TIE GRASSES OF CENTRAL AMERICA By A. S. Hitchcock INTRODUCTION Until the present century very few collections of plants were made in Central America and until recently little has been written on the grasses of that region. Panama was visited by some of the earlier expeditions sent out to study the flora of divers parts of the world. Among these was the voyage of the Herald. Seamann's account of the botany of this voyage included a flora of the Isthmus of Panama. The Biologia Centrali-Americana by Godman and Salvin included an account of the botany by Hemsley. In this work there are no detailed descriptions, and the grasses listed are mainly from Mexico. The collections of Heyde and Lux, of Thieme, and of John Don- nell Smith in Guatemala, and of Pittier and his colleagues in Costa Bica, yielded many grasses. Hackel described many new species from these collections, and a smaller number were described by Vasey and by Scribner. Various parts of Central America have been visited during the present century by American botanists. Of special im- portance, aside from the collections mentioned above, are those made by Paul C. Standley, who visited Panama, Costa Rica, El Salvador, and Honduras. Mr. Standley has published a part of the results of his explorations in Central America in his account of the Flora of the Panama Canal Zone.1 The writer visited Panama, Costa Rica, Nicaragua, El Salvador, Honduras, and Guatemala, in 1911, collect- ing only grasses. The collections now in the United States National Herbarium are large and may be said to be fairly representative of Central America, although there is comparatively little material from British Honduras. However, there are large areas, especially in Honduras and Nicaragua, into which no botanist has penetrated. The amount of material at hand is thought, nevertheless, to be sufficient to warrant the publication of a paper on the grasses. 1 Contr. U. S. Nat. Herb, 27: 1-416. pis. 1-67. figs. 1-7. 1028. 557 558 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM Central America as here understood includes Panama and the Canal Zone, Costa Rica, Nicaragua, El Salvador, Honduras, Guate- mala, and British Honduras. Central America consists of a central elevated region with low- lands along the two coasts. The mountainous part includes a few high peaks reaching an elevation of 3,500 meters or more. The chief peaks from which we have collections of plants are the vol- canoes Agua in Guatemala, Irazu and Poas in Costa Rica, and Chiriqui in Panama. The flora of the summits of these peaks is high-temperate but scarcely alpine. So far as concerns the grasses the flora of the elevated interior is in the main an extension of that of the Mexican plateau. The coastal region on the Pacific side is much drier than that on the Atlantic side. It possesses a well-marked dry season, as a result of which there are extensive "savannas," grassy treeless plains and hills, extending from Panama to Mexico. The Atlantic coastal region receives an abundance of rain and for the most part supports a tropical rain forest. The synonymy given is intended to include species described from Central America and names in general use. It is intended also to include names used for species in Hemsley (Biologia Centrali-Ameri- cana, mentioned above); in Nash (North American Flora); and in recent revisions of genera, in so far as reference is made to Central America. The names of the genera are in accord with the list of Nomina Conservanda appended to the International Rules of Nomenclature. DESCBIPTIVE LIST WITH KEYS POACEAE Flowers perfect (rarely unisexual), small, with no distinct perianth, ar- ranged in spikelets consisting of a shortened axis (rachilla) and 2 to many 2-ranked bracts, the lowest two being empty (the glumes, rarely one or both of these obsolete), the one or more succeeding ones (lemmas) bearing in their axils a single flower, and, between the flower and the rachilla, a second 2-nerved bract (the palea), the lemma, palea, and flower together eon- stitnting the floret; stamens 1 to 6, usually 3, with very delicate filaments and 2-celled anthers; pistil 1, with a 1-celled- l-ovuled ovary, 2 (rarely 1 or 3) styles, and usually plumose stigmas; fruit a caryopsis with starchy endosperm and a small embryo at the base on the side opposite the hilum. Herbs, or rarely woody plants, with usually hollow stems (culms) closed at the nodes, and 2-ranked parallel-veined leaves, these consisting of 2 parts, the sheath, enveloping the culm, its margins overlapping or sometimes grown together, and the blade, usually flat; at the junction of the two on the inside, a membranaceous hyaline or hairy appendage (the ligule). The spikelets are almost always aggregate In spikes or panicles at the ends of the main culms or branches. The perianth is usually