The existence of natural hybrids was formerly thought by some naturalists to be highly improbable, if not
actually impossible. But now, when absolute facsimiles of supposed natural hybrids have been raised by
hand in gardens, from the same two species among which they grow, they can no longer be regarded as
pious speculations, but are indeed accomplished facts.

The number of proved hybrids in orchids alone is now very considerable, with the result that many intermediate and doubtful forms, hitherto classed as distinct species, are now placed in their proper position as natural hybrids. Mr. R. A. Rolfe, of Kew, has done yeoman service in reducing the chaos of natural hybrid orchids to something like order.

And so it has come to pass that artificial hybridisation, which it was supposed would lead systematic botany into the direst confusion, by the irony of fate, seems destined to be the only trustworthy means of saving systematic botany from its own confusion; and the systematist, however orthodox he may be, can no longer afford to ignore artificial hybrids.

- C. C. Hurst. Curiosities of Orchid Breeding. Nature vol 59, 1898 [1]

"A species is a species; it can reproduce itself but it does not hybridise with other species.
During evolution species become more and more isolated from each other, and so different genotypes prevent hybridization"[2].

Orchid hybrids

But orchids are evolutionarily a young family. Many orchid species, even genera, are so similar
in genotype that natural or artificial crossings are possible. The resulting seeds can grow to be hybrids. Most orchids you buy from florists are hybrids, created and reproduced by people.

In nature hybrids are much less common, and in many cases sterile and not able to reproduce. But sometimes fertile hybrids do occur. When such fertile hybrids find a suitable habitat, over
time their populations grow. So, some say, a new species is born.

This does happen with wild orchids. Examples in New Zealand are

Thelymitra pulchella (= T. cyanea x T. longifolia s.l.);
T hatchii (= T. formosa x T. longifolia s.l.),
T. tholiformis (= T. aemula x T. pauciflora s.l.) and
T. decora (=T. nervosa) (= T. aff. ixioides x T. longifolia s.l.) [3].

Natural hybrids between Nematoceras species may also occur in the wild - putative N. macrantha x N. "Trotters", N. hypogaea x N. longipetala and N. iridescens x N. triloba hybrids have for instance been illustrated in recent issues of this journal.

Within-species variation may of course be as great as between-species variation, so we should not claim a hybrid from every morphological peculiarity. We are a long way from proving intermediate forms of Pterostylis are actually hybrids.

Some natural hybrids are not very variable, so they are easy to identify - for example T. hatchii (though even that has different colour forms). Others may be hard to distinguish from their parents, especially when the parents resemble each other, or when one of the parents is itself variable. One parent may be easy to identify, but the other may be open to question (exactly the case with the different forms of T. longifolia, one or more of which might be a parent).

Moreover in most cases the structural characters of the hybrid are not exactly intermediate between those of the parents. Depending on the distribution of the chromosomes, the hybrid may resemble one parent more than the other. Thus there can be wide variation in the form of hybrids from the same parents.

For a good example look at the different plants once thought to be distinct from Thelymitra pulchella (= T. cyanea x T. longifolia s.l.), but now regarded as synonyms - T. caesia, T. pachyphylla, T. concinna, T. fimbriata. (The hybrids must of course result from cross-pollination, which assumes insect pollination, which in turn assumes one of the T. aff. longifolia taxa rather than T. longifolia s.s. - though even that self-pollinator may be visited by an insect on a sunny day).

It is still possible of course that those different forms of T. pulchella result from T. cyanea crossing with different, undescribed, forms of T. aff. longifolia. Both Catherine Beard and I have commented on the different forms of T. cyanea in this journal. A dozen forms of the hybrid between the European Ophrys holoserica and Ophrys insectifera can be viewed via the website www.orchis.de/orchis/docs/e004.htm.

Between-species (interspecific) hybrids are distinguished from between-genera (intergeneric) hybrids. The former means hybrids between species of the same genus (Nematoceras for example), and they are likely to be relatively more frequent than hybrids between species of different genera.

In Europe Ophrys, Orchis and Dactylorhiza have a greater tendency to hybridization than others.
In New Zealand, Thelymitra has the stable hybrids mentioned above, but there are others - undescribed plants from the Far North, and the sterile Thelymitra "Comet" are examples.

Hybrids between species of different genera can be relatively common; in Europe combinations of Aceras anthropophorum and species of the genus Orchis are relatively frequent, but absolutely very rare. In New Zealand I know of no naturally occurring intergeneric hybrids, though the handmade hybrid Calomitra (Calochilus x Thelymitra) has been created in New Zealand (Doug McCrae) and Australia (Heinrich Herberle), and that between Sarcochilus and Drymoanthus (Sarcomoanthus) in New Zealand (Malcolm Campbell) [4].

Is it a hybrid?

How do we prove an orchid is a hybrid? Lets look at the examples in J93 pages 26 and 39.

A structure intermediate between putative parents makes a hybrid more likely (but the opposite
is not true - the characters of a hybrid may not resemble those of its parents). A site close to
the putative parents makes a hybrid more likely (but the opposite is not true - as orchid seeds
are light, hybrid seeds may germinate and grow at a distance from the parent species).

