Two new records and one rediscovery for Orchidaceae of Mexico

two orchid species, both previously known from central america, are reported for the mexican flora: oncidium poikilostalix and telipogon helleri. the former species was previsouly known under the name sigmatostalix poikilostalix, and the latter as stellilabium helleri. the rediscovery of another mexican orchid, plectrophora alata, is also reported, having been registered in the country 75 years ago, but not collected since then, and presumed extinct. these three species were recently discovered in the rainforest of the tacaná volcano region, in chiapas. each species is described and illustrated based on the mexican specimens and their similarities with related taxa are discussed.