Richard W. Pohl

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.

Stem aerenchyma as a character separating Hymenachne and Sacciolepis (Gramineae, Panicoideae).

Hymenachne andSacciolepis, two closely related tropical genera, have been distinguished by the saccate second glume in the latter, a trait lacking in the former. It is difficult to assign certain species to genus on this basis alone. A survey of both genera showed that aerenchyma fills the stem pith region ofHymenachne species but is absent or nearly so fromSacciolepis species. The leaf epidermis ofHymenachne bears prickle cells, which have not been reported fromSacciolepis. Additional anatomical details are given forH. amplexicaulis.

Cytogeography of the rhizomatous American species of Muhlenbergia

The grass genus Muhlenbergia is estimated to contain 80 (Bews 1929) to 120 (Hitchcock 1936) species, confined to the western hemisphere with the exception of several species of Japan and the Himalaya. The genus belongs to the subfamily Chloridoideae, as evidenced by its plump bicellular hairs, rhombic stomata, siliceous cells, embryo characteristics (Reeder 1957), and chromosome number and size. Two rather distinct groups of species comprise the genus. The group which we have studied consists of broad-leaved, mesic, rhizomatous plants, primarily distributed in the deciduous forests of eastern North America. A few species extend far beyond the limits of this vegetational formation into the plains and western mountain states, and several closely related species are found in Japan and the Himalaya. The distribution pattern of the group and the association of many of the species with the deciduous forests suggest that its ancestors were part of the Arcto-Tertiary Geoflora. The plants of this group are readily recognized, even in vegetative condition, by their numerous rather lax, short culm leaves and by their peculiar scaly rhizomes. These species are radically different in vegetative structure and ecological relationships from the xeromorphic cespitose species of our western plains, and probably have had a different origin. The apparent basic chromosome number of the genus Muhlenbergia is x = 10. Diploids, tetraploids, hexaploids, and one octoploid have been found. Among the broad-leaf species, the two diploids are rare though wide-ranging, occurring in scattered relict stands in highly specialized habitats. Muhlenbergia asperifolia, which is also diploid, is a xeromorphic species of alkaline or saline habitats in the West. It bears no obvious relationship in habit, leaf structure, rhizomes, or habitat preferences to the other diploids. The tetraploids are common, abundant, and ecologically diverse. The single octoploid, M. californica, is a rare endemic in several mountain ranges in the Los Angeles area. All cytological observations were made on acetocarmine or propriocarmine squashes of microsporocytes. The slides were made permanent by the rapid liquid carbon dioxide method of Bowen (1955). Inflorescences were obtained from greenhouse-grown plants produced from living rhizomes collected in the field. The rhizomes grow readily and the plants ordinarily will bloom several times a year if they are cut back and fertilized after flowering. Supplemental light was provided during the winter. Meiosis follows a strong diurnal pattern, with diakinesis occurring most frequently around 7:50 AM in mid-June and 10 AM in late December. Since diakinesis lasts less than ten minutes, fixation at the correct time is important. Voucher specimens for the chromosome counts are deposited in the Iowa State University Herbarium. Gametic chromosome numbers for the rhizomatous American species of Muhlenbergia discovered in the course of this study or reported in the literature are summarized as follows, and some gametic chromosome complements are illustrated in Fig. 1-13.

Three New Species of Rhipidocladum from Mesoamerica

Rhipidocladum clarkiae Pohl and R. pacuarense Pohl are described from Costa Rican flowering material and R. panamense Pohl is described from flowering specimens from Panama. The genus Rhipidocladum was erected by McClure (1973) to include species of bamboos previously assigned to Arthrostylidium, Arundinaria, and Ludolphia. The species of Rhipidocladum are slender and graceful. At each midculm node, they bear an adnate triangular flat meristematic branch that produces numerous foliage-bearing lateral branchlets in a fan-shaped (apsidate) array. The genus is differentiated vegetatively from Merostachys, which has a similar branchlet array, by the nature of the main culm leaves. In Rhipidocladum, the base of the erect culm blade is as wide as the apex of the sheath and adnate to it. In Merostachys, the reflexed blade of the culm leaf is pseudopetiolate and much narrower than the sheath apex. The species of Rhipidocladum are slender bamboos, ranging from 2 to 10 m or more in length and 1 to 5 cm diam. They inhabit mesic sites in moist forests and are found on canyon walls and river banks at low and middle altitudes. The genus ranges from southern Mexico to northern South America, with one species reported from Brazil. McClure indicated that his genus included 11 species and offered a key to distinguish some of these. One species, R. verticillatum, has since been transferred to a new genus, Actinocladum, by Soderstrom (1981). With the addition of these three new species, the current number is 13. Mesoamerican species of Rhipidocladum are not well known because of their erratic blooming cycles. Recent gregarious flowering of two Costa Rican species and one from Panama has allowed differentiation of species previously known only in the vegetative condition. Two of these species, R. clarkiae and R. panamense, are distinct from the remaining species of the genus because of their extremely large number of fiiform branches. The third, R. pacuarense, is most closely related to R. bartlettii of the Peten of Guatemala and Chiapas, and their differences are stated in Table 1. In the absence of adequate type material of many of the species, detailed comparisons with the remaining species cannot be made. The key given by McClure (1973) offers the best separa-

New species of Festuca, Sporobolus, and Eriochloa (Poaceae) from Mesoamerica and South America

As a result of work on the Poaceae for Flora Mesoamericana, the following four new species are described, illustrated, and compared with their closest putative relatives: Festuca talamancensis from the Cordillera de Talamanca in Costa Rica, F. herrerae from the Cordillera de Talamanca in Costa Rica and Panama, Sporobolus distichivaginatus from the Peten, Guatemala, and Eriochloa stevensii from Nicaragua, Venezuela, and Ecuador. In addition to the new species of grasses recently described as the result of a review of the Poaceae for Flora Mesoamericana (Davidse & Pohl, 1992), the following four species were found to be new and are here described, discussed, and illustrated for the first time. As in the earlier paper, the new species are published under the name of the person primarily responsible for the account of the taxon.