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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
