Poinsettias. Do Now: How many Poinsettias do you think are sold each year in the US?

Poinsettias

Do Now:

• How many Poinsettias do you think are sold each year in the US?

Answer

• Answer: over 52 million poinsettias are sold annually - more than all other potted flowering plants combined

How can we find out what plant family Poinsettias are in?

• Some clues:– Break one leaf and observe what happens

– Take a close look at the flowers• Are there any petals? Sepals?

• What most people believe to be the flower is actually a series of colored leaves called bracts; the flowers are the round yellow berry like clusters in the center of each group of bracts.

Flowers Nectar Glands

Each Anther is a separate flower

Bracts

Female Flower arises from the center of the cyathium

In each cyathium there are usually several male flowers but only one female flower, and that female is attached in the cyathium's center.

Identify the cyathium

How do you know which are the male flowers?

How do you know which is the female flower?

• Plants with cyathiums and individual male and female flowers attached to a cyathium is unique to the Euphorbiaceae family.

• Poinsettia = Euphorbia pulcherrima

• Also all euphorbs bleed a white latex when injured

• Other Euphorbs– Castor bean– Rubber tree– Yucca (Manioc)

Are all Poinsettias small?

• Poinsettias can grow to heights of up to ten feet

Why do you think the ones we commonly see sold are small?

Plants that are sold are kept small

• Many of the plants sold in stores are hybrids that have been bred to stay small

• Many are just cuttings from other plants that are kept small by pinching the growing tips

• Others are treated with growth regulating hormones to keep them small

How do you get one to bloom?

• Why do you think they always bloom in December?

• Which environmental cues do the plants use to bloom?

Answer

• In order to get a Poinsettia to bloom you must– Give them full sunlight (Tropical plant, or greenhouse

plant)– After a few months of long days, you must shorten

the day time– Once the nights grow longer the flowers will initiate

and the bracts will grow and turn red

• Why do you think the plant has red bracts around the flowers?

Answer

• Attracts pollinating birds,– Birds love to visit red and yellow flowers– Birds have no sense of smell so the flowers they

visit to waist energy making scents

• How would you pollinate the flowers?

Answer

• Of course you said place the pollen from the male flowers on the female flowers.

• But not so quick, female flowers mature first and become too old to receive the pollen from the same plant when the male flowers mature.

• How would you devise a solution?

Answer

• Take pollen from a different plant whose males flowers are mature at the same time as the female flowers from your plant are mature

Making cuttings

• If you want to multiply the number of plants you have you can make cuttings– Cut healthy looking stems from the original plant– Remove the leaves growing closest to the bottom

of the cutting– You can use rooting hormone to initiate root

growth on the cuttings• Dip the cuttings in hormone powder and place in googd

quality potting soil. Make sure the new plants are well watered.

HWChapter 13 page 131-136Answer questions 1-15