Dicotyledon

Lore & Background

Largely from the 1990s onwards, molecular phylogenetic research confirmed that dicotyledons are not a monophyletic group—that is, they do not consist of all descendants of a common ancestor. Instead, a number of lineages, such as the magnoliids and groups now collectively known as the basal angiosperms, diverged earlier than the monocots did; monocots evolved from within the dicots as traditionally defined. The traditional dicots are thus a paraphyletic group. The eudicots are the largest monophyletic group within the dicotyledons. They are distinguished from all other flowering plants by the structure of their pollen: eudicots have tricolpate pollen (grains with three or more pores set in furrows called colpi), whereas other dicotyledons and monocotyledons have monosulcate pollen (or derived forms) with a single sulcus. Aside from cotyledon number, other broad differences have been noted between monocots and dicots, although these have proven to be differences primarily between monocots and eudicots. Many early-diverging dicot groups have monocot characteristics such as scattered vascular bundles, trimerous flowers, and non-tricolpate pollen. In addition, some monocots have dicot characteristics such as reticulated leaf veins.

Reader's Guide

The dicotyledons historically served as one of the two primary divisions of flowering plants, a classification that persisted for centuries. However, molecular phylogenetic research from the 1990s onward revealed that the group is paraphyletic, as monocots evolved from within the dicots. This finding reshaped botanical taxonomy, leading to the recognition of the eudicots as the largest monophyletic subgroup within the dicots, defined by tricolpate pollen. The legacy of the dicot concept remains in its practical utility for describing many flowering plants, though modern systems like the APG IV treat it as a paraphyletic assemblage. The term continues to appear in historical and some contemporary classifications, such as the Cronquist system, where dicots are treated as the class Magnoliopsida. The shift from a simple dicot-monocot dichotomy to a more nuanced phylogenetic tree underscores the ongoing refinement of plant systematics based on genetic evidence.

Did You Know?

• Dicotyledons were formerly divided into two groups with monocotyledons, based on the number of cotyledons in the seed.
• Molecular research from the 1990s onward confirmed that dicots are paraphyletic, with monocots evolving from within them.
• Eudicots, the largest monophyletic group within dicots, have tricolpate pollen, unlike the monosulcate pollen of other dicots and monocots.
• Some early-diverging dicot groups have monocot characteristics such as scattered vascular bundles and trimerous flowers.