Eria mêdogensis

a Probably Peloric Form of Eria Coronaria, with a Discussion on Peloria in Orchidaceae
Chen Sing-Chi, Tsi Zhan-Hue
(Institute of Botany, Academia Sinica, Beijing)

Eria mêdogensis S. C. Chen et Tsi was recently found in southeastern Tibet, se-
veral specimens of which have been collected by various botanists since 1980. This is a “normal”
entity with its habit very similar to that of Eria coronaria, from which it differs by having a
regular perianth and longer bracts. We think it probable that this new entity is a peloric form
of Eria coronaria.
Peloria (or pelory) is a type of floral abnormality, which is found in many zygomorphic-
flowered taxa. It was first detected by Linnaeus (1744) in Linaria vulgaris, and then by others
in Labiatae, Orchidaceae, etc. However, it is still an open question how to explain it theoretical-
ly and how to treat it taxonomically.
In Orchidaceae, so far as our knowledge is concerned, peloria has been encountered in no
less than 21 genera. In most cases, peloric flowers are found sporadically on an occassional plant,
as seen in Cypripedium reginae and Eria oblitterata. Sometimes, however, peloric form may occur
coexisting with normal-flowered form in one and the same species, as seen in Dendrobium tetro-
don and Epipogium roseum. They are both abnormally peloric forms. It would not result in
naming or renaming a plant taxonomically, whether the appearance of abnormally regular flo-
wers on a normal-flowered inflorescence, or of abnormal-flowered individuals in normal-flower-
ed species. In Phragmipedium lindenii, however, the case is different. It is quite “normal” and
even of wider distribution than its nonpeloric allies P. wallisii and P. caudatum, from which
it has once been considered to be derived. This is a normally peloric form. Whether it is a
reversal or not, the appearance of a “normally” peloric taxon may be taken for a leap in the
process of evolution. Taxonomically, we had better treat it as a separate species, especially when
its origin is uncertain. For example, the entity just mentioned had been treated as a peloric va-
riety of Phragmipedium caudatum (var. lindenii) until 1975, when Dressler & Williams recogniz-
ed it as an independent species based on the fact that its nonpeloric flowers occassionally found
in a peloric population in Jungurahua of Ecuador are dissimilar in lip to those in P. cauda-
tum. Garay (1979) considered it to be a peloric form of P. wallisii but maintained it at the
specific level. This is indeed a good example of taxonomic treatment of normally peloric form.
On the other hand, however, most of the regular-flowered entities in Orchidaceae are not
peloric but rather primitive forms, such as Neuwiedia, Apostasia and Thelymitra, of which no
less than 50 species have been reported since the eighteen century. They have never been regarded
as peloric forms. Unfortunately, this has been neglected by some botanists. For instance, a hypo-
thetically primitive orchid flower designed by Pijl & Dodson (1966) has a distinctly specialized
lip with a short spur. In fact, in addition to the aforementioned genera we have some more ex-
amples of normally regular-flowered orchids. Among them Archineottia is the most interesting.
This is a genus of four species, two of which are regular-flowered. Of special interest is that in
this genus and its ally, Neottia, one can find all steps of column evolution from a simple form
with stamen and style not fully united to a most complicated form in which they have well fused.
Archineottia has a very primitive column, on which neither rostellum nor clinandrium is found
but a terminal and undifferentiated stigma (Fig.2: 2, 4, 6, 8). In addition, there exists on the
back of the column a thick ridge with its upper end joining the filament with which it is of
same texture. It is obviously the lower part of the filament which has been adnate to the style
(column). In Neottia, however, the column is much more advanced and very typical among the
family. It has a very large rostellum and most complicated stigma structure (Fig. 10, 12, 14, 16,
18). One of the most interesting examples is Neottia acuminata, in which the stigma even
becomes lamellate and almost backwards clasps the erect rostellum, but the perianth is more or
less regular with its lip entire and somewhat similar to, but shorter and wider than, the petals.
In these two genera there are altogether three species, namely Archineottia gaudissartii, A mic-
roglottis and Neottia acuminata, possessing regular or nearly regular perianth (Fig. 2: 1, 3, 17).
They are obviously not peloric forms. We can not imagine, indeed, that a complicated form
like Neottia acuminata or its allies would degenerate step by step into a simple form, and finally
into a peloric form. Archineottia belongs to the subtribe Listerinae, which is closely related to
