A Beginner's Guide to Orchid Pollination by Philip Seaton
Many of the rare and beautiful species once commonly seen on show benches and in orchid nurseries are becoming more difficult to obtain. If we wish to maintain them in cultivation we need to keep an eye out for those desirable plants that remain in collections, pollinate them, grow them from seed, and share the resulting seedlings. The purpose of this little guide is to encourage more people to 'have a go', illustrating the process with examples from some of the more popular genera.
There is no substitute for looking. The first step lies in understanding the structure of the flower you wish to pollinate, being able to answer such questions as, 'Where is the pollen?' and, 'Where on the flower should I place the pollen, once I have found it?' Many orchid flowers are easy to pollinate, and I recommend beginning with some of these before progressing to more challenging species. pleiones or phalaenopsis, for example, make ideal subjects with which to practice.
Although this may not be obvious at first sight, all orchid flowers conform to the same basic plan: three sepals, three petals, and a column. The column is located in the centre of the flower. The flowers are usually 'resupinate', that is to say that, during development, the flower has rotated through 180 degrees, so that the third petal, the lip (or labellum) points downwards. Often the lip is large and showy, and helps to attract and guide the pollinator. This is not always the case, however. In masdevallias and disas, for example, the pollinator is attracted by the large brightly coloured sepals, and the lip is reduced to a tiny ‘tongue’. In the case of slipper orchids, the lip is modified to form a pouch. The column contains the male and female reproductive structures, the pollen-bearing anther(s) and the stigma, the stigma (except for slipper orchids) is separated from the anther by a flap of tissue called the rostellum. The ovary containing the ovules (eggs) is located behind the sepals and petals.
Broadly speaking, orchids fall into two groups, slipper orchids (Cypripedium, Paphiopedilum and Phragmipedium) and the rest. In slipper orchids the pollen is found as (usually brown) sticky masses located on either side of the column. We will look at them later. In the rest the pollen grains are aggregated into lumps called pollinia.
The pollinia are often hidden behind an anther cap at the end of the column. Removal of the cap may reveal two or four bright yellow pollinia (just to show that rules are meant to be broken, Cattleya (Sophronitis) cernua has indigo pollinia) nestling in two small depressions at the end of the column. Occasionally, however, the pollinia will remain in the anther cap as you remove it. In order to attach these packets of pollen to the unsuspecting pollinator, the pollinia may be attached by short stalks (caudicles) to sticky pads (viscidia), or the flower may 'glue' the pollen to its victim with a drop of adhesive produced by the rostellum. Alternatively, the pollinia can be found within a pair of pockets (bursicles).
In either case, once located, the pollen can be removed, either using a cocktail stick or fine forceps, depending on the species and the size of the flower. This should be done over a piece of white paper (so that if you happen to drop the pollen you won't lose it) in a brightly lit area.
The next question is, where should you place the pollen? The stigma of the majority of orchids is found on the underside of the column. If you are not sure about any of the above, it is a good idea to sacrifice one of the flowers (if there is more than one) and dissect and examine it with a magnifying glass. This is particularly good advice if you are looking at tiny flowers – even lepanthes can be pollinated successfully with some care.
Slipper orchids can be puzzling. The glutinous pollen masses are easily located, one on either side of the column. The stigma, however, may not be at all obvious, as it will be hidden within the shoe-shaped lip. To see the stigma either the pouch must be removed, or a window cut in the back of the pouch, thereby revealing a large, shiny disc.
Ideally flowers should be cross-pollinated with pollen from a different clone (i.e. they are genetically distinct). If the spike is made up of many flowers, you should pollinate a number. If this results in the production of several seed capsules, to get the best quality seed, the number of capsules can be reduced over a period of time. It should be borne in mind that some species are self-incompatible and, rarely, some orchids have unisexual flowers.
Of course, the flowers of the pollen parent and the seed parent may not be open at the same time. Pollen may, however, retain its viability for several months if is dried to a suitable moisture content and kept in an air-tight container (small Kilner jars are ideal) in a refrigerator at 5 degrees Celsius.
How do you know if you have been successful? Cymbidium flowers 'blush'. In some species the petals and sepals collapse and gradually wither and die, in others (such as Phalaenopsis violacea) the petals and sepals remain and turn green.
Angraecum, Odontoglossum and Phalaenopsis
An unlikely grouping at first sight perhaps, but in all three genera two pollinia are attached to a viscidium. If a cocktail stick is gently inserted into the centre of the flower just below and touching the column, you will usually find that the viscidium with two pollinia attached will become firmly glued firmly to the stick.
Cattleya, Masdevallia and Pleione
Often large and showy, with brightly coloured sepals of vibrant reds, yellows and oranges, the much-reduced petals and tiny mobile lip of masdevallias are hidden in the tubular throat of the flower, and can be difficult to find without the aid of a hand lens. Yet the basic structure is the same as that of cattleyas and pleiones. The pollinia are hidden behind the anther cap, and become coated with a glue from the rostellum as they are removed.
Cypripedium and Paphiopedilum
To see the stigma either the pouch must be removed, or a window cut in the back of the pouch, thereby revealing a large a shiny, and it has to be said, unpromising stigma on which the pollen should be generously smeared. As a general rule, you should smear as much pollen as possible onto the stigma.
Disa and Dactylorhiza
Two pollinia are hidden in pockets (bursicles). Each club-shaped pollinium (considerably elongated in disas) has a small stalk attached and a sticky pad, so that if a sharp pencil or a cocktail stick is inserted into the flower, one or both pollinia will adhere to it. Under the microscope the pollen grains can be seen to be bound together in units of four (tetrads). These in turn are bound together by elastic material into massulae, so that when a pollinium touches the stigma, some pollen grains will adhere to the fluid. The stigma of dactylorhizas is found in the ‘conventional’ location beneath the column, but that of Disa uniflora is a simple shiny pad.
Pollination of Disa uniflora
All images and drawings © Philip Seaton