The most hated wildflowers?

Trampled, poisoned and mown to the ground. Are these the most hated wildflowers?

Grasses and their allies

David Beeson

Delicately waving in the summer’s breeze, their leaves capturing the sun’s donated energy and using an alchemy to weave it into chemical bonds that trap the Kilojoules (Calories) into a usable form, grasses have a vital role. Without the tamed grasses human nutrition and agriculture would be quite different. No cows, no cow’s milk, no beef, no sheep, no cheese … the list goes on. The grasses of the Fertile Crescent around the Rivers Tigris and Euphrates jump-started the agricultural revolution that gave humans the food resources and time to produce towns, cites, development and culture. Without the taming of grasses we would have no wheat, barley, rye, rice, sweetcorn or oats in the fields today. No bread, no pizza, no pasta, no beer, no rice pudding. No bamboo canes for the garden.

Grasses may lack the gleaming colours of yellow flag iris, red ragged robin, blue cornflowers and the white of wild carrot, yet they have a unique beauty of their own.

Even as a biologist I seldom spend the time to seek out the splendour of their wind-pollinated flowers with their feathery stigmas and their huge, mobile anthers. I do not invest the time to explore their oat-coloured flower parts that are so divergent from their showier cousins. Even in fruit they have a stunning form that flower-arrangers appreciate more than wildlife enthusiasts.

With growth points, nodes, not at the tips of their growing points, these forgotten flowering plants (Angiosperms) can take grazing when others would wither away. In the hottest, driest and combustible of UK summers they may shudder and retreat but, given a burst of rainfall will pop up again, making no complaint, and just get on with life. Not so the most beautiful of roses or orchids who would sulk and wither away, never to be seen again.

They are common and diverse. Even UK commercial seed mixes are said to contain up to 100 different grass species. Around the world there are over 11000 different species. Yet I mostly ignore them. Do you? Is that fair?

A typical grass:

Grasses? Well, most of us confuse grasses, sedges and rushes. They all look relatively similar … green, often long leaved and with comparatively non-showy flowers. They are plants with parallel leaf veins (Monocotyledonous plants – plants with a single seed leaf) as opposed to plants that have spreading (netted / reticulated) leaf veins (Dicotyledonous plants – with two seed leaves). They are wind pollinated so have no need to offer nectar, pollen and a showy exterior to attract pollinators. Growing in masses they use the wind to effectively spread their pollen DNA.

Most grasses are hollow stemmed, prefer well-drained, dryish conditions and full sun, whereas most sedges and rushes like it moist.

Grasses have small flowers (florets) enclosed by a pair of scales (glumes) and are grouped together into spikelets. Their leaves are arranged alternately forming two ranks.

A single grass flower:

Sedge stems are solid, not hollow, and usually triangular in cross section. Their leaves are arranged spirally in three ranks. Sedge flowers are wind-pollinated with small, often brown or black male and female flowers being borne on the same plants. Some sedges will thrive in fairly deep shade.

A typical sedge:

The stems of rushes are round in cross section, with solid or pithy, but not three-sided, stems and in many species the leaves are reduced to sheaths around the base of the plant. The bract around the flower can look like a continuation of the stem, so flowers appear to stick out of the side of stems. These flowers have a more conventional form with six ‘petals’.

A leafy rush:

A more locally common rush:

Soft and hard rushes, like the above, are common on local wetlands.
 GrassesSedgesRushes
StemHollowSolidSolid or pithy
Shape of flower stalksRoundTriangularRound
LeavesCan be along
flower stem
Mostly basalMostly basal
NodesAlong flower stem
and ground level
Not
visible
Along flower stem,
but less visible

Grasses are found in virtually any habitat, with float (flote) grass (Glyceria fluitans) even being found growing in my own pond and in ditches or shallow ponds. However, they mostly prefer drier conditions.

For rushes and sedges it is best to look in moist meadows, although the glaucous sedge (Carex flacca)) is found on even dry chalky hillsides.

These grasses, sedges and rushes are important organisms. From the icy tundra, to the tropics, the mountain tops, to seaside sand dunes and even in the depths of a forest you will encounter them. They support the grazing animals on the American plains, the kudu and impala on the savanna and the rabbits on my lawn. And they keep on surviving despite all the nibbling, burning and trampling. Impressive!

Grasses are even fashionable in the UK ornamental garden. Stipa gigantica, a beautiful 1.5m high grass, is a star in my own garden and many other species join it in delighting gardeners in high summer.

