Sweet-grasses
What are they?
The Sweet-grasses are a small group of plants that are mostly rather similar to each and similar in their habitat requirements. They often produce lush, rich green, foliage and stems with a sweet flavour that gives them their name and they are favoured by livestock when grazing in freshwater marshland habitats.
Where are they found?
These are plants of freshwater wetland habitats, ranging from permanent wetlands such as river and lake margins, to temporarily wet or damp places (usually winter-wet) such as hollows in woodland and even rutted tracks across damp ground in grazing marshes.
Identification
Click here for help with some of the terminology used on the grass pages. The smaller sweet-grasses can be distinguished as a group by their lush green colour and their long. strap-like leaves, typically with keeled sheaths. The flower spikes are long, narrow and arching with short side branches. The florets appear in narrowly cylindrical spikelets with the glumes typically strongly overlapping each other. Reed Sweet-grass has a similar look to its spikelets, but they are arranged in a larger, multi-branched and more or less upright spike. Identifying the smaller species can be difficult and requires careful attention to the lemmas and the use of a ruler for measurement of the flower parts.
Reed Sweet-grass Glyceria maxima
A native perennial, common along the margins of rivers, lakes and ponds. Flowers June to August. Plants 90-250cm in height with strong, creeping rhizomes that can produce extensive, single-species stands. Leaf blades 7-20mm wide, bright green, hairless, flat and abruptly pointed at the tip. Leaf sheaths rounded towards their base, keeled towards the leaf blade, smooth. Ligule membranous but quite stiff, 3-6mm long. Flower spike feathery when young, spreading at anthesis; typically carried well above the leaves on upright stems. Spikelets 5-12mm, oblong to narrowly oblong, slightly compressed, with 4-10 florets. Glumes broadly ovate, membranous. Lemmas 3-4mm long, rounded on the back, obtuse at the tip and having 7 prominent veins. The large size and upright flower spikes with spreading branches readily distinguishes this species from the other sweet-grasses.
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Floating Sweet-grass Glyceria fluitans
A native perennial, common along the margins of rivers, lakes and ponds as well as in seasonally wet grazing marsh and low-lying ground. Flowers May to August. Plants to 100cm in height but often much less and typically forming creeping mats that spread out onto the surface of open water. Leaf blades 3-10mm wide, green, hairless, flat and abruptly pointed at the tip, flat or folded along the midrib. Leaf sheaths hairless, smooth, often purple-tinted. Ligule membranous, 5-15mm long. Flower spike 10-54cm long, typically forming a slender, wand-like panicle, the branches spreading at anthesis and later closing together. Spikelets 18-35mm, narrowly oblong, slightly compressed, with 8-16 florets. Glumes oblong or elliptic-oblong, membranous. Lemmas 5.5-6.5mm long, rounded on the back, distinctly narrowed towards the tip and having 7 prominent veins; overlapping broadly at first, but later curling in at the margins.
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Small Sweet-grass Glyceria declinata
A native perennial, widespread but less common than the other species and most likely to be found in small farm ponds or along ditchsides, often where these dry out in the summer. Flowers June to September. Plants to around 60cm in height but often much less and forming small tufts or loose patches. Leaf blades 3-14mm wide, green, or often greyish-green, hairless but often rough on the margins and pointed at the tip, flat or folded along the midrib. Leaf sheaths keeled, hairless or minutely hairy. Ligule membranous, 2-8mm long. Flower spike 10-45cm long, typically forming a slender, wand-like panicle, with a few, short branches towards the base. Spikelets 10-25mm, narrowly oblong, cylindrical but becoming slightly compressed, with 7-16 florets. Glumes persistent, oblong or elliptic-oblong, membranous. Lemmas 3.5-5mm long, rounded on the back, broadly elliptical and slightly three-lobed, with 7 prominent veins; overlapping broadly at first, but later curling in at the margins. The broad lemmas with a three-lobed tip are a good way to tell this species from Floating Sweet-grass.
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