represented by 2 (rarely 3) smull hyaline scales (the lodicules) at the base of the flower inside HITCHCOCK—THE GRASSES OF CENTRAL AMERICA 559 the lemma and palea. The grain or caryopsis (the single seed and the adherent pericarp) may be free, as in wheat, or permanently inclosed in the lemma and palea, as in the oat. Rarely the seed is free from the pericarp, as in species of 8porobolus and Elevsine. The culms of bamboos are woody, as are also those of a few genera, such as Oiyra and La&iacis, belonging to other tribes- The culms are solid in our species of the tribes Tripsaceae and Andropogoneae, in some species of Aristida, Sporobolus, and Muhlenbergia, and in a few other genera. The parts of the spikelet may be modified in various ways. The first glume* and more rarely also the second, may be wanting. The lemmas may contain no flower, or even no palea, or may be reduced or rudimentary. Most of the genera of grasses fall naturally into one of the two series or subfamilies. The remaining few are rather arbitrarily assigned to one or the other series. In the same manner, most of the genera may be assembled into distinct and well-marked tribes. Several, however, are not closely allied to the other genera in the tribe to which they are assigned, but are so placed for convenience in classification. KEY TO THE TBIBE8 Series I. POATAE Spikelets 1 to many-flowered, the reduced florets, if any, above the perfect florets (except in Pbalarideae; 1 or more sterile lemmas below in Bambuseae and in Uniola); articulation usually above the glumes. Plants woody, low or tall shrubs, often clambering, rarely tall trees. Spikelet* 1 to many-flowered, 1 to several sterile lemmas below the perfect one. BAMBUSEAE (p. 560). Plants herbaceous (somewhat woody in Arundo). Stigmas 3. Stamens 6; spikelets 1-flowered. Lemma with a long, much-contorted awn—6. STREPTOCHAETA (p. 572). Lemma awnless 63. PHARTXS (p. 618). Stigmas 2. Spikelets with 2 staminate, neuter, or rudimentary lemmas unlike and below the fertile lemma; no sterile or rudimentary florets above PHALABIDEAE (p. 563). Spikelets without sterile lemmas below the perfect floret or these rarely present and like the fertile ones. Spikelets unisexual, 1-flowered. Plants monoecious. Stamens numerous; spikelets in groups of 6 in a spike, 26. PARIAN A (p. 586). Stamens 6; spikelets single in a panicle ZIZANIEAE (p. 564). Spikelets perfect (rarely unisexual, but then not as above), usually articulate above the glumes. Spikelets articulate below the glumes, 1-flowered, very flat, the lemma and palea about equal, both keeled; glumes small or wanting. ORYZEAE (p. 568). Spikelets articulate above the glumes (rarely below, but the glumes, at least one, well developed). Spikelets 1-flowered in groups (short spikes) of 2 to 5, the groups racemose along a main axis, falling entire; lemma and palea thinner than the glumes TRAGEAE (p. 562). 560 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM Spikelets not as above. Spikelets sessile on a usually continuous rachis (short-pedicel late in Leptoohloa). Spikelets on opposite sides of the rachis; spike terminal, single, HOBDEAE (p. 562). Spikelets on one side of the rachis; spikes usually more than 1, digitate or racemose CHLORIDEAE (p. 563). Spikelets pedicellate in open or contracted, sometimes spikelike, panicles. Spikelets 1-flowered AGROSTIDEAE (p. 562). Spikelets 2 to many-flowered. Glumes as long as tlie lowest floret, usually as long as the spikelet; lemmas awtied from the hack, AVENEAE (p. 562). Glumes shorter than the lowest floret; lemmas awnless or awned from the tip or from a bifid apex. (See also Trisetum pringlei) FESTUCEAE (p. 561). Series 2. PANICATAE Spikelets with 1 perfect terminal floret (disregarding the few monoecious genera and the staminate and neuter spikelets) and a sterile or staminate floret below, usually represented by a sterile lemma only, 1 glume sometimes (rarely both glumes) wanting; articulation below the spikelets (except in Mellnideae) either in the pedicel, in the rachis, or at the base of a cluster of spikelets, the spikelets falling entire, either singly, in groups, or together with joints of the rachis; spikelets, or at least the fruits, more or less dor sally com- pressed. (Isaohne has 2 perfect florets.) Glumes membra na ceous; fertile lemma and pa lea indurate or at least as firm as the glumes; sterile lemma like the glumes in texture. Fertile lemma and palea scarcely firmer than the glumes; lower floret stami- nate or neuter, awnless, the perfect floret awned (except in Melinia). MELINIDEAE (p. 564), Fertile lemma and palea indurate or sublndurate, usually much firmer than the glumes; perfect floret usually awnless PANICEAE (p. 564). Glumes indurate; fertile lemma and palea hyaline or membranaceous, the sterile lemma like the fertile one in texture.