Stipa gigantica in a flowerbed

Marram grass and lyme grass hold sand dunes together, allowing them to stabilize and hold back the sea, while reeds clean water of pollution and provide a habitat for numerous types of birds and made the roofs of ancient people’s dwellings.  

Why are they hated?

Well, it is mainly by tidy gardeners who want stripes on their lawn and their grasses cut to within a millimetre of their survival. They hate them growing too tall and how dare they try to flower!. And, should they think to encroach on their ‘flower’ beds then the glyphosate will surely be there in a moment. The farmer may enjoy some wild grass species, but only if they grow rapidly and feed their cattle, sheep or horses, the rest are killed and replaced by rye grass.

But they are mostly ignored by us – the wildlife enthusiasts. So, we must mend our ways! Look out for the delightful quaking grasses on the chalky downs, wood medick in woods and shady places, wall barley on waste ground, cocksfoot in which harvest mice love to nest and the fine-leaved fescues. Once these are recognised it is easier to explore the other grasses, sedges and rushes.

While you are there … why do grasses stay small? Oak trees and redwoods can be huge, yet grasses never reach that size.

Cross section of a grass stem. Note the vascular bundles are spread and NOT in a single organised ring
Sunflower, but a young tree section would be similar. Here a single ring of vascular tissue is developing.

The upper diagram is a cross section (TS Monocot)of a grass stem. The lower a sunflower, but could be a young redwood tree (TS dicot). The critical spot to look is for the location of the vascular bundles – these contain the phloem (organic and mineral transport), the xylem (water and other mineral transport) and between them the growth region for new phloem and xylem – the cambium (meristem).

Xylem are the big red cells. Phloem the greenish cells below the phloem fibres and the cambium miniscule green-stained cells between the two. Red staining shows woody cells, green staining non-woody cells. Phloem fibres are not transport cells but provide mechanical support to the stem. (The staining on this slide is not perfect! Someone used too much red stain.) The pith is towards the centre of the stem.

With the sunflower growth in the cambium allows the girth of the stem to increase and leaves the xylem (wood) on the inside, with the phloem (soft, non-woody cells) being crushed to the outside. Similar growth in the grass results in chaos and a woody core never properly develops – so no chance of a structure that supports high growth. Grasses remain small and their upright stems seldom last for long.

But, why would the grasses care? They do not. Their strategy, and it is a successful one, is to remain small and live alongside the grazers by having their growth points out of the reach of most herbivorous teeth. For a similar reason they do not fill themselves full of metabolically expensive toxins, using their resources instead to quickly regrow after being partly eaten. However, some grasses are rich in silica that discourages too much grazing. The silica is taken up from the soil.

As innocuous as they may look, some grasses are well defended mechanically.

From – http://www.indefenseofplants.com/blog/2016/9/25/grass-defenses

What (below) looks like the mouth of a shark is actually the edge of a blade of grass. It is covered in microscopic, razor-sharp daggers. The daggers themselves are specialized structures called “phytoliths.” Grasses can manufacture phytoliths from silica that they absorb from the soil. Not all species produce these daggers. Some distribute phytoliths throughout their leaves, essentially packing themselves with tiny granules of glass. Their presence is an adaptation against being grazed. 

It’s not hard to imagine how effective silica daggers can be. Run your finger along the stem or leaves of one of these grasses and you are likely to draw blood. Early US settlers coined the term “ripgut grass” because the bellies of horses and other livestock would get seriously lacerated from running through it. Whereas this defense is rather straight forward, the other types of phytoliths are a little more subtle in their effectiveness. 

Silica is tough and chewing on leaves chock full of it can do a real damage to teeth. That is the main reason why the teeth of many grass grazers alive today grow continuously. If their teeth were like ours, the phytoliths within the blades of grass would wear them down to useless nubs. In fact, the evolution of phytoliths in grass is thought to have ushered in a new age of grazing mammals via the extinction of those that could not cope with these microscopic defences. 

OLYMPUS DIGITAL CAMERA

It’s not just about teeth either. Insects feeding on blades of grass may be able to get past the phytoliths without an issue, but the story changes once it makes it to the gut. Silica particles have been shown to interfere with digestion. Caterpillars feeding on grasses containing high amounts of silica in their leaves had decreased levels of digestion efficiency, which resulted in reduced growth rates.

Freshwater Habitats

On a different track, I’ve just come across a new organization (to me) – https://freshwaterhabitats.org.uk/ . Might be worth checking out.

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