Abstract:

Cytological  and biosystematic studies on the genus Pteris  have  made  a  great

contribution to the theory of speciation and evolution in ferns. Sino-Japanese area is one of the

speciation centers of this genus. But only a few Chinese species have been known cytologically.

As a preliminary study, ten species of the genus Pteris and two species of the related genera

Pteridium and Histiopteris were observed.  All the materials were collected from southwest

and south China.  Their young sori were fixed in ethanol and glacial acetic acid (3:1), in the

field.  The preparations were made with acetocarmine squash method.  The vouchers are de-

posited in PE.

      The results of observation are summarized in Table 1. Of Pteris, four species are agamosp-

orous, eight are polyploid, six are actually the members of species complexes. Only two species

are purely sexual diploids.

     Pteris cretica L. var. nervosa (Thunb.) Ching et S. H. Wu has 58 autobivalents at meiosis

of spore mother cell, and usually produces 32 diplospores per sporangium.  It is obviously an

agamosporous diploid.  Apart from 32-spored sporangium, some 4-, 8-, 16-, 64-, 13-, 34-, 36-

spored, completely abortive or partly abortive sporangia were also found in the fixed material

of a single individual.  For explaining these unusual types of sporangia at least nine sporo-

genesis routes can be inferred.  It may not be impossible that besides mainly producing func-

tional diplospores, P. cretica var. nervosa also gives a few functional giant spores with a doubled

or multiplied somatic chromosome number, which means that polyploids may be simply derived

from the spores produced by their diploid parent.  The spores in a sporangium are usually

tetrahedral, but a few bilateral ones are also found in some sporangia.  Sometimes, the bila-

teral spores are even more than the tetrahedral ones in a sporangium.

     Pteris vittata L. from the type locality shows 58 bivalents at diakinesis of meiosis.  Without

doubt, it is a sexual tetraploid, which was also found in south Guangdong and south Yunnan.

However, Its natural ancestral diploid has been widely found in the subtropical regions of

China, such as Sichuan, Guizhou, Yunnan and Hubei provinces.  A sterile triploid with the

chromosome number of n=201Ⅰ+26Ⅱ+5Ⅲ and a sterile tetraploid hybrid with the chromosome

  number of n=9Ⅰ+45Ⅱ+3Ⅲ+21Ⅴ were found in south Yunnan and south Guangdong respec-

  tively.  It is evident that P. vittata L. sensu lato is a species complex which includes several cy-

  totypes.  Its hexaploid form was reported from south India by Abraham et al.  The distribu-

  tion pattern of different cytotypes in P. vittata complex may indicate that the tropics is more

  favourable to formation and surviving of polyploid than the subtropics.  However, it is most

  possible that Chinese subtropics is the origin place of the ancestral member in the P. vittata

 complex.  In gross morphology, the tetraploid and triploid forms are only bigger and stronger

 than the diploid form.  But the diploid can also grow rather big in cultivation.  They can har-

 dly be distinguished from each other.  Therefore, they are not given formal names here.  The

 author fully agree with Prof. T. Reichstein when he said in 1983 that it was hoped that a new

 nomenclature could be adopted for the cytotypes of species complex in future.

        The special chromosome number of Pteris deltodon Bak .was counted in this work for the

 first time.  It has 55 bivalents at meiosis of SMC.  This number is the only exception in the

 genus Pteris, and shows that aneuploidy may have taken place in this genus.  However, the pos-

 sibility can not be ruled out that P. deltodon is an allotetraploid came from two diploid spe-

cies respectively with the chromosome number 26 and 29.

       Pteris gallinopes described by Prof.  Ching in i983 is an agamosporous tetraploid with 116

 autobivalents at meiosis, different from the related triploid species P. dactylina Hook. and P.

henryi Christ.

       P. ensiformis Burm^。 P. muftifida Poir. and P. semipinnata L. are sexual tetraploids with

 n=58. P. excelsa Gaud. and P. oshimensis Hieron. var. paraemeiensis Ching are agamosporous

triploids with n = 87 autobivalents. P. wallichiana Agardh is a sexual diploid with n=29.

       The high frequency of polyploids and agamospory among these random sampled Chinese

species futher confirms the conclusion that both polyploidy and apomixis have played an im-

portant role in speciation and evolution of the genus Pteris.

        Pteridium aquilimum (L.) Kunh var. latiusculum (Desv.) Underw. ex Heller and His-

tiopteris incisa (Thunb.) J. Sm. have n=52 and n=96 respectively.  They are both sexual te-

traploids.  Their chromosome numbers show again that the genera Pteridium and Histiopteris

are distinquished from the genus Pteris by different basic numbers.

       This project is supported by the National Natural Science Foundation of China.