[This is the second in a series of three posts; the first post is: Poinsettias up close: where are the flowers? and the third is Poinsettia flowers part three: the female parts.]

Earlier this week I posted about finding the flowers in poinsettias (spoiler: the petals aren’t the big red structures!).  After writing that post, though, I realized it was missing a good closeup of the flower clusters themselves.  So, yesterday afternoon I took a quick break from my end-of-the-semester piles of grading and headed back to Orange Coast College’s Ornamental Horticulture Department to get a few more pictures.

The flowers of poinsettias (Euphorbia pulcherrima) are actually cyanthia: flowering structures composed of many individual male or female flowers surrounded by modified leaves.  Here’s what they look like:

To see that image larger, follow this link to see it as a large, high-resolution image.

That picture shows multiple cyanthia (flower clusters) at the end of a stem surrounded by a sea of red bracts (colored leaves associated with a flower). Each green ball tipped with red is an involucre, a cluster of bracts (leaves) fused into a cup-shaped structure that contains multiple male flowers and one female flower within it.

Let’s look at the involucres and their flowers even closer:

To see that image in all its glory, follow this link to see it as a large, high-resolution image.

Emerging from each involucre you can see red filaments supporting yellow anthers that are dusty with individual pollen grains.  The filaments are emerging from the multiple male flowers growing within each involucre.   Also emerging from each involucre you can see a number of dark-purple structures supported by short stalks; I believe these may be the stigmas and styles of the flowers (though this species is supposed to have only a single female flower per involucre with a stigma divided into three sections, so I’m not certain what those dark-purple structures are).

[edited 1/20/2012: the dark purple structures are indeed not the female flowers, as I write about in this post. I’m not at all sure what these small structures are. Anyone have any ideas?]

The bright yellow, liquid-filled structures attached to the involucre are nectar glands filled with nectar (to attract pollinators).  A few individual pollen grains are stuck to the surface of the left-most nectar gland.

I’ll leave you with a crop of that last image showing two cyanthia in more detail

And, if you want your own poinsettias to admire, head to Orange Coast College this Friday: they’re having their annual poinsettia sale, which is open to the public.  See my first post in this series for more information.

More pictures

To see more of my poinsettia pictures, head to my Poinsettia Gallery.

[This is the first in a series of three posts; the second post is: Poinsettia flower closeups take two: getting even closer and the third is Poinsettia flowers part three: the female parts.]

Orange Coast College’s Ornamental Horticulture Department is just plain awesome. The department’s landscaped gardens are easily the most beautiful spot on campus, they teach a wide array of neat classes (landscape design, plant propagation, cacti and succulents, etc.), and they’ve got the nicest faculty and staff around.

To help fund their department, and provide a lab opportunity for their plant propagation class, every fall the department rears thousands of poinsettias (Euphorbia pulcherrima) in their greenhouses for sale to the public. This year’s sale is this Friday (December 9), and their greenhouses are currently full of beautiful poinsettias.

I just had to take a look at the plants last week:

Many people think that the big red (or red and white, in the picture above) structures are the flower petals of poinsettias; they’re not.  The big red structures are bracts: specialized leaves associated with a flower that are typically brightly colored (usually to help attract pollinators to inconspicuous flowers).  The actual flowers of the plant are located at the ends of the stems, and are significantly smaller and less noticeable.  Look closely at the picture above, though, and you’ll see little green, red, and yellow clusters at the top of the plant; those are the flowers.

In the picture above we can see that the true flowers of the poinsettia are not the brightly colored leaves, but instead are these small green and red structures. The yellow things that look like lips are nectar glands, and the green balls with red filaments are the flowers (which are more appropriately termed pseudanthia or inflorescences, since they’re actually multiple flowers in a single structure). Let’s look at them closer:

This macro shot shows a number of red bracts surrounding the flowers and extending out of the frame. The green balls tipped with red are individual inflorescences called cyanthia, which are composed of multiple flowers surrounded by modified leaves¹. The green tissue surrounding each inflorescence is an involucre, a cluster of bracts (modified leaves) fused into a cup-shaped structure that contains multiple male flowers and one female flower within it.

Emerging from each involucre are red filaments supporting yellow anthers that are being grown by the male flowers (the anthers produce and release pollen).  A single female flower should be emerging from the center of each involucre, but isn’t easily visible in the picture.

The yellow liquid-filled structures attached to each involucre are nectar glands filled with nectar to attract pollinators.  On less-developed inflorescences the nectar glands look like little light-green lips.

If you’re in the Orange County area and want your own poinsettias to observe the flowers of, head to OCC this Friday and pick some up for yourself!  You’ll get a cool botanical specimen, and will be supporting a great program in the process. Oh yeah, and you’ll have a nice pretty plant for the holiday season.

[This is the first in a series of three posts; the second post is: Poinsettia flower closeups take two: getting even closer and the third is Poinsettia flowers part three: the female parts.]

¹ Yes, the plant works hard to hide its flowers. First there are dozens of large colorful bracts, and then smaller green ones. Sheesh!