best distinctions are found in the position of the embryo in
relation to the endosperm—lateral in grasses, basal in Cyperaceae—and
in the possession by Gramineae of the 2-nerved palea
below each flower. Less absolute characters, but generally
trustworthy and more easily observed, are the feathery stigmas,
the always distichous arrangement of the glumes, the usual
absence of more general bracts in the inflorescence, the split
leaf-sheaths, and the hollow, cylindrical, jointed culms—some
or all of which are wanting in all Cyperaceae. The same characters
will distinguish grasses from the other glumiferous orders,
Restiaceae, and Eriocaulonaceae, which are besides further
removed by their capsular fruit and pendulous ovules. To other
monocotyledonous families the resemblances are merely of
adaptive or vegetative characters. Some Commelinaceae and
Marantaceae approach grasses in foliage; the leaves of Allium,
&c., possess a ligule; the habit of some palms reminds one of
the bamboos; and Juncaceae and a few Liliaceae possess an
inconspicuous scarious perianth. There are about 300 genera
containing about 3500 well-defined species.
The great uniformity among the very numerous species of this vast family renders its classification very difficult. The difficulty has been increased by the confusion resulting from the multiplication of genera founded on slight characters, and from the description (in consequence of their wide distribution) of identical plants under several different genera.
No characters for main divisions can be obtained from the flower proper or fruit (with the exception of the character of the hilum), and it has therefore been found necessary to trust to characters derived from the usually less important inflorescence and bracts.
Robert Brown suggested two primary divisions—Paniceae and Poaceae, according to the position of the most perfect flower in the spikelet; this is the upper (apparently) terminal one in the first, whilst in the second it occupies the lower position, the more imperfect ones (if any) being above it. Munro supplemented this by another character easier of verification, and of even greater constancy, in the articulation of the pedicel in the Paniceae immediately below the glumes; whilst in Poaceae this does not occur, but the axis of the spikelet frequently articulates above the pair of empty basal glumes. Neither of these great divisions will well accommodate certain genera allied to Phalaris, for which Brown proposed tentatively a third group (since named Phalarideae); this, or at least the greater part of it, is placed by Bentham under the Poaceae.
The following arrangement has been proposed by Professor Eduard Hackel in his recent monograph on the order.
A. Spikelets one-flowered, rarely two-flowered as in Zea, falling from the pedicel entire or with certain joints of the rachis at maturity. Rachilla not produced beyond the flowers.
a. Hilum a point; spikelets not laterally compressed.
α Fertile glume and pale hyaline; empty glumes thick, membranous to coriaceous or cartilaginous, the lowest the largest. Rachis generally jointed and breaking up when mature.
1. Spikelets unisexual, male and female in separate inflorescences or on different parts of the same inflorescence. 1. Maydeae.
2. Spikelets bisexual, or male and bisexual, each male standing close to a bisexual.2. Andropogoneae.
β Fertile glume and pale cartilaginous, coriaceous or papery; empty glumes more delicate, usually herbaceous, the lowest usually smallest. Spikelets falling singly from the unjointed rachis of the spike or the ultimate branches of the panicle. 3. Paniceae.
b. Hilum a line; spikelets laterally compressed. 4. Oryzeae.
B. Spikelets one- to indefinite-flowered; in the one-flowered the rachilla frequently produced beyond the flower; rachilla generally jointed above the empty glumes, which remain after the fruiting glumes have fallen. When more than one-flowered, distinct internodes are developed between the flowers.
a. Culm herbaceous, annual; leaf-blade sessile, and not jointed to the sheath.
α Spikelets upon distinct pedicels and arranged in panicles or racemes.
I. Spikelets one-flowered.
i. Empty glumes 4. 5. Phalarideae.
ii. Empty glumes 2. 6. Agrostideae.
II. Spikelets more than one-flowered.
i. Fertile glumes generally shorter than the empty glumes, usually with a bent awn on the back. 7. Aveneae.
ii. Fertile glumes generally longer than the empty, unawned or with a straight, terminal awn. 9. Festuceae.
β Spikelets crowded in two close rows, forming a one-sided spike or raceme with a continuous (not jointed) rachis. 8. Chlorideae.
