The taxonomy of the fern genus Arachniodes Blume in China is rather complicated with the creation of many new names since the 1960's. The purpose of this article is to make a clarification of the genus as a whole from China and provide an enumeration of what is known at present. Through herbarium studies and field observations, the distribution, morphological criteria and subdivision of the genus Arachniodes from China are discussed. The total number of species has been reduced from ca 130 names to 58 names, some of which are still in need of studies to prove their acceptance. A subdivision of four sections is adopted and further completed, i.e. sect. Cavaleria, sect. Globisorae, sect. Amoenae , and sect. Arachniodes; and for the 50 species names included in the section Arachniodes, 10 species groups were proposed for the purpose of further comparison. Names of taxa that belong to Arachniodes known from China are enumerated in alphabetical order with information about their synonyms, their distribution and the sections and groups in which they are categorized.

Chromosome behavior during meiosis of the tetraploid Isoetes sinensis was observed to be similar to that of basic diploid Isoetes species. This observation was consistent with the previous report that polyploid species of Isoetes are allopolyploids. Meiosis was generally similar in both megaspore and microspore mother cells, but differences were observed. Due to the smaller size of the microspore mother cells, during prophase I, chromosomes are not as dispersed as those in megaspore mother cells. Cytomixis was observed in all stages of meiosis in microspore mother cells, but it was not seen at any stage of meiosis in megaspore mother cells. Cytomixis, lagging chromosomes, chromosome bridges, chromosome fragments, and micronuclei, observed during meiosis in I. sinensis, can affect sexual reproduction, but it does not appear to be a major cause of population decline in this species. The major cause of decline is habitat degradation from human disturbance. The few remaining populations of the Chinese quillwort are fragmented and the numbers of individuals contained in these populations dwindle as a result of habitat degradation. Conservation efforts are needed to save I. sinensis from extinction.

Isoëtes is an ancient lycopod lineage with a highly conserved morphology that provides few morphological characters to resolve the phylogeny of its species. Species appear to have evolved by divergence and allopolyploidy. The basic diploids I. hypsophila, I. taiwanensis, and I. yunguiensis and the tetraploid I. sinensis occur in China. Analysis of ITS sequences indicates that the Chinese Isoëtes species are part of an Australasian clade including I. brevicula from Western Australia and I. kirkii from New Zealand. Two distinct cloned sequences of the second intron of a LEAFY homolog were recovered from I. sinensis supporting the hypothesis that I. sinensis is an allotetraploid. One of the I. sinensis cloned sequences was similar to the I. taiwanensis sequence and the other cloned sequence was similar to the I. yunguiensis sequence identifying I. taiwanensis and I. yunguiensis as the likely parents of I. sinensis. Other cloned sequences recovered from I. sinensis were recombined parts of the two distinct sequences. Morphological evidence supporting an allotetraploid origin of I. sinensis is found in its larger microspore size and intermediate megaspore texture compared to I. taiwanensis, and I. yunguiensis.