Weeds: Dicot

Dicot (broadleaf) weed identification just like monocot identification can be challenging. The base plant identification parts are similar between monocots and dicots however there are additional characteristics that are critical in proper dicot (broadleaf) weed identification.

Leaf arrangement (Figure 30)

Alternate - leaf arrangement is characterized by a single leaf per node
Opposite - leaf arrangement is characterized by two and only two leaves at a node on opposing sides of the stem
Whorled - leaf arrangement is characterized by three or more leaves per node are arranged in a circular pattern

Figure 30. A picture of different types of leaf.

Leaf type (Figure 31)

Simple - a leaf that is undivided, meaning it has only one definite segment present between the stem and the end of the blade
Compound - leaves are divided into definite and distinct segments called leaflets
- Pinnately - leaflets are arranged on opposite sides of the leaf axis, similar to a feather
- Palmately - leaflets radiate from a central point, like fingers radiating from the palm of a hand.

Leaf shape (Figure 32)

Elliptic - leaves are broadest in the middle and narrower at either end
Linear - leaves are long and narrow with the sides being close to parallel to each other
Lanceolate - leaves are much longer than wide, with the widest point below the middle of the leaf
Spatulate - leaves look like a spatula, with the tip being rounded and gradually tapering to the base
Ovate - leaves are egg-shaped, lacking a pointed tip
Oval - leaves are round to oval, lacking a pointed tip
Cordate - leaves are heart-shaped

Figure 32. A picture of different shapes of leaf.

Leaf margin (Figure 33)

Smooth - the entire margins are smooth and do not have any teeth, notches or divisions
Dentate or Serrate - leaves have toothed or saw-like margin
Lobed - leaves have indentations along the margin that cut inward toward the leaf midvein

Figure 33. A picture of different types of leaf margin.

Leaf attachment (Figure 34)

Petiolate - leaves have a stalk (petiole) that attaches them to the stem
Sessile - leaves do not have a petiole and are attached directly to the stem
Clasping - leave are sessile and have a base that wholly or partly wraps around the stem

Figure 34. A picture of different types of leaf attachment.

Flower parts (Figure 35)

Sepals - outermost whole of leaf-like structures that protect the bud. Typically small and green in color, but may be just as colorful as the petals
Calyx - the collection of sepals
Petals - the next whorl of leaf-like structures. They are usually colorful and attractive
Corolla - the collection of petals
Tepals - petal-like structures which are found on some plants that do not have petals and sepals but just one undifferentiated whorl
Stamen - male reproductive organ consisting of an anther and filament
- Anther - bears pollen
- Filament - thread-like structure that supports that anther
Pistil - female reproductive organ consisting of the stigma, style and ovary
- Stigma - the tip of the pistil and receives pollen
- Style - the narrowed portion that connects the stigma to the ovary
Pedicel - is the stalk that attaches the flower to the stem

Figure 35. A picture of reproductive parts of a flower.

Asteraceae family unique features (Figure 36)

Florets
- Ray
- Disc
Bracts - leaf- or scale-like structures that surround the base of the flower

Figure 36. A picture of arteraceae family.

Flower shape (Figure 37)

Campanulate- bell-shaped flower with a wide tube and flared lobes (petal tips)
Cruciform - cross-shaped flower with four petals at right angles to one another
Head
Spurred
Papilionaceous - pea-shaped flower that have a large upper petal called the standard, two large side petals called wings and two lower petals often fused together called the keel which encloses the stamens and stigma

Figure 37. A picture of different flower shapes.

Inflorescence types (Figure 38)

Spike - the flower is attached directly to the stem and pedicles (stalks) are absent
Raceme - pedicels attach the flowers to the stem
Panicle - compound or branched racemes
Corymb - pedicles are different lengths with the pedicels at the base are longer than those near the top, giving a flat to rounded top
Umbel - a flat topped or convex inflorescence with the pedicels arising from a common point, like an umbrella
Helicoid cyme - coiled like a scorpion’s tail

Figure 38. A picture of different inflorescence types.

Did you Know?

There are multiple on-line sources to aid in weed identification such as University of Missouri Weed ID Guide which also available as a downloadable app.

Nebraska Soybean Board graciously provided the funding for the Soybean Management Guide.

Course authored by:

Amy Timmerman, Extension Educator, Aaron Nygren, Extension Educator, Brandy VanDeWalle, Extension Educator, Loren Giesler, Extension Plant Pathologist, Ron Seymour, Extension Educator, Keith Glewen, Extension Educator, Charles Shapiro, Extension Soil Scientist, Amit Jhala, Extension Weed Scientist, Don Treptow, Graduate Student