_??_1990 by Cytologia, Tokyo Cytologia 55: 553-570 , 1990

Biosystematic Studies on the (Compositae-Lactuceae) II. Karyological analyses

Jae-Hong Pak1 and Shoichi Kawano2

1 Department of Botany, Faculty of Science , Kyoto University, Kyoto 606, 2Department of Botany , Faculty of Science, Kyoto University, Kyoto 606, and Institute of Genetic Ecology, Tohoku University, Sendai 980, Japan

Accepted April 20, 1990

Earlier karyological studies of the genus Ixeris and related groups are represented by those of Ishikawa (1921) and Babcock et al. (1937) (also cf. Takemoto 1954, 1956, 1962, 1970, Nisioka 1956, 1960, 1963, Fujishima 1984). Ishikawa (1921) studied the chromosome numbers of 20 species from Japan, and showed that Lactuca (sensu Bentham and Hooker 1873, cum Ixeris) comprises some heterogeneous groups, with four different basic chromosome numbers, x=5, 7, 8 and 9. He further pointed out that the basic chromosome numbers and size are important criteria for the delimitation of the genera and assessment of the species relationships in Lactuca s. lat., demonstrating that those with x=5, 7, 8 and 9 base numbers are in good agreement with Nakai's generic concept (1920): (x=5), Paraixeris (x=5), Ixeris (x=7, 8), and Lactuca (x=9). However, later on Babcock et al. (1937), on the basis of an ex tensive karyological study of Crepidinae, claimed that the genus Ixeris (sensu Stebbins 1937) consists of the species with three different basic chromosome numbers, x=5, 7 and 8, which contradicts Ishikawa's viewpoint (1921). The genus Ixeris (Compositae-Lactuceae) is at present known to comprise about 20 species (Nakai 1920, Kitamura 1956, 1981) or 50 species, including some species of Crepidiastrum, Paraixeris and even Lactuca (Stebbins 1937, Tomb 1977). However, as stated above, the overall systematic status of the species referred to the genus Ixeris is still uncertain, and thus the de limitations of Ixeris and allied genera are still quite controversial. The objective of the present series of biosystematic studies is, first, to investigate more thoroughly karyological features of the referred to Ixeris based upon modern techniques, and second, to contribute to a better understanding of the species relationships and generic delimitations of Ixeris and allied genera. In this paper, we report the chromosome numbers and karyotypes of 1 I species and 5 subspecies, representing all 5 sections of Ixeris (sensu Kita mura 1956), collected from various localities in Japan, and ; six of these species have not been karyologically well known previously (Table 1). Furthermore, in order to evaluate more precisely the data on chromosome morphology, resting nuclei were critically ex amined on diploid species, and compared with one another.

Materials and methods

The taxa studied, sampling sites, and habitat conditions are all given in Table 1. Materials used for karyological studies were cultivated in pots in the greenhouse of the Department of

Botany, Kyoto University. The somatic chromosomes were observed in the root tip cells of more than 5 individual plants per population. The root tips were pretreated with a mixture of 3 parts of 0.002 mol 8-hydroxyquinoline and 1 part of 0.005% colchicine at 18-20•Ž for 2 hours and 40 minutes, and fixed in 45% acetic acid for 10-15 minutes at 4-8•Ž. Subsequently,

1 Present address: Department of Biology, College of Natural Science, Kyung-Pook National Univer sity, Taegu 702-701, Korea. Table 1. Localities, habitats of sampling sites, and the chromosome numbers of the genus Ixeris species examined in this study 1) Sectional classification followed Kitamura (1956). 2) The somatic chromosome numbers were examined for the first time, 3) The karyotypes were first described. 4) Voucher specimens certified by the authors. 556 Jae-Hong Pak and Shoichi Kawano Cytologia 55 the root tips were macerated in a 1:2 mixture of 45% acetic acid and 1 N HCl, stained with 1 aceto-orcein for 15 minutes, and then squashed. The karyotypes were arranged according to Levan et al. (1964) based on the positions of the centromere and their arm ratios. The de scriptions of resting nuclei followed Tanaka (1971). The voucher specimens are all preserved in the Herbarium of the Department of Botany, Kyoto University (KYO).

Results

1. Morphology of resting nuclei and prophase chromosomes Two types of resting nuclei and prophase chromosomes were found in Ixeris.

