Grass Types (Grass, Bunch Grass, Single-Stem Grass, Rush, Sedge)

 

What’s a grass?  In PlantID.net, grasses include “true grasses”, sedges and rushes.  If it looks like a grass, we call it a grass.

 

There are four types of grasses that are often easy to distinguish.  We use grass type in searches, so they’re useful for you to know.

 

Bunch Grasses have grass spikelets and grow from a single root crown. They look bunchy.

Tall Melica (Melica frutescens)

Photo by Keir Morse

Single-Stem Grasses also have grass spikelets  but each stem grows from its own root, or in colonies connected by stolons and rhizomes. 


Beardless Wild Rye (Elymus triticoides)

Photo by Ron Vanderhoff

Rushes are round – round stems and clusters of tiny 6-part flowers.


Green Headed Rush (Juncus chlorocephalus)

Photo by Steve Matson

 

Sedges have edges – triangular stems and tiny, scaly florets.

Blackish Sedge (Carex subnigricans)

Photo by Steve Matson

 

 

This is a good first understanding of grass types and it’s fine to stop here if you like.  But there is more to learn if you have the appetite. 

 

 

Bunch Grasses and Single-Stem Grasses are “true grasses”.  They have several distinguishing characteristics.

·        Cylindrical, hollow stems, like straws, connect with solid nodes (knobby knees).  (Like so many other generalizations, this is only mostly true.  Dallis Grass, for instance, sometimes has solid stems.)

·        Grass Leaves look like what you’d expect (see more in Grass Leaves).

·        True grasses have distinctive spikelets, made up of one-to-many florets, growing out of 2 glumes.

 

Hollow stems connect with solid nodes (knobby knees).

Smooth Brome (Bromus racemosus)

Photo by Zoya Akulova-Barlow

Grass leaves have several parts.


Bolander’s Reedgrass(Calamgrostis bolanderi)

Photo by Zoya Akulova-Barlow

This spikelet has 2 florets inside 2 glumes

Slender Wild Oats – photo by Wilde Legard

This spikelet has 12 florets with 2 glumes at the base.

Rattlesnake Grass – photo by Wilde Legard

 

Bunch and single-stem grass stems are formed differently

 

A grass can grow new stems in a couple of ways.

 


Diagram from wikiwand.com/simple/Grass

 

One way is to grow many stems from the crown at the top of a root ball.  These extra stems are called tillers.  Grasses that expand this way are called bunch grasses.

 

Another way is to grow sideways shoots (stems) just above or below the ground (stolons or rhizomes).  These shoots can grow new vertical stems and roots at their nodes.  Grasses that expand this way are called single-stem grasses.  They may grow close together, but they don’t all crowd down to a single root crown, so they don’t look as bunchy.

 

 

Rushes and Sedges are grass-like, but different.

 

Rushes have round, solid stems, often with no noticeable leaves.  Their tiny, six-part flowers start green and often turn tan or brown.  Flowers form in clusters either at the top of the stem or, apparently, on the side of the stem.

 


Baltic Rush – photo by Steve Matson


Baltic Rush – photo by Wilde Legard

 

Actually, what looks like a stem above the flower cluster is not a stem but a bract. 

 

Rush leaf blades can be inrolled, sometimes forming cylinders.  Other blades can be flat, lying next to each other like iris leaves.  Others have only leaf sheaths and no blade at all. 

 


Mariposa Rush (Juncus dubius)

Photo by Keir Morse


Sickle Leafed Rush (Juncus falcatus)

Photo by Neal Kramer


Pacific Rush (Juncus effusus)

Photo by Neal Kramer

 

 

 

We have two genera of rushes in California, and they’re pretty easy to distinguish.  Here’s more on rushes.

 

 

Most sedges have edges.  If you run your hand along the stem you’ll feel that it’s triangular, with three flat edges running the length of the stem.  You’ll almost always find sedges near or in water.  Sedges often have long, narrow leaves, typically starting at the bottom of the plant.

 


Bracted Sedge – photo by Steve Matson


Bracted Sedge – photo by Keir Morse

 

Sedges have separate male and female florets in the same inflorescence.  Above, you can see female florets, protected inside a smooth coating, underneath male florets with stamens sticking out.

 

There are several genera of sedges (some without triangular stems).  They’re pretty easy to distinguish.  Here’s more on sedges.

 

 

 

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