Monocots and dicots are the two broad groups of flowering plants (Division Magnoliophyta). While it is generally easy to distinguish most dicots and monocots from one another, the basis for the split in classification is a characteristic of the developing embryo, a feature that is no longer observable on the adult plant unless one can access the internal structure of a seed. Therefore, the following characteristics can be applied in the absence of knowledge about the cotyledon. However, be mindful that no 'single' characteristic will absolutely distinguish a dicot from a monocot, other than by definition monocots have one cotyledon and dicots have two. In general, monocots are simpler in structure than dicots, although monocots evolved from dicots.
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In monocot stems, the vascular tissues — the phloem and xylem — are in bundles scattered throughout the stem, and they typically lack a vascular cambium. In dicot stems, the phloem and xylem are in rings around each other. They nearly always have cambium. Despite a pine's stem structure resemblance to dicots, it is not a dicot. Pine is a conifer, which is not a flowering plant.
Partly as a consequence of the arrangement of the vascular tissue, in monocots, there is very little new phloem and xylem added to the stem. Thus, monocot stems do not grow significantly thicker each year. Any change in thickness is due to the cellss getting slightly larger. For this reason there are very few monocot trees (palmss being an important exception). On the other hand, dicot stems can add new vascular tissue and thus grow thicker with time. Most flowering trees are dicots.
In monocot roots, the phloem and xylem alternate like the spokes of a wheel. In dicot roots, there is a single, X-shaped mass of xylem at the centre, with phloem between the arms of the X. Throughout the whole plant, monocots have more vascular tissue than dicots of similar size.
Monocot roots grow from nodules on the stem, forming prop roots if close to the surface. In dicots, root growth is from the apical meristem, and often centered around a tap root.
The veins in monocot leaves are usually parallel, although palmate (arising from a common point at the base of the leaf) vein patterns are common. Dicot leaves have a branching vein network, rather like a feather, but can also be palmate.
Monocot flowers have flower parts in multiples of three. Dicot flower parts are in multiples of four or five. Monocot pollen has a single pore on the outer layer. This means it is monosulcate. Dicot pollen is triporate. In other words, it has three pores on the stem.