Limodorinae, a rather primitivs subtribe with some genera possessing single pollen grain, relati-
vely few and long chromosomes and monocotyledonous habit. Apparently, there is nothing sur-
prising in the occurrence of some normally regular-flowered taxa, such as Archineottia, Diplan-
drorchis, Tangtsinia and Sinorchis, in these two primitive subtribes.
Another instance is Aceratorchis, a genus formerly included in Orchis, from which it is dis-
tinguished by the entire lip which is more or less similar to the petals. Strictly speaking, howe-
ver, its flowers are not truly regular. Two species have been described in this genus, but they
were recently considered as conspecific. Aceratorchis tschiliensis is widely distributed from
Hebei through Qinghai and Sichuan to northwestern Yunnan. It is cross-pollinated and produces
seeds efficiently. All these indicate its normally primitive taxon, instead of peloria. It may be
noted here that Asia is rich in members of Orchidioideae, as well as its primitive representatives.
The occurrence of a normally regular-flowered form in Asia, whether representing primitive
form of Orchis or Orchidioideae, is imaginable.
In Orchidaceae, as mentioned above, regular flowers are not only found in some primitive
taxa and peloric forms, but also in a few advanced groups. For example, a close investigation
by the senior author (Chen 1979) on Satyrium ciliatum revealed that this species has hermap-
hrodite, staminate and pistallate forms, for which no less than nine names have been published.
The flowers of its pistallate form are almost regular, in which nothing is found but three
similar petals and an elongate style with three stigmatic lobes at its top (Fig. 2: 19).
It is interesting to note that floral reversions in Orchidaceae are not always in connection
with peloria. For example, Epidendrum triandrum of North America represents another kind
of reversion. It is a reversal to abnormal polymery of stamens and not to abnormal regularity
of perianth. Like Phragmipedium lindenii, it is also hereditary. We may give it a new name
“Polyandrism” or something else, but, in fact, there is no essential distinction of this kind of re-
version from peloria.
It deserves mentioning that most of the regular-flowered entities, including primitive, ad-
vanced and peloric ones, occur in Asia and Australasia, where the Orchidaceae may have ori-
ginated as pointed out by some botanists. We have good reason to verify the primitiveness and
normality of many regular-flowered entities, but there exists no sufficient evidence for the im-
possible existances of normally regular-flowered species in those like Dendrobium, Eria, Lecanor-
chis, etc. For instance, Lecanorchis javanica, Dendrobium atavus and the new species described
here are considered to be peloric forms, but it is only a conjecture, for no reason can be given
for it. It is not impossible that some so-called peloric forms may prove to be truly primitive ones
in the future. Of course, a closer investigation is needed.
Summarizing the above, we may come to the following conclusions:
1. Regular or nearly regular perianth is a normal characteristic of orchids. It is chiefly
found in some primitive taxa and sometimes also in certain peloric forms and advanced groups.
Regular-flowered entities may not necessarily be peloric forms.
2. There exist two different types of peloria in Orchidaceae. One is abnormal form, with
its peloric flowers appearing at random. The other is “normal” form, with its individuals all
possessing peloric flowers. The latter is inheritable and can produce seeds efficiently, It would
be best to treat it as an independent species taxonomically, especially when its origin is uncertain.
3. Although peloria has been considered to he a reversal as a whole, conditions vary from
plant to plant. Some peloric forms have petal-like lip, and others have labellum-like petals.
Sometimes the same plant produces different kinds of peloric flowers in different years, sometimes
peloric flowers do not reappear upon the same plant. A few species can produce both peloric
and normal individuals, but others produce peloric forms only. Peloria is in fact a term only
used to cover the phase in which lip becomes similar to the petals. It is never all-embracing.
We recognize the existance of peloria in Orchidaceae, but great care must be taken to distinguish
truly peloric form from normally primitive one. It must be admitted that what causes peloria
and even what is peloria are still problems awaiting solution.
Acknowledgments: Our heartfelt thanks are due to Dr. Leslie A. Garay, Curator of the
Orchid Herbarium of Oakes Ames, Botanical Museum of Harvard University, for his valuable
suggestions during the preparation of this paper. We are also indebted to the artists, Mrs. Chun-
rung Liu and Mr. Chao-zhen Ji of our department, for their preparing the fine drawings.

No comments:

Post a Comment

recent post