Saturday, October 3, 2020

Meet the strange shimmering spikelets of Schizachyrium scoparium (Little Bluestem)

When an observer looks at the seedheads of Schizachyrium scoparium (Little Bluestem), they may gasp at its beauty, and marvel at the whitish fluff that decorate the reddish main axis of the inflorescence. But little do they know what a complex piece of biological engineering that whitish fluff is when viewed at the macro level. 

As many of the Orang Poa (Grass People) know, the unit of reproduction in grasses is the spikelet. The spikelet contains the florets ("flowers") of the grass, and of course the florets (like any flower) contain the stamens (male) and pistils (female). 

In the case of S. scoparium, the spikelets form a complex little unit with many parts. 

Pairs of spikelets run along the axis of the raceme of the inflorescence. Each pair is composed of 2 spikelets (see image below).

The smaller spikelet in the pair sits on top of a pedicel, and is rudimentary and hairy. The larger and fertile spikelet is sessile, with two structures called glumes completely covering the two florets inside. One of the florets is sterile, while the fertile floret has a long bent awn that extends from its central nerve and extends out of the glumes.  You can see the bent awn of the fertile floret in the image below, but the rest of the floret is hidden inside the enclosing glumes.

The unit of dispersal is composed of the two spikelets, in addition to a short segment of the raceme axis. An abscission layer below the axis segment allows the seed-carrying unit to disarticulate from the raceme, and the hairs on the rudimentary spikelet and the axis segment allow it to be carried by the wind for very short distances (typically less than 2 meters from the mother plant).

As I watched, one of the "seeds" floated onto the ground and I took pics of it before the wind could blow it away (see image above). 

(B) is the bent awn of the fertile floret that is being hidden between the enclosing glumes, and (A) is the rudimentary spikelet which sits on a pedicel. The axis segment that connected the unit to the next spikelet pair is labeled (C), and you can see at the top where it was detached from the raceme.

So the next time you see seedheads of S. scoparium, just remember how such simple looking structures actually are composed of wonderfully intricate parts! 



  1. Replies
    1. Thanks! I was surprised at how complicated that "fluff" really was. Lots of interesting things going on below the level of our normal vision.

  2. Great post. Very excellent description of flowering detail.

    1. Thanks! It was interesting for me to find out the details as well. What a remarkable plant.

  3. Thank you for this - I was finally able to "see" the S. scoparium among the similar (to me, at least) Andropogon virginicus.

    1. Thanks for pointing out A. virginicus! From what I can see, the overall coloring of the mature plants are different, the seedheads of A. virginicus have this hood-like bract/cover, and the awns on its spikelet are relatively straight (as opposed to bent as in S. scoparium).