I'm not certain if you really mean "species" or not. I myself have a hard time knowing what level of taxonomy I mean to reference when talking types of orchids - levels go like this - Family - Subfamily - Phylad - Tribe - Subtribe - Genus - Species - Variety. For example, when talking species you would have all the following in the same group - Laelia purpurata, Laelia pumila, Laelia anceps, Laelia harpophylla, Laelia rubescens, & Laelia tenebrosa. At this level the plants are closely related - the flowers themselves I believe are the most important here. Within each species there will be experts that can probably narrow things down pretty close by size & shape of the plant itself as well. Once you start talking hybrids some plants are absolutely impossible to accurately type as there are literally several hundred thousand out there and many are similar in many or all characteristics to others. Generally the "type" of orchid is initially classified on a broader level - perhaps the term "alliance" is used, to designate a group of genera that have common characteristics - like phalaenopsis, cattleya, paphiopedelum, cymbidiums, etc. These can be often grouped by folliage alone and then narrowed down further by the flower depending upon which one it might happen to be. Hope this helps some - kind of a broad topic. If you are really interested in the taxonomy of orchids you might take a quick look at the following link to give you an idea of the breadth of what you are talking about - it is the largest family of plants on mother earth!
http://en.wikipedia.org/wiki/Taxonom..._Orchid_family