Gerrit Davidse

Chromosome numbers of Costa Rican grasses.

Chromosome counts are presented for 217 species of 103 genera of grasses from Costa Rica. Four of the genera and 90 of the species are reported for the first time. In addition, 26 counts differ from previous records for the same taxon. The generaGynerium, Lithachne, Luziola, andThrasya were heretofore unknown cytologically. First counts are also given for the following species:Agrostis bacillata, A. pittieri, A. sub patens, Andropogon angustatus, A. bicornis, A. virgatus, Aristida capillacea, A. jorullensis, Arundinella berteroniana, A. deppeana, Axonopus aureus, A. capillaris, A. chrysoblepharis, Bouteloua americana, B. disticha, Bromus exaltatus, Calamagrostis intermedia, C. nuda, C. pittieri, Chusquea lehmannii, C. tonduzii, Cinna poaeformis, Deschampsia pringlei, Digitaria panicea, Echinochloa polystachya, Echinolaena gracilis, Eragrostis simplicijlora, Eriochloa distachya, E. polystachya, Eriochrysis cayennensis, Festuca dolichophylla, Gymnopogon fastigiatus, Gynerium sagittatum, Hymenachne amplexicaulis, Imperata contracta, Isachne polygonoides, Ischaemum latijolium, Lithachne pauciflora, Luziola fragilis, Manisuris aurita, Panicum aquaticum, P. arundinariae, P. boliviense, P. cordovense, P. grande, P. haenkeanum, P. milleflorum, P. parviglume, P. pilosum, P. polygonatum, P. rudgei, P. stenodes, P. trichanthum, P. trichoides, P. viscidellum, Paspalum candidum, P. centrale, P. decumbens, P. fasciculatum, P. jimenezii, P. microstachyum, P. multicaule, P. nutans, P. parviflorum, P. pilosum, P. prostratum, P. pumilum, P. reclinatum, P. saccharoides, P. scabrum, P. serratum, P. squamulatum, P. standleyi, Pennisetum bambusiforme, P. distachyum, Pereilema beyrichianum, Pharus parvifolius, Sacciolepis myuros, Schizachyrium condensatum, Sorghastrum incompletum, Sporobolus ciliatus, S. purpurascens, Streptochaeta sodiroana, Thrasya gracilis, T. petrosa, T. robusta, Trisetum pringlei, T. tonduzii, Uniola pittieri, and Zeugites pittieri. In addition, the following counts are different from previous records for the same taxon:Aegopogon cenchroides, Axonopus poiophyllus, Bouteloua media, Brachiaria plantaginea, Chusquea subtessellata, Digitaria adscendens, Homolepis aturensis, Hymenachne donacifolia, Ichnanthus axillaris, I. pallens, I. tenuis, Ischaemum ciliare, Ixophorus unisetus, Oplismenus burmannii, O. hirtellus, Panicum geminatum, P. glutinosum, P. mertensii, P. parvifolium, P. sellowii, Paspalum convexum, Pennisetum nervosum, P. setosum, Polypogon elongalus, Raddia costaricensis, Schizachyrium hirtijlorum.

Steyermarkochloa unifolia, A New Genus from Venezuela and Colombia (Poaceae: Arundinoideae: Steyermarkochloeae)

Steyermarkochloa unifolia Davidse & Ellis, gen. et sp. nov. and Steyermarkochloeae Davidse & Ellis, trib. nov. are described. This species occurs in seasonally inundated white-sand soils in the Territorio Federal Amazonas, Venezuela, and Comisaria Guainia, Colombia. It has dimorphic culms and leaves. Only a single developed leaf is produced per vegetative culm. The morphology of this leaf is unique in the Poaceae in its cylindrical, solid sheath with flattened blade and absence of a ligule. Plants are polygamo-monoecious but most spikelets are unisexual. All spikelets are 3-flowered with the terminal floret always rudimentary. Male and bisexual spikelets usually have two fully developed florets, the lower usually male in bisexual spikelets, and are borne basally in the inflorescence. Female spikelets have the lower floret sterile and the second fertile. Lodicules are absent and the stamens and stigmas are terminally exserted. Anatomical studies indicate that the plant is arundinoid in all epidermal characteristics except the absence of microhairs and in most diagnostic characteristics of the blade anatomy. Steyermarkochloa is unusual in possessing vascular bundles inserted at different levels in the blade. The blades, sheaths, and roots have an extensive system of lacunae, a feature typical of aquatic plants. Although anatomical features clearly point to an arundinoid affinity, the many anomalous morphological features indicate an isolated position within the subfamily that is best recognized at the tribal level. During his intensive studies of the savannas in the Territorio Federal de Amazonas, Venezuela, Otto Huber collected an unusual grass along the Rio Temi in 1978 that could not be identified with any known Venezuelan species. A thorough search in the national herbarium ofthe Direccion de Investigaciones Biologicas (VEN) led to the discovery of an earlier unidentified collection of the same species made by E. Foldats in 1960 along the Rio Atabapo, also in Amazonas. In

FOUR NEW SPECIES OF AXONOPUS (POACEAE: PANICEAE) FROM TROPICAL AMERICA'

The following species of Axonopus sect. Axonopus are described: A. rupestris, from Goids, Brazil, A. casiquiarensis from Guainia, Colombia, and Amazonas, Venezuela, A. chimantensis from Bolivar, Venezuela, and A. jeanyae from Cocl&, Panama. Axonopus is a predominantly tropical American grass genus with a few species extending into the American subtropics and the Old World tropics. Black (1963) monographed the genus and recognized 109 species. With continued exploration it has become apparent that new species remain to be described. On the other hand, it is also probable that some of the species recognized by Black must eventually be synonymized as intermediate populations become known. Axonopus belongs to the tribe Paniceae and is distinguished by the absence of a lower glume, lower palea, and lower flower, and by its solitary, dorsally compressed spikelets borne inversely (i.e., with the back of the upper glume facing away from the rachis) in two rows on one or usually several to many racemes. This paper reports on recent fieldwork in tropical America that has brought to light four undescribed species of Axonopus sect. Axonopus. These are published now so that the names will be available for two forthcoming floras, Flora Mesoamericana and Flora of the Venezuelan Guayana.