An example is the naturally occurring hybrid Thelymitra carnea (= T. flexuosa x T. pauciflora) which clearly originated in Australia, but is present in New Zealand in the absence of its parents. On the contrary it is not legitimate to determine a hybrid solely by the presence of two possible parents growing beside it. Proof depends on the manmade reconstruction of the hybrid by artificial cross-pollination between the parents, as Doug McCrae and Brian Molloy demonstrated for the natural hybrid Thelymitra xdentata [5].

Now the examination of sequence data from the nuclear ribosomal DNA spacer region (ITS1, ITS2, and 5.85 gene), which Jones, Clements and Molloy have used to separate genera and species, appears to be useful for detecting hybrids.

Ploidy

Almost every cell in every plant or animal contains two of each kind of chromosome. I have 23 pairs of chromosomes (i.e. 46) in each of my body cells. So do you. Our gametes (egg and sperm cells) each have a single set of 23, so when they combine to form a zygote (which will become an embryo), the two different parental lots of 23 combine to form our child's own 46 [6]

Thus the normal state of a human gamete is 23, the "haploid" state (1N), and the normal count
of a human body cell is 46, the double, or "diploid" state (2N). 1N + 1N = 2N. Easy as ABC.

It's the same for hybrids; even if they have different chromosome numbers, each contributes
half its number to the zygote (offspring).

For example:
T. longifolia (2N=26; N=13) x T. pulchella (2N=66; N=33) = T. xdentata (2N=13 + 33=46).

Polyploidy simply means a multiple of diploidy or 2N. Thus 3N, 4N, 5N, 6N are polyploids.

With chemicals such as colchicine we can double the chromosome number of plant cells to
form tetraploid cells (tetra = four, or 4N), or octaploid cells (octo = eight, or 8N). In nature, autotetraploidy sometimes happens, presumably as a result of chemical or solar mutation; Drymoanthus adversus (4N=76) is an autotetraploid of D. flavus (2N=38).

The Eurosiberian Dactylorrhiza maculata appears to be a stable autotetraploid of D. fuchsii.
I have wondered if the large, double-flowered Singularybas oblongus found in small colonies around New Zealand is simply a habitat variation, or is an autotetraploid.

Chromosomal instability may follow hybridisation, so the first generation offspring later
experience a spontaneous doubling of chromosomes. This is similar to autotetraploidy but
because the parents may have different chromosome numbers it is known as amphidiploidy;
it appears to have happened to several Thelymitra hybrids in New Zealand.

Thus...

T. aemula (2N=40) x T. aff. pauciflora (2N=26) = T. tholiformis (2N=66) amphidiploid;

T. aff. ixioides (2N=28) x T. longifolia s.l.(2N=26) =T. decora (T. nervosa) (2N=54) amphidiploid;

T. cyanea (2N=40) x T. longifolia s.l. (2N=26) = Thelymitra pulchella (2N=66) amphidiploid;

T. formosa (2N=40) x T. longifolia s.l.  (2N=26) = T hatchii (2N=66) amphidiploid.

An amphidiploid is defined as a hybrid of two different species which has two sets of chromosomes from each of the parent species. It is thus an alloautotetraploid; a tetraploid formed from the union of two different chromosome sets and their subsequent spontaneous doubling.

No simple diploids of these hybrids are known, so the assumption is that the first generation
(diploid) hybrid was sterile, but regained its fertility when amphidiploidy took place; so that
had to be early.

Naming hybrids

What are we to call orchid hybrids? Usually they are not named, although it is possible to :describe them formally. Appendix 1 of the Code guides us [7].

A hybrid is indicated by the use of the multiplication sign x or by the addition of the prefix :"notho-" to the term denoting the rank of the taxon. Thus Thelymitra xdentata is a nothospecies.

A nothotaxon cannot be designated unless at least one parent is known or can be postulated.

A hybrid between named taxa may be indicated by placing the multiplication sign between the
names of the taxa; the whole expression is then called a hybrid formula. It is preferable to place
the names in a formula in alphabetical order. Thus Thelymitra xdentata = T. longifolia s.l. x
T. pulchella.

A nothotaxon is circumscribed so that it includes all individuals derived from the crossing of
the parent taxa (i.e. not only the first but subsequent generations and back-crosses and combinations of these). There can thus be only one correct name corresponding to a particular hybrid formula; this is the earliest legitimate name in the appropriate rank, and other names to which the same hybrid formula applies are synonyms of it. This applies to the various names given to Thelymitra pulchella (see above).

The nothogeneric name of a bigeneric hybrid is a condensed formula in which the names
adopted for the parental genera are combined into a single word, using the first part or the
whole of one, the last part or the whole of the other (but not the whole of both) and, optionally,
a connecting vowel. Thus Sarcomoanthus for Malcolm Campbell's intergeneric hybrid between Sarcochilus and Drymoanthus.

When contemplating the publication of new names for hybrids between named taxa, authors should carefully consider whether they are really needed, bearing in mind that formulae, though more cumbersome, are more informative. Thus it is actually more useful to identify the putative hybrid Bruce Irwin drew on page 26 of J93 as Nematoceras iridescens x N. triloba than it would be to give it a new name.

Names published at the rank of nothomorph are treated as having been published as names
of varieties. Thus Thelymitra caesia might be called T. pulchella var. caesia, T. uniflora might
be called T. cyanea var. uniflora.