Here are Dendrobium arachnites and Dendrobium unicum, very similar in growth habit, size and flower color, but unicum holds its flowers erect and rolls the sepals back while arachnites does not open as much and holds its flowers down. I cannot detect any scent with Dendrobium arachnites, but unicum has what is to me a very disagreeable scent, sweet but with a kind of chemical sharpness.
Dendrobium unicum on Flickr - Photo Sharing!
Dendrobium arachnites on Flickr - Photo Sharing!