Grass and Grassland - Ian Moore

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Base of leaf-sheath white; blades dull, somewhathairy. White creeping stems below ground. Agropyron repens 9 Plant short-lived, old leaf-sheaths not persisting. Lolium multiflorum Plant perennial, old dead leaf-sheaths present atbase. 10 10 Plant small, smooth, auricles not fringed. Festuca pratensis Plant large, harsh, auricles fringed. Festuca arundinacea 11 Plant tufted or only slightly spreading. 12 Plant strongly creeping. Agrostis sp. 12 Leaves without hairs. 13 Leaves hairy. 14 13 Shoot base bulbous, pale, ligule short, pointed. Phleum pratense Shoot base not swollen, old sheaths dark brown, liguleblunt. Alopecurus pratensis 14 Sheath not split. Bromus mollis Sheath split. 15 15 Veins of sheath red. Holcus lanatus Veins of sheath not red. 16 16 Hairs scattered, blade very long, roots yellow. Arrhenatherum elatius Hairs on sheath pointing down. Trisetum flavescens Conspicuous tuft of hairs at top of sheath. Anthoxanthum odoratum 17 Sheath split; plant tufted. Festuca ovina Sheath not split; plant usually creeping. Festuca rubra spp. rubra

      The inflorescence varies widely in the different genera and, if present, is the easiest means of identification. It is made up of a varying number of “partial” inflorescences called spikelets, each of which is composed of one or more flowers, each with two enveloping protective structures, the lemma and the palea. In most cases the grass flowers bear both stamens and pistil but in maize (Zea mays), for instance, the male flower is produced in the “tassel” and the female on the “cob” with its greatly thickened axis. Very rarely male and female flowers may be borne on different plants, as in buffalo grass (Buchloe dactyloides). The form of inflorescence is determined according to the way spikelets are arranged on the stem. The spikelets may be borne directly on the main axis to form a spike as in the ryegrass or couch grass; they may be borne on simple branches to give a raceme, as in false brome (Brachypodium spp.), or, as in the majority of grasses, borne on secondary, tertiary or even more sub-divided branches to give a panicle. The length and stoutness of the branches provide a wide variety of panicles between the extremes of an erect, close inflorescence, superficially resembling a spike, as in foxtail (Alopecurus spp.) or timothy, and one which is long and drooping, loose and spreading, like the bromes.

      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

1 Inflorescence a spike; spikelets not stalked. 2
Inflorescence a raceme. One very shortly-stalked,many-flowered spikelet at each node. Brachypodium spp.
Inflorescence a panicle (spikelets on long or shortbranched stalks). 7
2 Spike branched. Spartina spp.
Spike not branched. 3
3 One spikelet at each node. 4
Two spikelets at each node. Spike large, spikeletsseveral-flowered. Elymus arenarius

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