Cyperus retrorsus - The Cylindric Sedge

 

Trinity River Audubon Center - July 26, 2013

When I first saw this plant at TRAC what caught my eye were the burr-like structures.  Taking a closer look revealed something unexpected - a triangular shaped stem - an identifying charactersitic of sedges.  As I was told by Ron Beecham, a professor of Biology here at the college, "Sedges have edges."

Here is a detailed look at the Cylindric Sedge (Cyperus retrorsus)



A photo from the field.  I have memories of running barefoot as a young boy and stepping on rather large cockleburs.  When I took a closer look what I found was not the stickery fruit of the cocklebur, but the typical, incomplete flower of a grass.

A photo from the field showing the flowers of the sedge.

I took a specimen back to the lab for more photos and for examination under the dissecting scope and the scanning electron microscope.

This photo shows the flowers of the sedge.  (Anyone familiar with the 3rd floor of the C Building at Eastfield College will probably recognize the patio where I took this photo.)  Also notice the three-part symmetry, typical of monocots.

In this photo you can see the multi-part flowers and even some of the anthers hanging out of the flowers. 

If you haven't studied botany, or have forgotten what you knew when you took it, it may seem a little confusing for me to use the term flower.  Where are the petals?  Lots of plants produce flowers without petals.  This includes most trees, grasses, and, in this case, sedges. 

 

Complete flowers contain all four of the major floral parts: sepals, petals, stamen -the male parts that produce the pollen, and the pistils or carples which contain the eggs.  We are most familiar with complete flowers and love their colorful, showy petals.  But there are also incomplete flowers which are missing one or more of the floral parts.  Grasses and trees often don't have petals, but they still reproduce sexually, just like those roses you may have given or received on special occasions.

 

A flower is the reproductive structure of a plant.  Some flowers contain both male and female reproductive structures on the same plant and are called monoecious (Greek for "one house").  Other flowers contain male or female structures on different plants are are said to be dioecious ("two houses").

This sedge has monecious, incomplete flowers.

Here is a closer look using the dissecting scope in the lab.

I brought the sedge back to the lab, put the stem in water and left it in the window over the weekend.  This little bug didn't seem to mind at all that the sedge was no longer outside.  It was happily crawling around and munching pollen.

Here you can get a sense of the structure of these flowers.  They are made up of overlapping segments with anthers and stigmas sticking out.  The white arrows in this picture indicate anthers.

 


Here is one section showing the structure. Each segment is a flower  and

has an anther and stigma and will produce a single seed.

The  next images were made with the scanning electron microscope. 

 

This structure is pretty small, only about 5 mm or about 1/4 inch long.  Each overlapping segment is a separate flower.

[40x]

 

At 200x you can see lots of details.  The anther has split open and spilled out its pollen and you can see the stigma.  (Unfortunately, the electron microscope dries out structures very quickly, so the pollen grains and cells of the stigma are collapsed.)  Even though these are the reproductive structures of the plant, they are still green and photosynthetic so they need to take in carbon dioxide and and release oxygen.  That is why you see stomata here. 

 

For this image I have turned the structure on its edge to show an anther hanging off.  These are actually visible with the naked eye and you can find them on the St. Augustine and Bermuda grass in your yard. [56x]

Same anther at 150x.  Here you can see it is split open and has pollen spilling out.

Several anthers at 190x.  Turns out it is very easy to cause these to fall off of the plant.  I shook the plant over my mounting stub to collect pollen and also found these. 

Anther with pollen at 300x.



Pollen grains at 1,700 x magnification.

The software on the scanning electron microscope allows me to make very precise measurements.  As shown in the image at 1,700x the pollen grain is only 22.61 microns x 29.90 microns.



I have to admit that I am very pleased with this image.  It shows the detail on a pollen grain at 5,000x magnification. 

Of course, the purpose of all of this structure is to make seeds.  Once the pollen falls on the stigma of the flower and fertilization occurs the seed will develop.

This image from the dissecting scope shows a couple developed seeds. Notice that the flowers are larger on the bottom of the structure because they develop first and are older.

I have pulled back the covering to show the seed underneath.  You can see the stigma still attached to the top of the seed.



The seeds on under the dissecting scope.  These are very small.  Notice the scale bar showing 500 microns or 1/2 mm.

65x magnification on the scanning electron microscope.  The total length of this seed is less than a millimeter.

Another seed for comparison. 

A close up of the attachment of the stigma to the seed.  350x

What about those triangular stems?  Here they are.

This is a cross section of the triangular stem.  Notice that the green, photosynthetic cells penetrate deeply into the stem.



Same view as above on the scanning electron microscope.  14x

Dissecting scope view of edge of stem.

Electron microscope view of stem edge. 230x

Electron microscope view of stem edge. 936x

 

More than 40 years ago my biology teacher at Borger High School, Mrs. Eve Wyles, taught me that you can always tell the cross-section of a monocot plant because the bundles of vascular tissue resemble monkey faces.  "Monocots have monkey faces."

 

This sedge is definitely a monocot.

 

Bundles of xylem and phloem,  monkey faces, indicated with arrows.  70x

More monkey faces.  130x

This one is for you, Mrs. Wyles.  450x

I really love going into the field each week and never know what will grab my interest.  I seem to learn something new every time.  Sedges?  Why not.

Please do not hesitate to contact me if you have comments or questions about this posting.  All images may be used, downloaded, or modified as long as you give credit to Eastfield College, Mesquite, TX. 

Murry Gans