Journal Number 103
May 2007


EDITORIAL

Monsters, Freaks, Retrogrades and Primitives
By Ian St George


Calochilus imberbisThe Australasian orchid tribe Thelymitreae is composed of Calochilus, Epiblema, and Thelymitra. Evidence from floral structure suggests that Epiblema and Thelymitra are sister genera and that Calochilus is derived from a Thelymitra ancestor [1]. Indeed, Calochilus robertsonii occasionally "throws back" to a peloric flower similar to that of Thelymitra, a form originally described as Calochilus imberbis ( Fig Right ).

Mistakes in plant structure include fasciations, an enlargement and flattening of a plant structure, especially the inflorescence; peltation, the formation of leaf-like structures in place of perianth segments; and peloria [Gr: pelos: a monster], an abnormal regularity in normally irregular flowers [2].

Many orchid species have peloric forms, usually reversions to a primitive, more lily-like flower - the labellum or dorsal sepal showing features more like those of the simpler petals and sepals for example.

Dan Hatch wrote of Petalochilus in 1948, "Petalochilus is considered to be a local development, probably derived from an early form of Caladenia carnea. The undifferentiated labellum is not of itself important. The specialised labellum of the average orchid is a petal adapted to the requirements of pollination. When that function is taken over by another organ (as happens in Petalochilus) the labellum falls into disuse and thence into decline, reverting in this instance to its original petaloid condition.

Petalochilus then appears to be a retrograde to Caladenia rather than the representative of a primitive form. Nicholls (Via. Natr., 61, 1945, 207; figs. k, l, m ( see figures lower down this page)) has unconsciously demonstrated that Caladenia could give rise to such a form as Petalochilus.

He describes a couple of teratological specimens of Caladenia menziesii R. Br. in which the labellum has
become petaloid, although still retaining vestigal calli, and the column-wings have fused to form a cavity
embracing the lower two-thirds of the column. The staminoid appendage. which distinguishes Petalochilus
is, however, absent in these Caladenia specimens. Petalochilus saccatus is probably derived from an early
form of P. calyciformis by a fusion of the column-wings with the staminoid appendage [3]." The column
itself may revert to a more-or-less lily-like set of stamens and carpels.
 

Petalochilus calyciformis, a peloric form,
probably of Caladenia chlorostyla

  Petalochilus calyciformis


Peloric Forms


Peloria is a genetic mutation, but expression of peloria may be influenced by environmental changes or by
being stressed. Peloria is not always stable, and the plant may flower normally on the next inflorescence.
Sometimes the simple petals adopt the more complex structures of the labellum.
 

"Two specimens of a singular form of Caladenia menziesii, R.Br., were found at Portland by Mrs. F. Mellblom in November, 1943.

The flower is much larger than in the typical form, the labellum petaloid with undulate, incurved margins and papillate glands. Figs. K, L, M."

(WH Nicholls. A new Variety of Sun-Orchid. Victorian Naturalist 1945; p207).

  Caladenia menziesii


Some peloric orchids are being mericloned, bred, and marketed. In Dendrobium "Classic Gem" (below)
and its progeny the lip has reverted back to looking like the petals. Rhyncolaelia digbyana var. fimbripetala
( below ) has slightly fimbriated petal margins, which has given rise to a host of modern splash-petal hybrids,
many having received AOS quality awards. There are many awarded splash-petal Cattleyas. Phragmipedilum
lindenii has a long petal in place of a pouch.

Dendrobium "Classic Gem"   peloric cultivars
Dendrobium "Classic Gem"
with its petaloid labellum
  A couple of peloric cultivars with petals like their labellum
     
Phragmipedilum lindenii   Rhyncolaelia digbyana Rhyncolaelia digbyana var. fimbripetala
Phragmipedilum lindenii
with its petaloid labellum
  Rhyncolaelia digbyana
with normal petals
Rhyncolaelia digbyana var. fimbripetala with partly labelloid petals
       

Some orchid growers find beauty in peloric flowers, but in American Orchid Society judging, some feel
that "peloric orchids that display a complete inflorescence of deformed flowers should automatically be
disqualified from further consideration" [2].

The ABC model of flower development was proposed when scientists found that certain genes in flowers
produced effects related to these genes. By knocking out one of the genes, they discovered which coded
for what. For example, when they removed the C class of genes, the plant lost the ability to produce sexual
parts (stamens and carpel(s)).

  •  The A gene produces sepals.
  •  The B gene produces nothing on its own.
  •  The C gene produces carpels.
  •  A combination of A and B produces petals.
  •  A combination of B and C produces stamens.

Mutants lacking the A gene will only produce stamens and carpel(s). This mutation is known as APETALA.
Mutants lacking the B gene will only produce sepals and carpels. This mutation is known as PISTILLATA.
Mutants lacking the C gene will produce sepals and petals, over and over again.
This mutation is known as AGAMOUS.
These mutations can occur at random in the wild or they can be artificially induced [4].

Man has cultivated the mistakes found in nature: the mistake where disk florets have become ray florets has
led to the doubling of marigolds, zinnias and chrysanthemums. Some roses have stamens modified into
petal-like structures. Curiosities such as the weeping pussy willow, or the contorted Harry Lauder's walking
stick can now be easily obtained.

What then of Kevin Matthews's twin-leaved Caladenia's and Thelymitra's (pp 24-25)? I can find few references
to reversion to primitive leaf (as opposed to flower) structures, but I guess that is what has happened here.

Primitive orchids such as Neuwiedia and Apostasia have multiple leaves, and Protorchis monorchis, one of
very few fossil orchids ever found, also had several leaves. So, of course, do lilies. It might be surmised then,
that more than one leaf on a single-leaved plant should represent a mutation, a natural mistake, the structure
reverting to the more primitive form.

Should we call these mutants species? Calochilus imberbis and many others have been named.

A species, Eric Scanlen suggests in this issue, is a taxon following its own evolutionary path. By that definition,
these would be species - even if the evolutionary path leads to extinction. Eric qualifies that: seed propagation
is axiomatic to a viable species. So does "following its own evolutionary path" actually contribute any meaning helpful to the debate?

I don't think these are species. These are forms or varieties of species. I like the names Rhyncholaelia digbyana var. fimbripetala, "Calochilus robertsonii forma imberbis", and (if it hadn't already been named Petalochilus calyciformis) "Caladenia chlorostyla forma calyciformis". Lets keep it simple.


Primitive orchids
 Primitive orchids - Above left: Neuwiedia - Above right: Apostasia



References

1. Burns-Balogh P, Bernhardt P. Floral evolution and phylogeny in the tribe Thelymitreae (Orchidaceae: Neouioideae).
    Plant Systematic's and Evolution 1988; 159 (1-2 / March): 19-47.
2. http://angrek.com/AAOS/Past/9802/Txt/Peloria.html accessed 17 January 2007.
3. Hatch ED. Petalochilus Rog. and the New Zealand Forms of Caladenia R. Br. 1948; 77: 398-402.
4. http://en.wikipedia.org/wiki/The_ABC_Model_of_Flower_Development accessed 17 January 2007.

 

 

 

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