Dicots are one of the two big groups of flowering plants, named for the two seed leaves packed inside each seed.1Journal of Plant Pathology & Microbiology. Seed Leaves to Harvest: The Ecological and Economic Tapestry of Dicotyledons With over 175,000 species, they include most of the broad-leaved plants people grow and eat, from beans and tomatoes to roses and oak trees.2Journal of Plant Pathology & Microbiology. Seed Leaves to Harvest: The Ecological and Economic Tapestry of Dicotyledons The seed leaves are only the starting clue, though. The plant you see above ground carries a matching set of signs in its leaves, stems, roots and flowers, so spotting a dicot works like a checklist, where several traits agreeing matters more than any one of them.
The Five Traits That Mark a Dicot
- Seed: two seed leaves, called cotyledons, sit in the embryo. Monocots (grass-like flowering plants with one seed leaf) have just one.
- Leaves: the veins form a branching net, while monocot leaves usually have parallel veins.3PubMed Central. Developmental regulation of leaf venation patterns: monocot versus eudicots and the role of auxin
- Stems: vein bundles sit in a neat ring near the outside of the stem, while monocots scatter them.4Key Characteristics of Dicot Plants Explained. Key Characteristics of Dicot Plants Explained
- Roots: usually one main taproot with smaller side roots, while monocots grow a fibrous mat of similar roots.5University of Nevada, Las Vegas. Key Characteristics of Dicot Plants Explained
- Flowers: petals and other parts come in fours or fives, or multiples of these, while monocots favour threes.6Lumen Learning. Biology 2e
A plant showing three or four of these signs is probably a dicot even if one sign is unclear, though a few groups, covered below, break the pattern.
7Journal of Plant Pathology & Microbiology. Seed Leaves to Harvest: The Ecological and Economic Tapestry of Dicotyledons8Journal of Plant Pathology & Microbiology. Seed Leaves to Harvest: The Ecological and Economic Tapestry of Dicotyledons
On a real plant, start with the leaves. They are on the plant most of the year and need no tools, so a glance at the vein pattern comes first. Flowers give the cleanest count, but only while the plant is blooming, so use them to confirm rather than to start. Seed leaves show only on seedlings a few days old, and checking roots or a stem cross-section means digging up or cutting the plant. Keep those for when leaves and flowers leave you unsure.
Beans, sunflowers, tomatoes, roses and oaks are dicots. Grasses, lilies, onions, palms and corn are monocots. Holding a bean leaf next to a blade of grass makes the vein difference obvious in seconds.
Inside a Dicot Seed
A typical dicot seed has a thick seed coat wrapped around an embryo with two seed leaves.9Pearson. General Biology Study Guide: Exam 2 Key Concepts & Review Both seed leaves are connected to the baby plant by tiny veins, so food can flow from them straight into the growing shoot and root.10Lumen Learning. Development of a Seed and Fruit
The food itself is stored in one of two ways. In many dicots, such as beans, the food supply is moved into the seed leaves early, so they become thick and fleshy.11Lumen Learning. Development of a Seed and Fruit In other dicots the food stays in a separate tissue.12Lumen Learning. Development of a Seed and Fruit In those seeds the seed leaves act like sponges, soaking up food the seed breaks down during sprouting.13Lumen Learning. Development of a Seed and Fruit
You can see this for yourself. Soak a dry bean overnight so the coat softens, then peel it off with your fingernail. The bean falls open into two fleshy halves, and those halves are the two seed leaves. Look where they join: a tiny curled shoot and root are tucked there, which is the baby plant itself. A corn kernel will not split into two matching halves like this, which shows the monocot difference you can handle yourself.
After sprouting, the seed leaves of beans and squash push above the soil as the first green pair. They often look rounder and simpler than the true leaves that follow. Once the true leaves take over feeding the plant, the seed leaves shrivel.
Net-Veined Leaves and Ringed Stems
Dicot leaves have a main vein or veins with smaller veins branching off and joining into a mesh.14PubMed Central. Developmental regulation of leaf venation patterns: monocot versus eudicots and the role of auxin Monocot leaves tend to have veins running side by side from base to tip.15PubMed Central. Developmental regulation of leaf venation patterns: monocot versus eudicots and the role of auxin
Hold a maple or rose leaf up to the light and you see a web of fine veins connecting in a mesh. A grass blade or lily leaf shows straight lines running side by side along its length.
