Cytological studies on three species of Gastrodia, myco-heterotrophic orchids, were carried out. Gastrodia gracilis had the chromosome number of 2n=22. The chromosome complement at resting stage showed the complex chromocenter type, and the metaphase chromosomes showed a bimodal karyotype in length consisted of two large chromosomes of 2.7 μm and 20 small ones varied from 2.1-1.1 μm. Gastrodia nipponica had the 2n=24 chromosomes showing the intermediate type between the simple chromocenter type and the complex chromocenter type at resting stage, and a gradual karyotype at metaphase chromosomes varied from 2.2-1.1 μm. Gastrodia flavilabella showed the 2n=26 chromosomes showing the intermediate type between the simple chromocenter type and the complex chromocenter type at resting stage, and a gradual decrease in size from the largest to the smallest chromosomes at metaphase varied from 1.6-0.9 μm. Thus, the different chromosome numbers existed in Gastrodia; 2n=22 in G. gracilis, G. confusa (Aoyama and Tanaka 1986) and G. pubilabiata (Nakata 2004); 2n=24 in G. nipponica; 2n=26 in G. flavilabella; 2n=36 in G. elata (Aoyama and Tanaka 1986), G. angusta (n=18, Liang 1984) and G. javanica (Aoyama and Yokota 2011).

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　Cosmos sulphureus Cav. was studied with respect to its meiotic behavior. It has been observed that this plant species is a diploid with the chromosome number of n=12. The course of meiosis was normal in most of the cells but some meiotic irregularities have also been observed.

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　Four species of Elsholtzia such as E. flava Benth., E. penduliflora W. Smith, E. ciliata (Thunb.) Hyl. and E. nipponica Ohwi had the common chromosome characters at the resting stage classified as the complex chromocenter type. Elsholtzia flava and E. penduliflora had the common chromosome number as 2n=20, while E. ciliata had the chromosome number of 2n=32 and E. nipponica had the chromosome number of 2n=16. The chromosome numbers of 2n=16 and 32 were considered diploid and tetraploid, respectively if the common basic chromosome number was x=8, while the chromosome number of 2n=20 could be diploid if the basic chromosome number was x=10, respectively. The chromosome numbers of 2n=20 for E. penduliflora and 2n=16 for E. nipponica were reported here for the first time. The karyotypes of the four species described here had commonly monomodal gradation in chromosome length from the largest to the smallest chromosomes, and showed median-, submedian- and subterminacentromeric chromosomes in E. flava and E. penduliflora, and median- and submedian-centromeric chromosomes in E. ciliata and E. nipponica.

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