Orchidaceae (family of orchid plants) contains more than twenty thousand species and over 700 genera, and it is the biggest family of flowering plants. As a result, it’s no surprise that orchids are extremely various plants; although there are no trees and shrubs in orchid family, all other life-forms are perfectly possible within orchids. There are so many factors to classify orchids, so it is a big chance of getting confused. There are monopodial, sympodial, epiphytes, lithophytes, epidendroids, and even aqueous and terrestrials orchids, furthermore there are photosynthetic and myco-heterotrophic orchids, and all of these characteristics can come in different combinations to perfectly confuse orchid grower. The aim of this article corresponds to the problem of orchid classification that is important, because different types of orchids require different care, so you should know which type of orchid you possess to know what growing conditions you should provide to it.
The first thing to remember is the taxonomic classification of orchids. There are five currently recognized orchids subfamilies: Apostasioideae (very primitive orchids, no species in cultivation), Cypripedioideae (all Lady Slipper orchids – Cypripedium, Paphiopedilum, Phragmipedium, Mexipedilum and Selenipedium), Vanilloideae (Vanilla orchids), Epidendroideae (the majority of most popular cultivated orchids belong to this group) and Orchidoideae (the majority of European wild orchids belong to this subfamily, as well as cultivated Jewel Orchids). Vanilloideae, Epidendroideae and Orchidoideae orchids are called monandrous orchids (which means that they have only one stamen), and they are more evolutionary progressive than two other subfamilies.
The second thing is the ecological classification of orchids. From all house plants, Orchids are the most various, and they grow in different biomes and have different ecological adaptations. So called terrestrial orchids are the ones which grow in soil and have the same growing conditions and same ecological adaptations as most of other plants. Bletilla, Calante, Pleione, some Paphiopedilums and Jewell Orchids are terrestrials. They need a soil mix that mimics their natural habitats (Jewell Orchids need forest debris-mimicking soil, meanwhile Calanthe and Bletilla orchids can grow in common house plant soil mixture and even outside in subtropical areas). Epiphytic orchids grow on other plants and they have thick velamen layer on their roots; they also have some succulent features such as thick leaves covered with waxy cuticle, and pseudobulbs. The vast majority of cultivated tropical orchids are epiphytes; Phalaenopsis orchids, Cattleya, Oncidium Alliance, Dendrobium and others are mostly epiphytes. They need well-draining substrates to provide roots with so needed oxygen (velamen layer can absorb some water from humid air and provide orchid with water but also creates barrier for air, in anaerobic conditions root will die and rot, so you should water these orchids carefully and allow them to dry between waterings). Litophytes are the orchids which grow on rocks, and they also have thick velamen layer. Some Bifrenaria orchids are litophytes, as well as rupicolous Laelias, Paphiopedilums and others. They are also prone to root rotting, so you need to water them carefully and it is a good idea to pot them into lava rocks or something, mimicking rocks and stones. Another group of orchids are the aqueous orchids – there are only Spiranthe orchids in cultivation. These orchids grow in swamps and sometimes underwater, so they are a good choice to plant in aquarium or paludarium (and they are quite popular choice).
The third classification is the growth habit classification. There are monopodial orchids and sympodial orchids. Monopodial orchids have active apical meristem, and they grow upwards from that apical meristem (so called growth point) for all life, and they activate lateral meristem and produce lateral buds only for generative organs (inflorescences) or if the apical meristem is dead. Phalaenopsis, Vanda and Vanilla orchids are monopodial plants. Sympodial orchids do terminate an apical meristem when a stem grows to a final size and activate a lateral meristem after this to produce a new growth. Such stems are often succulent and can either be one nodded or have many nods, such succulent stems are water-storing organs, called pseudobulbs. Sympodial orchids with pseudobulbs are Cattleya, Oncidium, Cymbidium and many others; sympodial orchids without pseudobulbs are Lady slipper orchids and Pleurothallids (Masdevallia and Dracula orchids).
The fourth classification concerns orchid culture. Orchids can be divided to miniature orchids (such as some Bulbophyllum, Sophronitis and others), medium sized and large and giant (such as Grammatophyllum, Cymbidium and Vanilla orchids). Temperature requirements divide them to hot orchids (which require hot temperatures about 86-90 F – Vanda, Phalaenopsis orchids), warm (about 77 F – some Oncidiums, Cattleyas), intermediate (about 68 F – Cambria, Masdevallia), cool orchids (about 60 F – some Lycastas) and cold orchids (about 50 F – Dracula orchids, Ida). Another important thing in orchid growing is dormancy. Some orchids have dormancy (some Dendrobium and Coelogyne orchids need cool dormancy to bloom while Cattleyas need warm and dry dormancy), but others do not have it (most Phalaenopsis and Vanda orchids do not have dormancy). Also, orchids can be divided to “easy” orchids (which do not require very special conditions and/or can tolerate wide range of conditions – such as Phalaenopsis orchids, Dendrobium phalaenopsis hybrids, Bletilla orchids, spotted leaved Paphiopedilum) and to “difficult orchids” (which require very special growing conditions – for instance Dracula orchids do not tolerate warm temperatures and improper watering, some species Cattleyas are difficult to bloom because they have rather a sophisticated light regimen and do need a proper light day duration to bloom, Disa orchids are difficult to grow). Whereas “easy” orchids are well suitable to orchid growing beginners for their easiness, difficult orchids are often not suited for indoor cultivation at all and need specially constructed greenhouses to maintain their very special growing conditions.
So, there are many types of orchids and these beautiful plants can be divided into different groups based on their taxonomy, ecology, growth habit, and care requirements.