Fig. 1. Photomicrographs of resting nuclei and prometaphase chromosomes. A, B, Ixeris

repens. C, D, I. longirostrata. E, F, I. chinensis. G, H, I. stolonifera. I, J, I. tamagawaensis. K, L, I. polycephala. Scale equals 3ƒÊm.

1) X=8 group The basic chromsome number of Ixeris repens, I. stolonifera, I. longirostrata, I. polycephala, I. tamagawaensis and I. chinensis was x=8. Their resting nuclei consisted of many dark stained, round or rod-shaped condensed bodies (Fig. 1-A, C, E, G, I, K). The regions sur rounding these bodies were smooth and stained evenly. Thus, this feature corresponds to the rod or round prochromosome type (Tanaka 1971). Prophase somatic chromosomes were differentiated clearly into early condensing and late condensing parts. Their condensation begins at the proximal part of both arms (Fig. 1-B, D, F, H, J, L). 1990 Biosystematic Studies on the Genus Ixeris II 557

2) X=7 group The basic chromosome number of Ixeris dentata, I. laevigata, I. transnokoensis and I. makinoana was x=7. Their resting nuclei consisted of many small condensed bodies in the whole region of the nucleus (Fig. 2-A, C, E, G). This corresponds to the diffuse type (Tanaka

Fig. 2. Photomicrographs of resting nuclei and prometaphase chromosomes. A, B, Ixeris dentata. C, D, I. transnokoensis. E, F, I. laevigata. G, H, I. makinoana. Scale equals 3ƒÊm. 558 Jae-Hong Pak and Shoichi Kawano Cytologia 55

1971), as was shown in the Ixeris dentata complex by Fujishima (1984). No clear distinction can, however, be made between early condensing and late condensing parts in prophase. The condensation gradually proceeds from proximal to distal parts (Takemoto 1962) (Fig. 2-B, D, F, H).

Fig. 3. Photomicographs of mitotic metaphase chromosome. A, Ixeris repens. B, I. longiro strata. C, L. stolonifera. D, I. polycephala. E, I. tamagawaensis. F, I. debilis. G, I. chinensis

ssp. chinensis. H, I, I. chinensis ssp. strigosa. Arrows indicate secondary constrictions. Scale equals 3ƒÊm. 1990 Biosystematic Stidues on the Genus Ixeris II 559

2. Somatic chromosome numbers and karyotype constitutions Differences in basic chromsome numbers, i.e., x=7 and 8, are also reflected in the dif ferences of total genome size and the length of each chromosome complement. The total genomic size of the x=8 group varied from 25.2ƒÊm to 37.3ƒÊm: Ixeris repens (35.5ƒÊm), I.

Fig. 4. Photomicographs of mitotic metaphase chromosome. A, Ixeris dentata ssp. nipponica. B, I. dentata ssp. dentata. C, I. dentata ssp. alpicola. D, I. makinoana. E, I. laevigata. F, I. transnokoensis. Arrows indicate secondary constrictions. Scale equals 3ƒÊm. 560 Jae-Hong Pak and Shoichi Kawano Cytologia 55 stolonifera (37.3ƒÊm), I. longirostrtaa (30.3ƒÊm), I. polycephala (29.3ƒÊm), I. tamagawaensis

