Tag Archives: pollen

Giant Ragweed Ambrosia trifida

Every year I watch the giant ragweed start to grow. It lines the road. It surrounds the barn. It fills the barn lot and adjacent pasture. Its population gains every year.

The pollen spikes start growing. They get six to ten inches tall lined with green balls. When the green balls open, releasing pollen into the air, the boxes of tissues get set out around the house.

By mid September the spikes are only brown stalks. The pollen is gone for the year. Now the seeds scatter across the ground promising a new, bigger crop of giant ragweed next year.


Ambrosia trifida L.

July to September                                       N                                 Family: asteraceae

                                                                                                            Tribe: Heliantheae

giant ragweed male flowers

Male flowers

Flower: There are separate male and female flowers. The male flowers are in hanging bundles on a spire. One main and several auxiliary spires can come from the tips of each branch. The female flowers are tucked into swirls of bracts at the base of the spires. The flowers are wind pollinated.

giant ragweed female flowers

Two female flowers

Leaf: Opposite leaves are rough, green on the upper side, slightly paler on the under side and covered with very short hairs. Many of the leaves have three lobes but can have five or none. Main veins run out each lobe. The leaves have long petioles that can be winged. each leaf can reach twelve inches long and eight inches wide.

giant ragweed under leaf

Stem: The thick, ridged stem can reach 12 feet in height. It has branches. The stems are light green, rough to the touch, stiff, hollow and have lines of short hairs. The bases of tall stems thicken, become woody and can be three inches in diameter.

giant ragweed leaf

Root: The annual roots are fibrous around a taproot.

giant ragweed stem

Fruit: The seed is tan with an ovate base. the top has a main rounded spike surrounded by a ring of lower, rounded lobes.

giant ragweed fruit

Habitat: This plant prefers full sun, good soil and moisture. It is not particular and grows in a wide variety of places especially disturbed ground and pastures.

Edibility: Cattle, goats and deer eat giant ragweed. The seeds have a tough coat but can be eaten.


Giant Ragweed

Great Ragweed, Horseweed, Buffalo Weed

giant ragweed plant

Giant Ragweed is considered a noxious weed in some states. it does tend to form dense colonies once established in an area. It is the most abundant ragweed.

The plants are annuals and produce lots of seeds. These germinate in mid to late spring. The seedlings grow rapidly often in dense stands, many of which die from the competition.

Although, under ideal conditions, Giant Ragweed can to 12 feet with stalks three inches in diameter, tough enough to require a saw to cut them, many times the plants are cut or grazed or mowed off. The plants then put out new branches quickly reaching two to three feet and blooming. Even six inch plants will put up single spires.

As are other ragweeds, Giant Ragweed is wind pollinated. Each plant produces tremendous amounts of pollen. This is a major cause of hayfever in late summer.

Bees still visit Giant Ragweed male flowers to gather pollen. They may knock some pollen down on the female flowers, but do not visit them. They leave the pollen spikes heavily laden.

Archeologists find caches of Giant Ragweed seeds at various sites. The seeds are tough but do contain edible oils. Few birds can eat them due to the tough shells.

OS15 Male Pumpkin Flowers

Pumpkins have two kinds of flowers. One flower makes pollen and is called a male flower. Most flowers on a pumpkin plant are male flowers. These have long thin stems called petioles. On the day you want to do this Investigation, go out early in the morning and pick a male flower. It may have insects in it. Use a long grass stem to push them out. Don’t knock the flower about, especially upside down or all the pollen will fall out! Put the flower into a glass of water until you are ready to look it over. It will wilt in just a few hours so let’s start early and find out about a male flower.


Question: What parts are in a male pumpkin flower?


Male Pumpkin Flower

male flower

A male flower has a long, slim petiole. They rise up from leaf nodes, places where the leaf petioles join the pumpkin vine.

Metric ruler


Magnifying glass


Slide and coverslip



Step 1: Open your Science Journal, write “Investigation 15” and the date.

Step 2: Examine the outside of the male flower. Measure how tall it is. Compare it to the diagram of a flower and label your drawing with the parts.

inside male flower

Looking inside a male flower it is easy to see the flower has five petals joined together. The stamens are joined into a single column. Around the base of the column is a trough evidently filled with nectar as insects congregate there. Larger insects would come in contact with the pollen on the stamen column getting it on their bodies so the pollen will be carried off when the insect leaves hopefully stopping by a female flower next.

Step 3: Smell the inside of the flower.

Step 4: Carefully tear or cut off the petals of the flower and lay them out on the table.

Step 5: Examine the petals. Compare the inside and outside surfaces – look, color, feel.

Step 6: Examine the stamen. Measure the stamen. Touch the stamen. Draw and describe what you observe.


Splitting a stamen lengthwise shows the inside is solid. The yellow concentric loops form a thin skin on the outside of the top half of the stamen.

Step 7: Put a drop of water on a slide. Put some of the pollen from the stamen on the water. Put on the coverslip.

Step 8: Examine the pollen with the microscope.

Step 9: Carefully slice the stamen in half lengthwise and examine the inside.

magnified stamen

Magnifying the top of the stamen shows the concentric loops are yellow ridges on a pale base.



male flower petals

The inside of the joined petals is smooth, slick, changing from yellow at the bottom to orange at the top. Large veins run down the center of each petal. The flower wilts quickly after being picked.

outside male flower petals

From the outside the joined petals are more greenish yellow at the base but still orange at their tops. Three veins are obvious on each petal lthough only the middle one is really big on the inside. The petals still feel smooth but don’t have a slick feel.


Explain why you think a pumpkin flower has only one or has many petals joined (fused) together.

If a pumpkin flower has fused petals, how many petals are there? How can you tell?

What advantages would fused petals instead of separate ones give a pumpkin flower? (You might want to look at some flowers on your pumpkin plant in the early morning to get some ideas.)

Each seed in a pumpkin flower needs one grain of pollen to become a seed. Why are there so many more male flowers making pollen than female flowers (These have tiny pumpkins under them.)?

Why do you think the flower makes so much pollen since only one grain or piece is needed for each seed?

male flower stamen

The large stamen has a big base with three feet. It sits in the center of a moat. The five sepals and petals are on the outside edge of this moat. The top of the stamen looks like an unexpanded mushroom but with concentric loops all over it. Pollen is found in the troughs of the loops.

Many flowers have lots of little stamens. A pumpkin flower seems to have only one. Does the pumpkin flower have fused stamens? Explain why you think so.

Different kinds of plants have pollen grains (separate pieces of pollen) with different shapes. Archeologists use fossil pollen to identify the kinds of plants that grew in an area long ago. What special things about a pumpkin pollen grain do you see?