γ Spikelets in two opposite rows forming an equal-sided spike. 10. Hordeae.
b. Culm woody, at any rate at the base, leaf-blade jointed to the sheath, often with a short, slender petiole. 11. Bambuseae.
Tribe 1. Maydeae (7 genera in the warmer parts of the earth). Zea Mays (maize, q.v., or Indian corn) (q.v.). Tripsacum, 2 or 3 species in subtropical America north of the equator; Tr. dactyloides (gama grass) extends northwards to Illinois and Connecticut; it is used for fodder and as an ornamental plant. Coix Lacryma-Jobi (Job’s tears) q.v.
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| Fig. 18.—A pair of spikelets of Andropogon. |
Tribe 2. Andropogoneae (25 genera, mainly tropical). The spikelets are arranged in spike-like racemes, generally in pairs consisting of a sessile and stalked spikelet at each joint of the rachis (fig. 18). Many are savanna grasses, in various parts of the tropics, for instance the large genus Andropogon, Elionurus and others. Saccharum officinarum (sugar-cane) (q.v.). Sorghum, an important tropical cereal known as black millet or durra (q.v.). Miscanthus and Erianthus, nearly allied to Saccharum, are tall reed-like grasses, with large silky flower-panicles, which are grown for ornament. Imperata, another ally, is a widespread tropical genus; one species I. arundinacea is the principal grass of the alang-alang fields in the Malay Archipelago; it is used for thatch. Vossia, an aquatic grass, often floating, is found in western India and tropical Africa. In the swampy lands of the upper Nile it forms, along with a species of Saccharum, huge floating grass barriers. Elionurus, a widespread savanna grass in tropical and subtropical America, and also in the tropics of the old world, is rejected by cattle probably on account of its aromatic character, the spikelets having a strong balsam-like smell. Other aromatic members are Andropogon Nardus, a native of India, but also cultivated, the rhizome, leaves and especially the spikelets of which contain a volatile oil, which on distillation yields the citronella oil of commerce. A closely allied species, A. Schoenanthus (lemon-grass), yields lemon-grass oil; a variety is used by the negroes in western Africa for haemorrhage. Other species of the same genus are used as stimulants and cosmetics in various parts of the tropics. The species of Heteropogon, a cosmopolitan genus in the warmer parts of the world, have strongly awned spikelets. Themeda Forskalii, which occurs from the Mediterranean region to South Africa and Tasmania, is the kangaroo grass of Australia, where, as in South Africa, it often covers wide tracts.
Tribe 3. Paniceae (about 25 genera, tropical to subtropical; a few temperate), a second flower, generally male, rarely hermaphrodite, is often present below the fertile flower. Paspalum, is a large tropical genus, most abundant in America, especially on the pampas and campos; many species are good forage plants, and the grain is sometimes used for food. Amphicarpum, native in the south-eastern United States, has fertile cleistogamous spikelets on filiform runners at the base of the culm, those on the terminal panicle are sterile. Panicum, a very polymorphic genus, and one of the largest in the order, is widely spread in all warm countries; together with species of Paspalum they form good forage grasses in the South American savannas and campos. Panicum Crus-galli is a polymorphic cosmopolitan grass, which is often grown for fodder; in one form (P. frumentaceum) it is cultivated in India for its grain. P. plicatum, with broad folded leaves, is an ornamental greenhouse grass. P. miliaceum is millet (q.v.), and P. altissimum, Guinea grass. In the closely allied genus Digitaria, which is sometimes regarded as a section of Panicum, the lowest barren glume is reduced to a point; D. sanguinalis is a very widespread grass, in Bohemia it is cultivated as a food-grain; it is also the crab-grass of the southern United States, where it is used for fodder.
In Setaria and allied genera the spikelet is subtended by an involucre of bristles or spines which represent sterile branches of the inflorescence. Setaria italica, Hungarian grass, is extensively grown as a food-grain both in China and Japan, parts of India and western Asia, as well as in Europe, where its culture dates from prehistoric times; it is found in considerable quantity in the lake dwellings of the Stone age.
In Cenchrus the bristles unite to form a tough spiny capsule