(25.2ƒÊm), I. chinensis (30.1ƒÊm). The chromosome length of the x=8 group ranged from 1.2ƒÊm to 3.7ƒÊm (Figs. 3, 5). The total genome size of the x=7 group was much larger, ranging from 43.2ƒÊm to 70.9ƒÊm: Ixeris dentata complex (61.0-70.9ƒÊm), I. laevigata (61.6ƒÊ m), I. transnokoensis (66.3ƒÊm), I. makinoana (43.2ƒÊm). The chromosome length of the x=7 group ranged from 2.2ƒÊm to 6.5ƒÊm (Fgs. 4, 6, 7). (1) Ixeris repens 2n=16 (Figs. 3A, 5A, 8A) This is a typical species found on coastal sandy beaches. Five different materials collected from Shiraoi in Hokkaido, Toyocho in Kochi, Hamatsume in Kyoto, and Kampo and Dalri Island, Korea, were karyologically examined. All the plants examined proved to possess the somatic chromosome number of 2n=16. This number was in agreement with that reported by Jinno (1953), Asano (1960) and Nishikawa (1984). Ishikawa (1921, as Lactuca repens) also reported the haploid chromosome number of n=8 (Table 1). The karyotype of this species is described for the first time in this study (Figs. 3A, 6A). The chromosome complement consisted of six median (Nos. 1-5, 8) and two submedian pairs (Nos. 6, 7). The first and eighth pairs were heterozygous regarding the satellite at the distal portion of their short arms. (2) Ixeris polycephala 2n=16 (Figs. 3D, 5B, 8B) Ixeris polycephala is an annual species which grows mainly in crop gardens and/or at the edge of fields. Two populations from Kyongju and Chuhulsan in Korea were examined. All materials had the somatic chromosome number of 2n=16. Ishikawa (1921, as Lactuca ma tsumurae) and Shetty (1967) reported that the haploid chromosome number was n=8 in plants from Japan and (Table 1). The chromosome complement was six median (Nos. 1-6) and two submedian pairs (Nos. 7, 8) (Figs. 5B, 8B). The largest pairs had satellites at the distal portion of their short arms (No. 1). The somatic chromsosome number and the karyo type of this taxon are reported for the first time in this paper. (3) 2n=16 (Figs. 3C, 5C, 8C) This is a typical species of the open grassy slopes as well as on foothills along roadsides in the lowlands. Materials collected from three different populations, i.e., Hieizan, Takinoike and Garyusan in central Honshu, were examined. All the materials turned out to possess 2n=16 somatic chromosomes. The results are in agreement with those of the previous reports (Babcock et al. 1937, Takemoto 1952, Lee 1971, Nishikawa 1979). Ishikawa (1911, 1916, 1921, as Lactuca stolonifera) reported its haploid number as n=8 (Table 1). The somatic chromo some complement of the materials examined consisted of six median (Figs. 5C and 8C, Nos. 1-5, 8) and two submedian pairs (Nos. 6, 7). The first and eighth pairs had satellites at the distal portion of their short arms. These chromosome pairs were heterozygous as to the satellite. However, Takemoto (1952) did not describe any satellites. (4) Ixeris debilis 2n=48 (Figs. 3F, 5D) This is a common weed of old fields and vacant lots. Plants collected from four popula tions, i.e., Hieizan in Kyoto, central Honshu, the Iriomote Island of Okinawa, and Masan and Dalri Islands in Korea, were examined. All materials examined had a hexaploid somatic chromosome number of 2n=48 (Fig. 5D). This result agrees with the previous report by Takemoto (1952). Ishikawa (1916, as Lactuca japonica) reported the haploid chromosome number of n=24, but a different haploid number of n=12 was also reported from the plants of Yehliu and Tanshui in Taiwan (Hsu, 1970) (Table 1). The chromosome complement con sisted of 36 median and 12 submedian chromsomes (Fig. 5D). The first and eighth pairs were heterozygous as regards the satellite at the distal portion of their short arms (Fig. 5D, Nos. 1, 8). The karyotype observed in this study was slightly different from that of Takemoto (1952), who did not describe any satellite chromosomes. Takemoto (1952) also concluded that I. debilis (as I. japonica) may be an autohexaploid derived from I. stolonifera, based on a com 1990 Biosystematic Studies on the Genus Ixeris II 561 parison of both karyotypes. However, it was confirmed by Pak and Kawano (in press) that I. debilis exhibits a greater similarity to I. polycephala in the fruit wall anatomy than to I. stolonifera.

Fig. 5. Karyotypes at mitotic metaphase of the x=8 group. A, Ixeris repens. B, I. poly cephala. C, I. stolonifera. D, I. debilis. E, I. longirostrata. F, I. tamagawaensis. G, I. chinen sis ssp. chinensis. H, I, I. chinensis ssp. strigosa. Scale equals 3ƒÊm. 562 Jae-Hong Pak and Shoichi Kawano Cytologia 55

(5) Ixeris longirostrata 2n=16 (Figs. 3B, 5E, 8D) This endemic species of the Bonin Islands occurs primarily on more or less open grassy slopes near the sea coast. The somatic chromosome numbers of the plants collected from Nankinhama of Hahajima, and from Minamijima, an islet off Chichijima, were 2n=16. This result was in agreement with the previous report by Ono and Masuda (1981) (Table 1). The chromosome complement consisted of six median (Nos. 1-6) and two submedian pairs (Nos.

Fig. 6. Karyotypes at mitotic metaphase of the x=7 group. A, Ixeris dentata ssp. dentata f.

amplifolia. B, I. dentata ssp. nipponica. C, I. dentata ssp. kitayamensis. D, I. dentata ssp. alpicola. E, I. laevigata. F, 1. transnokoensis. G, I1. makinoana. Scale equals 3ƒÊm.

