The Classification of the Cyatheaceae in China

Abstract

Abstract:

The family Cyatheaceae (s. str.) defined here is a group with scaly stems. The

classification of this scaly group has a long history, but views on the generic rank are contro-

versial. The division of three genera based mainly on indusia had lasted for almost one cen-

tury and was finally proved unnatural. Not all species lacking indusia are closely related to

each other. In other words, among the exindusiate species, some are closer to those of indusiate

species than to the other exindusiate ones, and vice versa. Obviously, the loss of indusia must

have taken place in different evolutionary lines. In the last few decades, Tryon (1970, 1982)

made a new chart on the basis of the structure of petiole scales, in which six scaly genera were

proposed, while Holttum (1957, 1963, 1974, 1981), with the emphasis on the chromosome number

n=69 in all species so far counted, insisted on one genus in a broad seuse, including two su-

bgenera and two sections in each subgenus.

After Chinese material has been studied, the author proposes several points as follows: 1)

It is acceptable that the family is divided into two main groups based on the structure of

petiole scales. New information from Chinese material supports this separation. Pneumathodes,

a kind of aerating tissue along lateral sides of raches and stipes, are of two forms. If they come

to the surface, the surface is broken and a row of fusiform holes emerge at the maturity, when

we call them open pneumathodes. If they do not come to the surface, no hole but a discontinous

whitish line apears on the surface, when we call them closed pneumathodes. These two

forms of pneumathodes are correlated with the two patterns of petiole scales. 2) Sporangia of

two kinds, producing 16 or 64 spores, occur in the family. For Chinese species, one group

is of 16-spored sporangia and is considered as a derivative, and the others are of 64-spored

sporangia as most ferns. 3) Among various forms of indusia, two evolutionary changes may

be traced. although the parallel development of indusia in different groups indicates that the

structure is not a useful systematic character for distinguishing genera. In one line the primi-

tive hemitelioid indusium fully developed finally forming a spherical one covering a whole

sorus, and in the other it simplified forming a scalelike indusium hidden by a mature sorus.

Perhaps, the loss of indusia results from simplifying.

Recognized in the present paper are 14 species and 2 varieties, which are grouped into

three taxa: Sphaeropteris, Alsophila and Gymnosphaera. Sphaeropteris, characterized by closed

pneumathodes and structurally conform petiole scales, is given the generic status. Alsophila

and Gymnosphaera are both with open pneumathodes and structurally marginate petiole scales,

but the former is with 16-spored sporangia, while the latter with 64-spored sporangia. They

are so closely related in morphology that they hardly merit generic rank, as compared with the

genus Sphaeropteris which has 64 spores in each sporangium. They are thus treated as two sub-

genera under the genus Alsophila.

Cyatheaceae has a pantropical distribution extending northwards to S. China and S. W.

China. Its northern limit in China is at the Huaying Mountain in Linshui County of Sichuan

Province, at about 30°N.

I am indebted very much to Prof. R. G. Ching and K. H. Shing for stimulating discussions

of the classification of Cyatheaceae, and also to Prof. W. M. Chu and H. S. Kung for very

helpful comments on the manuscript.

Key words: Cyatheaceae, Alsophila, Gymnophaera, Sphaeropieris, classification, distribution

Xia Qun. The Classification of the Cyatheaceae in China[J]. .

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The Classification of the Cyatheaceae in China

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