A Primitive New Orchid Genus Tangtsinia and Its Meaning in Phylogeny

Abstract

Abstract:

Tangtsinia* S. C. Chen, a monotypic genus, is discovered in southeastern Szechuan

in China. It possesses a rather ordinary monocotyledonous habit, namely with a short

rhizome, non-thickend annual stem with scattered, spiral-arranged leaves and a terminal

inflorescence. Its habit somewhat similar to that of some very primitive genera, viz.

Apostasia, Tropidia, Cephalanthera and Selenipedilum, is of much morphological and

phylogenetic interest.

The primitive and significant floral features consist chiefly in the erect, hardly twisted

flower with nearly regular perianth and a unilocular ovary, in the column composed of

a terminal stigma and five small projections, in an erect anther with four naked pollinia,

and in the absence of the rostellum. Of special interest is the occurrence of five small

projections in the upper part of the column, and this is, however, a unique instance in

the family, including the Apostasieae. Among the five projections three are larger and

opposite to the petals respectively. Of these the two lateral ones bear a strong resem-

blance in texture to the two auricles in the Orchideae and some members of the Limo-

dorinae, which P. Vermeulen considered not as staminodia, but as appendages of the

single fertile stamen as usually seen in Allium. In the case of Tangtsinia, there exists the

third projection which, being situated in the front of the column and thus opposite to the

median petal (lip), shows no difference both in appearance and texture from the other

two. These three projections are at equal distance around the terminal stigma. In

view of these facts they can be no other organ than staminodia, representing the three

stamens of the inner whorl. And the other two smaller projections are also staminodia

which together with the single fertile stamen represent the outer whorl of three stamens.

Now it is safe to say that the two auricles existing in Cephalanthera, Epipactis and the

Orchideae are, in fact, also staminodia, representing the two lateral stamens of the in-

ner whorl. In consequence, there is fairly good reason to believe that the column in

Orchidaceae has developed from the union of six stamens and a central style, and this

is in agreement with the conclusion drawn by Swamy from vascular anatomy of orchid

flowers. Furthermore it is also an interesting fact that the pollen grains in this genus,

like those of Cephalanthera, Pogonia (sensu stricto), Aphyllorchis and some species of

the Vanillinae, are single, while in the vast majority of the Orchidoideae they are united

into tetrads. This feature, as well as the texture of pollen grains, is of considerable

significance in the classification and phylogeny of Orchidaceae.

On the basis of its morphological characters mentioned above, the present genus is

evidently one of the most primitive types in the subfamily Orchidoideae. It bears a

strong resemblance both in habit and floral features to Cephalanthera, especially C. falcata

(Thunb.) Bl. The relationship between these two genera is apparently much closer to each

other than to any of other existing primitive orchids. In addition, the similarity in some

of significant floral characters between Tangtsinia and the saprophytic Aphyllorchis, especi-

ally in the nearly regular perianth and a subterminal stigma of A. simplex Tang et

Wang, indicates their close relationship. It is quite possible that Cephalanthera and

Aphyllorchis are derived from Tangtsinia or Tangtsinia-like ancestor. Thus, Tangtsinia

is here placed as the most primitive genus in the Limodorinae. Furthermore this new

genus likewise shows more or less close affinity to Neottia, probably through N. gaudis-

sarti Hand.-Mzt., in which the flowers consist of nearly regular perianth and a very

primitive column with a terminal stigma and without the rostellum. On the other hand,

in comparing Tangtsinia with the Apostasieae, there occurs also some similarity, but a

closer investigation of their ovaries, perianthes, stigmas and some other features indicates

that there is little evidence of close or direct relationship between these two taxa, al-

though both are the ancestral types in this large family. The probable relationships be-

tween Tangtsinia and its allies may be diagrammed as follows:

With regard to the pollination, Tangiorchis is found to be self-pollinated. In the great

majority of cases, its flowers do not open at all, and none of which has been seen to be

visited by any insects. It is interesting to note that in almost all nearly faded flowers

examined by the writer the bases of the pollinia together with the base of the anther have

become attached to the stigma of the same flower, and thus self-pollination has taken

place. This type of pollination might be comparable with that of Cephalanthera dama-

sonia Druce.

Finally the writer should say something about its geographical distribution. This mo-

notypic genus is confined to Gin-fu-shan (Mt. Gin-fu) and its adjacent region in Nan-

chuan District of southeastern Szechuan, where it occurs at scattered points within an area

of no more than 250 square km. at an altitude between 700-2100 m. In view of its mor-

phology, pollination and geographical distribution, Tangtsinia might be an ancestral relic of

the family Orchidaceae and would give a possible clue as to the origin of this complicated

family.

Chen Sing-Chi. A Primitive New Orchid Genus Tangtsinia and Its Meaning in Phylogeny[J]. .

A Primitive New Orchid Genus Tangtsinia and Its Meaning in Phylogeny

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