7, 8), of which the first median pairs had satellites at the distal portion of their short arms (Figs. 5E, 8D). Ono and Masuda (1981) reported a slightly different karyotype for the plants collected from Mukojima which is situated in the north of Chichijima. The somatic chromo some complement consisted of two large median pairs and six submedian pairs. (6) Ixeris tamagawaensis 2n=16 (Figs. 3E, 5F, 8E) The habitat of this endemic species in Honshu is in the flood plain of rivers. Materials collected from populations in Matsumoto and Togakushi, both in Nagano Prefecture, had the 1990 Biosystematic Studies on the Genus Ixeris II 563

somatic chromosome number of 2n=16. The present result was in agreement with that of Nisioka (1956). Ishikawa (1916, 1921, as Lactuca tamagawaensis) reported the meiotic chro mosome number of n=8 for this (Table 1). The somatic chromosome complement consisted of five pairs (Nos. 1-5) with median constriction (Figs. 5F, 8E) and three pairs (Nos. 6-8) with submedian constrictions. Only one chromsome of the first and eighth pairs had a satellite on the terminal portion of their short arms, and thus they were heterozygous. However, Nisioka (1956) reported a homozygous karyotype in the plants collected from Tama gawa in Tokyo. (7) Ixeris chinensis complex i) I. chinensis ssp. chinensis 2n=16 (Figs. 3G, 5G, 8F) This subspecies widely occurs in northeastern continental and Taiwan, and is a com mon ruderal of the sunny roadsides. Plants from three populations in Korea (Kyongju, Kayasan, and Palgongsan) were examined. The somatic chromosome numbers were all 2n= 16 (Figs. 5G, 8F), as reported in a previous study (Peng and Hsu 1978). However, dif ferent haploid chromosome numbers have been reported for this subspecies: n=6 from Tawu (Hsu 1970) and Yehliu (Hsu 1970), n=7 from Yanmingshan (Chuang et al. 1962), x=9 and 2n=18 from Wulai (Hsu 1967) and n=12 from Yushan-chienshan (Hsu 1970) in Taiwan (Table 1). The somatic chromosome complement of all materials examined in the present study consisted of five median and three submedian pairs (Figs. 5G and 8F, Nos. 1-5, 6-8). The first pair had a small satellite at the distal portion of their short arms. ii) I. chinensis ssp. strigosa 2n=24, 32 (Figs. 3H and I, 5H and I) Samples were taken from two populations, at Kyongpook University in Taegu and Kwang nung in Seoul, Korea. The plants from Taegu turned out to be a triploid with 2n=24 somatic chromosomes (Fig. 5H), which is a new number for this taxon. Among the chromosome complement, the largest chromosomes had a satellite at the distal portion of their short arms, and the eighth sets were heterozygous, only two chromosomes having a satellite at the distal position. All the plants from Kwangnung had the somatic chromosome number of 2n=32, thus being tetraploid. The tetraploid number for this taxon is in agreement with the report of Babcock et a1. (1937, as I. chinensis). Ishikawa (1921, as Lactuca chinensis) also reported the haploid chromosome number of n=16 (Table 1). The first and eighth pairs of these tetra ploid plants heterozygously had two satellites at the distal portion of their short arms (Fig. 51). The karyotype for this taxon is described for the first time in this study. It now became evident that the karyotype of Ixeris chinensis ssp. chinensis is very similar to that of I. chinensis ssp. strigosa in both triploid and tetraploid plants. However, polyploid plants with pale purplish ligules possessed heterozygous chromosome pairs regarding to satel lites, and thus these triploid and tetraploid plants may not be of simple autopolyploid origin. 8) The Ixeris dentata complex This complex extends widely from the lowlands up to the alpine zone of high mountains in Japan. Eleven different cytotypes were recognized in this complex; namely, diploid (2n=14; Figs. 4A, 6A and D), triploid (2n=21; Figs. 4B, 7A, C and F), and tetraploid (2n=28; Figs. 4C, 7B and G) were found in both ssp. dentata and ssp. alpicola, but diploid (2n=14; Fig. 6C) and triploid (2n=21; Fig. 7D) were found in ssp. kitayamensis. Only diploid occurred in ssp. nipponica (2n=14; Fig. 6B), while triploid was found from ssp. kimurana (2n=21 ; Fig. 7H). These results agree well with many previous reports (Okabe 1935, Takemoto 1954, 1956, 1962, 1970, Nisioka 1956, 1960, 1963, Fujishima 1984) (Table 1). The diploid and tetraploid forms of Ixeris dentata ssp. dentata mainly occur in the lowland populations. The diploid form (2n=14; Fig. 6A) of ssp. dentata f. amplifolia was discovered in plants from Kirin zan, Niigata Prefecture, whereas the tetraploid form of ssp. dentata was found in those which were collected from Shinshiro in Aichi Prefecture in Japan, and also Masan in Korea. Ko 564 Jae-Hong Pak and Shoichi Kawano Cytologia 55 yama (1978) previously postulated that the occurrence of a tetraploid form in the lowland populations based upon his pollen study. i) Diploid form (2n=14) a) Ixeris dentata ssp. dentata .f. amplifolia (Figs. 6A, 8G) b) I. dentata ssp. nipponica (Figs. 4A, 6B, 8H)