In a dicot stem, the vein bundles, which carry water and sugar, are arranged in a ring.16Key Characteristics of Dicot Plants Explained. Key Characteristics of Dicot Plants Explained Outside the ring is a layer of packing tissue, and inside is soft central pith.17Key Characteristics of Dicot Plants Explained. Key Characteristics of Dicot Plants Explained Running through the bundles is a thin growth layer whose cells divide to thicken the stem.18Visible Body. Monocot and Dicot Stems
To see the ring, slice a soft stem such as sunflower or bean straight across with a sharp knife. Look for a ring of small dots near the edge, which are the vein bundles. Slice a corn stalk and the dots are scattered across the whole cut face instead. Choose a young, soft stem, since an older woody stem has merged its bundles into solid wood and no longer shows separate dots.
Taproots and Flower Parts in Fours and Fives
In most dicots the seedling’s first root swells into a main taproot that lasts the plant’s whole life.19University of Nevada, Las Vegas. Key Characteristics of Dicot Plants Explained Smaller and smaller side roots branch off it.20University of Nevada, Las Vegas. Key Characteristics of Dicot Plants Explained
Carrots, radishes and dandelions show the taproot plainly, since the thick main root is the part you eat or struggle to remove. Pull a dandelion and it often snaps, leaving the deep root behind, because that root anchors it so well. Pull up a clump of grass and you get a shallow tangle of many similar fine roots instead. Taprooted plants resist drought by reaching deeper water, and they dislike being moved once established.
Dicot petals usually number four or five, or multiples of four or five, while monocot petals usually come in threes or multiples of three.21Lumen Learning. Biology 2e To count properly, include the sepals, the small green parts beneath the petals, since they often follow the same number. Buttercups and wild roses show five petals, while mustard family flowers such as broccoli blossoms show four. Double garden flowers have extra petals bred in, so check the sepals or look at a wild form of the plant. Fused petals, as in a petunia, hide the count, but the tips or lobes of the flower can still show it.
Why So Many Dicots Become Wood
The growth layer is a ring that produces wood toward the inside of the stem and food-carrying tissue toward the outside.22PubMed Central. Vascular Cambium: The Source of Wood Formation More than 90% of its cells are long and run up and down the stem, producing these layers.23PubMed Central. Vascular Cambium: The Source of Wood Formation Other cells make thin ribbons running from center to edge that move and store materials sideways.24PubMed Central. Vascular Cambium: The Source of Wood Formation
As most dicot stems and roots thicken, a corky layer replaces the original skin and protects the plant.25PubMed. A molecular framework to study periderm formation in Arabidopsis Even small non-woody dicots can thicken this way in their roots.26PubMed. A molecular framework to study periderm formation in Arabidopsis
A tree stump shows all of this at once. The rings are yearly layers of wood laid down by the growth layer. Pale lines running from the center to the edge are the sideways ribbons carrying and storing materials across the trunk. The bark on the outside is the corky layer that replaced the original skin as the trunk thickened. Palms are monocots and lack a growth ring, so their trunks do not add yearly wood and a cut palm trunk shows no rings.
Plants That Break the Rules
Magnolias and their relatives were long counted as dicots, but they belong to a separate, older group.27Wikipedia. Magnoliids They usually have net-veined leaves like dicots.28Wikipedia. Magnoliids Their flowers, however, often have parts in threes, and their pollen has a single opening.29Wikipedia. Magnoliids Their flower parts can also be numerous and spirally arranged rather than in neat fours or fives.30CronkLab. Magnoliids
Other plants can fool you too. Some monocots, such as certain arums, have net-like veins, so veins alone can mislead. Some dicots with narrow leaves look like they have parallel veins, because their veins run lengthwise.
The main dicot group is now often called eudicots, meaning true dicots, as scientists split off older groups like magnolias. Garden guides and school books may still use the older, broader word dicot, so expect both names.
Why Dicots Matter in Gardens and Farms
Legumes such as beans, peas and clover, all dicots, host soil bacteria in small root lumps called nodules.31PubMed Central. Regulation of Symbiotic Nitrogen Fixation in Legume Root Nodules The bacteria turn nitrogen from the air into a form plants use, in exchange for sugars from the plant.32PubMed Central. Regulation of Symbiotic Nitrogen Fixation in Legume Root Nodules Crops grown after or alongside legumes benefit from the extra nitrogen.33PubMed Central. Regulation of Symbiotic Nitrogen Fixation in Legume Root Nodules Farms worldwide gain about 50 to 200 million tonnes of nitrogen a year this way.34PubMed Central. Regulation of Symbiotic Nitrogen Fixation in Legume Root Nodules
At home, plant beans or peas in a bed where hungry crops, such as leafy greens, will grow next. Pull up a bean plant and look for small pinkish nodules on the roots, which show the bacteria are at work. After harvest, cut the plant at soil level and leave the roots in the ground, so the nitrogen in them returns to the soil.
On the dinner plate, tomatoes, potatoes, lettuce, apples and sunflowers are dicots, so much of a salad and a fruit bowl comes from this group. Rice, wheat and corn are monocots, so the staple grains come from the other side.