Cleistes

Abstract: The survey of the Orchidaceae from the Distrito Federal (DF), the administrative region of the Brazilian capital located at the center of the country, is presented. Currently, 72 genera and 254 taxa (246 species and eight subspecific taxa) are recognized, 17 (6.7%) of which are known only locally. The most representative genera are Habenaria (74 species and three subspecific taxa), Cyrtopodium (17 species), Cleistes (13 species) and subtribe Spiranthinae (11 genera, 34 species and two subspecific taxa). Genera like Epidendrum (eight species), Pleurothallis (seven species), Oncidium (six species) and Maxillaria (three species) are abundant in the Atlantic rain forest in southeastern Brazil, but poorly represented in the region. About 73% of the Orchidaceae from the DF are terrestrials, in contrast with the Atlantic forest and Amazon region, were the epiphytes predominate. The Distrito Federal is the better-sampled region and has the higher number of Orchidaceae in the cerrado region, comprising about 51% of the orchids known from this biome. The aim of this survey is to subsidize the monograph of the family for the forthcoming "Flora of the Distrito Federal".

Abstract: A population of Cleistes divaricata (L.) Ames var. bifaria Fernald, at its northwesternmost range limit and rare in West Virginia, more than quadrupled in numbers between 1980 and 1986 in an acidic, nutrient-deficient West Virginia meadow that is mowed annually. The aerial, upright ramicauls (stems) may be vegetative with one to three leaves; when flowering, they typically bear one flower, one cauline leaf, and a floral bract. Long-lived flowers exploit naive bees, operating as rewardless bee-foodflower mimics. A hinged anther drops clumps of pollen tetrads onto the dorsal thorax of Bombus and Megachile workers. Pollination is effected when bees deposit pollen in flowers visited subsequently. Field capsules with 120 to 11,000+ seeds result from xenogamous and geitonogamous pollinations. Scarcity of pollinators and occasional severe herbivory of flowers and capsules lower reproductive output. Reproduction is enhanced by production of healthy pollen, low pollen to seed ratio, a highly efficient pollination mechanism, and high embryo viability.

Abstract: The Orchidaceae have dust-like seeds that use wind currents for long-distance dispersal. Lacking endosperm, orchid embryos consume free-living, mycorrhizal fungi as a carbon source (mycotrophy) after settling on a substrate. Few studies have investigated orchid seed morphology as it relates to ecology, but conceivably variations in seed size and testa characteristics could be linked to water loss rates aimed at maximizing germination in a particular habitat. Seeds of 2 epiphytic, 1 aquatic, and 7 terrestrial orchids native to North America were compared with respect to water balance profiles: Cleistes bifaria, Encyclia tampensis, Epidendrum nocturnum, Habenaria repens, Isotria medeoloides, Liparis elata, L. hawaiensis, Platanthera holochila, P. integrilabia, and P. leucophaea. Water content, water loss rate, activation energy, and equilibrium humidity were assessed for each species. Seeds of epiphytic orchids were smaller, lighter, more porous, and had higher water loss rates compared to terrestrials. No active mechanism for water absorption exists in seeds of either group. Water loss appears to be a species-specific phenomenon that may be linked to the ecological niches these species occupy.

Abstract: Cleistes macrantha (Barb. Rodr.) Schltr. is widely distributed in Atlantic rain forests in south and southeastern Brazil, occurring in anthropogenic disturbed areas and in "restinga" vegetation. Aspects of the floral biology of C. macrantha were investigated in the Intervales nature reserve, in the interior of Sao Paulo state. This species offers nectar as reward and is pollinated principally by bumblebees. The nectar is secreted before the anthesis of the flowers, with no posterior secretion. Hermit hummingbirds can also act as pollinators. A previous visit of a bumblebee, however, is necessary for pollen deposition on their bills. Bumblebees are responsible for most cross-pollinations. The hummingbirds perform mainly self-pollination. Preliminary treatments reveal that C. macrantha is self-compatible, but a pollinator is necessary for successful pollination. In spite of the self-compatibility observed, ecological factors favor cross-pollination in this species. This study makes too, a comparison of the floral biology of C. macrantha with what is known about the genera of the North American-Asiatic clade in Pogoniinae.