Fig. 7. Karyotypes at mitotic metaphase of the x=7 group. A, B, Ixeris dentata ssp. dentata.

C, I. dentata ssp. dentata var. albiflora. D, I. dentata ssp. kitayamensis. F, G, I. dentata ssp. alpicota. H, I. dentata ssp. kimurana. Scale equals 3ƒÊm.

c) I. dentata ssp. kitayamensis (Figs. 6C, 8I) d) I. dentata ssp. alpicola (Figs. 6D, 8J) No difference can be recognized in the karyotypes of the diploid forms (Figs. 6A, B, C, D). The chromosome complement consists of five median (Nos. 1-5) and two submedian pairs (Nos. 6. 7), of which the largest chromosome pair (No. 1) has satellites at the distal portion 1990 Biosystematic Studies on the Genus Ixeris II 565

Fig. 8. Idiograms of haploid chromosomes at mitotic metaphase. A, Ixeris repens. B, I. polycephala. C, I. stolonifera. D, I. longirostrata. E, I. tamagawaensis. F, I. chinensis. G, I. dentata ssp. dentata f. amplifolia. H, I. dentata ssp. nipponica. I, I. dentata ssp. kitayamensis. J, I. dentata ssp. alpicola. K, I. laevigata. L, I. transnokoensis. M, I. makinoana. 566 Jae-Hong Pak and Shoichi Kawano Cytologia 55

of their short arms. The above results coincide well with those of the previous studies (Take moto 1956, 1962, 1970, Nisioka 1956, 1960, 1963). Ishikawa (1921) reported the haploid num ber of n=7 from ssp. alpicola (as Lactuca alpicola). ii) Triploid form (2n=21) a) Ixeris dentata ssp. dentata (Figs. 4B, 7A) b) I. dentata ssp. dentata var. albiflora (Fig. 7C) c) I. dentata ssp. kitayamensis (Fig. 7D) d) I. dentata ssp. alpicola (Fig. 7F) e) I. dentata ssp. kimurana (Fig. 7H) Ssp. dentata, (incl. f. atropupurea, var. albiflora, f. amplifolia, var. stolonifera), ssp. shiranen sis, ssp. kimurana, ssp. alpicola, and ssp. kitayamensis have hitherto been known as triploid races (Okabe 1932, Nisioka 1956, 1960, 1963, Kawano 1961, Takemoto 1956, 1962, 1970, Fujishima 1984) (Table 1). Among the triploid races studied, ssp. alpicola and the other four taxa had the karyotypes referred to K11 type and K1 types sensu Fujishima (1984), respectively. iii) Tetraploid form (2n=28) a) Ixeris dentata ssp. dentata (Fig. 7B) b) I, dentata ssp. alpicola (Fig. 4C, 7G) Ssp. kimurana and ssp. alpicola have hitherto been reported as tetraploid races (Okabe 1935, Nisioka 1963, Takemoto 1962, 1970, Fujishima 1984). Ssp. dentata collected from the lowlands in Shinshiro, Aichi Prefecture, Honshu, and Masan in Korea had the somatic chromo somes of 2n=28. The first chromsome set had only two chromosomes with satellites at the distal portion of their short arms (Fig. 7B). Ssp. alpicola collected from the alpine zone of Mt. Senjogadake had 2n=28 chromosomes. The chromosome complement of this material was heterozygous, only three chromosomes of the first chromosome set having the satellites at the distal portion of the short arms (Fig. 7G).

