gynoecium. Monocots have floral parts in sets of three (3-merous). Photo by Maria Morrow, CC-BY 4.0.

Some major groups of monocots are:

• palms (Arecaceae)
• orchids (Orchidaceae)
• yams, sweet potatoes (Dioscoreaceae)
• lilies, onion, asparagus (Liliaceae)
• bananas (Musaceae)
• all the grasses (Poaceae), which include many of our most important plants such as
  • corn (maize)
  • wheat
  • rice
  • and all the other cereal grains upon which we depend so heavily for food as well as
  • sugar cane and bamboo

Eudicots

Eudicots have two cotyledons in their seeds, netted venation in their leaves (Figure \(\PageIndex{4}\)), flower parts in multiples of 4 or 5 (4-merous or 5-merous, see Figure \(\PageIndex{5}\)), and vascular bundles in the stem arranged in a radial pattern like spokes of a wheel.

Figure \(\PageIndex{4}\): A skeletal holly leaf shows the network of vascular tissue. The lignified xylem and phloem fibers break down far more slowly than the parenchyma cells of the leaf. As the rest of the leaf tissues decompose, the lignified vascular tissue is left behind. This reveals the netted pattern of increasingly smaller side branches found in eudicot leaves. Photo by Maria Morrow, CC-BY 4.0.

Figure \(\PageIndex{5}\): Eudicot flowers tend to be 4-merous or 5-merous. The Clarkia flower (first image) is 4-merous. We cannot see the calyx, but there are four petals, 8 stamens, and 4 stigma lobes. The flax flower (second image) is 5-merous. There are five sepals poking out between the five petals and 5 stamens (with blue anthers!). The number of stigma lobes is not distinguishable in this image. Photos by Maria Morrow, CC-BY 4.0.

Attribution

Content by Maria Morrow, CC-BY