Ian Moore - Grass and Grassland

Flowering usually takes place from May to July, although in mild winters a number of species develop flower-heads in December or even January. Annual meadow grass, on the other hand, can generally be seen in bloom throughout the year. The first grass to flower in the spring is holy grass ( Hierochloë odorata ), which is in bloom about the end of March, but this species is very rare in the British Isles, and is confined to three Scottish counties and one Irish. Meadow foxtail ( Alopecurus pratensis ) and sweet vernal grass may flower in April, the ryegrasses in May, cocksfoot and the fescues in June, and timothy in July. Woodland and mountain species are somewhat later in flowering than species of the same genera growing in more open habitats or at lower altitudes. The early-flowering grasses are usually those in which only a comparatively short day is required for flower initiation; the later are those needing a longer day.

Since the actual flowers of grasses are very simple and show comparatively little variation, classification and identification have to depend largely on the structure and arrangement of the spikelets. Each true flower consists only of a single pistil with (usually) two styles, and (usually) three stamens, plus, in most grasses, a pair of minute scales which are known as “lodicules” and which have been regarded as representing very reduced sepals. Each flower is protected by two much larger structures, the inner, usually two-keeled, palea and the round, single-keeled, lemma. The lemma and palea fit closely together over the flower and are only separated for a short time when the lodicules swell up temporarily, pressing them apart, and allowing the styles and stamens to protrude and wind-pollination to take place.

Each true flower plus its lemma and palea is known as a “floret” and the spikelet consists of from one to about twenty florets. At its base there are two (occasionally one or none) protective structures, the glumes. Both the lemmas and the glumes may be furnished with bristles (awns), which are useful features for identification.

The following key will enable the more important species to be identified in the flowering stage.

KEY FOR IDENTIFICATION OF COMMON GRASSES WHEN IN FLOWER

Grasses show an amazing tolerance to external conditions. For instance sheep’s fescue, which grows down to sea level in this country, has also been recorded on the highest mountains in Britain and at nearly 18,000 ft. in the Himalayas. Then again, many grasses from low-lying habitats in temperate regions adapt themselves to high altitudes in tropical countries. Others survive wide differences of climate, the classic example of adaptability being perhaps sweet vernal grass, which flourishes from sea level to above the snow line, is equally at home on sand, loam or clay, and is found in many countries of the world with vastly different climates, ranging from North Africa to Siberia.