I confess that, despite my love of grasses, I have historically paid almost no attention to the rye-grasses, Lolium. Perhaps that is because Perennial Rye-grass Lolium perenne is such a ubiquitous species, appearing almost everywhere one cares to look. Whatever the reason, it is a genus I have largely overlooked.
Recently, however, I began noticing a few odd-looking plants in my local park here in Newcastle, prompting me to take a closer look. As is so often the case, what initially seemed unremarkable turned out to be rather more interesting than expected. So, with a hand lens in hand, I decided to dig a little deeper, starting with…
Perennial Rye-grass Lolium perenne
Perennial Rye-grass Lolium perenne is one of our most abundant grass species, occurring in almost every kind of grassland imaginable: hay meadows, chalk downland, rush pastures, wet grasslands, lawns, road verges and amenity grassland. It is particularly associated with improved grasslands and areas treated with inorganic fertilisers, making it a familiar sight in urban environments. According to the BSBI, L. perenne was probably once primarily a species of wet grasslands on heavy soils, from which several forms were selected and bred during the early nineteenth century. Whatever its origins, it has long since escaped the confines of its natural habitat and is now virtually ubiquitous.
Fortunately, it is a relatively straightforward species to identify. The flowers are arranged in a long, narrow, wiry spike, with the spikelets alternating from side to side along a slightly sinuous central stem. Unlike the superficially similar couch grasses Elymus spp., the flat face of each spikelet is held edge-on to the stem rather than facing it. It also typically lacks the awns of other rye-grasses that we’ll come to in a moment.
The plants illustrated below were growing on a small patch of grassland in the aforementioned park.
Italian Rye-grass Lolium multiflorum
Italian Rye-grass Lolium multiflorum is a species I encounter far less frequently in my part of the world, though it remains reasonably common. An annual or short-lived perennial, it is most often associated with re-seeded grassland, but also turns up on field margins, in gateways, along farm tracks, beside roads and on other areas of disturbed ground. It frequently occurs as a relic of sowing and is also a regular bird-seed alien, its seeds arriving as contaminants in grain mixes. Interestingly, it is not a particularly strong competitor and rarely persists for long in established grassland, instead appearing to undergo a series of boom-and-bust cycles dependent on repeated introductions.
At first glance, L. multiflorum looks very similar to L. perenne. Traditionally, the easiest way to distinguish the two is by the presence of conspicuous awns on the lemmas, often reaching 10 mm or more in length. As we shall see, however, things are not always quite so straightforward.
For reference, the plants illustrated below are good examples of L. multiflorum: one growing conveniently beneath a set of bird feeders and the others occurring on an area of disturbed ground in the park.
Hybrid Rye-grass Lolium × boucheanum
This is where things start to become a little confusing.
Exploring the park, there was certainly no shortage of Perennial Rye-grass Lolium perenne, while several convincing examples of Italian Rye-grass L. multiflorum could be found on disturbed ground associated with recent earthworks. Looking more closely, however, some plants seemed to fall awkwardly between the two.
The most obvious difference lay in the awns. Rather than bearing the long, conspicuous awns expected of a typical L. multiflorum, some plants possessed awns of varying lengths, noticeably shorter than those of the “good” Italian Rye-grasses growing nearby. Furthermore, comparing spikelets on the same plant revealed a mixture of forms: some lemmas carried distinct awns, while others were completely awnless. This pattern was repeated throughout the inflorescence.
Consulting the helpful BSBI crib sheet, this combination of characters appeared to point towards Lolium × boucheanum, the hybrid between Perennial and Italian Rye-grass. The hybrid is described as having short awns of variable length, with some lemmas lacking awns altogether, and generally displaying an appearance intermediate between its parents. On paper, at least, my plants seemed to fit the bill rather well.
While both rye-grass species and their hybrid are relatively common, Lolium × boucheanum is undoubtedly under-recorded, and this represents the first time I have knowingly encountered a convincing example. Perhaps the lesson here is simply that I have not been looking closely enough.
Whatever the case, it has certainly encouraged me to pay more attention to rye-grasses in future. As so often happens in botany, the commonest plants can prove surprisingly interesting once examined in a little more detail. Even a genus I had long dismissed as rather mundane turned out to have a few surprises in store.
The final image below illustrates a particularly nice series of plants showing a gradual transition from Lolium × boucheanum towards L. multiflorum, neatly demonstrating just how blurred the boundaries between these taxa can appear in the field.
