How to distinguish a monocot from a dicot





Monocots and dicots are the two broad groups of flowering plants (Division
Magnoliophyta). While it is generally easy to distinguish common 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 the seed. Therefore, the following charateristics 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.

Stem

In monocot stems, the vascular tissue, the phloem and xylem are in bundles
scattered throughout the stem, and they usually 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
dicot, it is not a dicot. Pine is a conifer, which is not a flowering plant.

Partly as a consequence of the above, 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 cells
getting very slightly bigger. This is why there are very few monocot trees
(palms being an important exception). On the other hand, dicot stems can add
new vascular tissue and thus grow thicker yearly. Most flowering trees are dicots.

Root

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.

Leaf

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.

Flower

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.