Michael Peverett: Stemless grasses

Wednesday, July 16, 2025

Stemless grasses

Stemless bromes. Crowhurst, 3 July 2025.

A year later we did the family walk from Crowhurst Park holiday cabins to the Plough again.

Here's my post about it from last year:

https://michaelpeverett.blogspot.com/2024/07/crowhurst-fields.html

When we came out of the woods into the wheatfield, one of the first things I noticed were these peculiar stemless bromes. They were on the corner where the footpath turns south and runs down the middle of the field.

I suppose they are Soft Brome (Bromus hordeaceus), the most common of the short-awned annual bromes. There were masses of normal-looking specimens too, in fact they were growing all down the track, bordering the crop. But I only noticed the stemless ones on that first corner.

Something flashed in my brain and I took a couple of hasty photos while my family marched into the distance. If anyone had asked me then, I'd have supposed that the cause was environmental. Maybe the grasses on the corner were always being trampled or injured, or maybe they received a double dose of some chemical pollutant: pesticide or herbicide or fertiliser.... something like that must account for it, I thought.

But later, when I looked at the photos, I felt the stemlessness had to be genetic. A trampled or poisoned grass doesn't just go stemless.

I've never noticed stemlessness in grasses before, but I've seen it in other plants occasionally, such as Prickly Sow-thistle (Sonchus asper). The Dwarf Thistle (Cirsium acaule) reverses the normal course of things by being usually stemless, but sometimes stemmed.

But I had questions about a genetic explanation, too. The short-awned Bromes are annuals or biennials, so this patch of similar plants couldn't be explained as clonal perennation. On the other hand I've read that the anthers in Bromes are often not exserted, so self-pollination must be common; maybe that would account for a patch that all shared the same genetic feature.

Maybe stemlessness is normally disadvantageous (e.g. in terms of access to sunlight and wind) but in certain locations becomes advantageous. Such as on a regularly trampled corner, for instance.

I can't answer my questions, and so far I've failed to find anyone who knows about stemlessness in grasses, but I'll post this as a marker of unfinished business.