(9) Ixeris laevigata 2n=14 (Figs. 4E, 6, 8K) This species is mainly distributed in the subtropical regions of Asia (Koster 1976). The individuals collected at Pinglin in Taiwan, and Kawagishi-cho in Kagoshima Prefecture, Kyushu, had 2n=14 somatic chromosomes. The present result was in agreement with those of the previous reports (Chuang et al. 1962, Hsu 1970, Peng and Hsu 1978), although 2n=16 is also known from this taxon (Hsu 1967) (Table 1). The chromosome complement was com

posed of six median pairs (Nos. 1-4, 7) and one submedian pair (No. 6) (Figs. 6E, 8K). The sixth submedian pair had secondary constrictions at the distal position of the long arms. The first large median (5.9ƒÊm) and the sixth pair are characteristic of the chromosome com plement of I. laevigata. The karyotype for this taxon was first described in this study. (10) Ixeris transnokoensis 2n=14 (Figs. 4F, 6, 8L) This endemic species of Taiwan was collected from Mt. Noko. Its somatic chromosome number proved to be 2n=14. Hsu (1970) reported the haploid number of n=12 on the material collected at Yushan-chienshan in Taiwan (Table 1). But, judging from his voucher specimen, the plant he examined obviously belongs to I. chinensis (cf. Peng and Hsu 1978). The chro mosome complement consisted of six median pairs (Nos. 1-5 , 7) and one submedian pairs (No. 6) (Figs. 6F, 8L). The first large (6.1ƒÊm) median and the sixth pair possessed the secondary constriction at the distal portion of the long arms. The present count and the karyotype represent a new report for this taxon. (11) Ixeris makinoana 2n=14 (Figs. 4D, 6G, 8M) This species is widely distributed from the Himalayas through to southern Japan . The material was collected in a small population in Akou, Hyogo Prefecture, which occurred in the wet site near the pond. The somatic chromosome number of this material was 2n=14 . The chromosome complement consisted of four median (Nos. 1-4) and three submedian pairs 1990 Biosystematic Studies on the Genus Ixeris II 567

(Nos. 5-7) (Figs. 6G 8M). The first median pair (4.0ƒÊm) was larger than any of the other pairs, the sixth submedian pairs having secondary constrictions at the distal portion of their long arms. The present count and the karyotype represent a new report for this taxon.

Discussion

In revising taxonomically the genus Ixeris s. lat., Nakai (1920) established three genera Ixeris, Crepidiastrum and Paraixeris based on habitual characters and achene morphology: Ixeris is a herb with erect or long creeping stems, and possesses achenes with long beaks and 10 ribs on the surface; Crepidiastrum has shrubby growth habits, and produces achenes lacking a beak and less prominent ribs on the surface; Paraixeris is characterized by branching growth habits and achenes with short beak, 14(15) ribs on the surface, and deciduous pappus. Nakai's generic concept (1920), however, was not supported by Stebbins (1937), who concluded that Crepidiastrum and Paraixeris should be merged into Ixeris, and further considered that Ixeris (including Crepidiastrum and Paraixeris) constitutes a distinct group from Lactuca, Crepis, and (Bentham and Hooker 1873) on the basis of morphological features, such as habit (slender stems), entire leaves, fewer flowers per head, calyculated involucres, achenes (10 equal ribs), ovary (5 vascular bundles), and pappus (bristle). However, Kitamura (1956) emphasized the habitual differences recognized among the members of Ixeris sensu Stebbins (1937) as a character of diagnostic value, and defined the genus Ixeris in a narrower sense, ex cluding Crepidiastrum and Paraixeris, supporting the classificatory system proposed by Nakai (1920). Ishikawa (1921) observed the chromosome morphology of about 20 taxa of Lactuca s. lat. from Japan. He recognized five distinct groups among them: Lactuca sensu Nakai (n=9), Crepidiastrum sensu Nakai (n=5), Paraixeris sensu Nakai (n=5), Ixeris sensu Nakai (n=8), and Ixeris sensu Nakai (n=7). Although the fourth and fifth groups were referred to the genus Ixeris sensu Nakai, he suggested that they differ from each other in basic chromosome numbers and chromosome size: i.e., (1) an x=8 group which includes Ixeris repens (as Lactuca repens), I. stolonifera (as L. stolonifera), I. debilis (as L. debilis), I. polycephala (as L. matsumurae), I. tamagawaensis (as L. tamagawaensis) and I. chinensis ssp. strigosa (as L. chinensis); and (2) an x=7 group which comprises I. dentata ssp. dentata (as L. dentata var. thunbergii), I. dentata ssp. dentata var. albiflora (as L. dentata var. albiflora) and I. dentata ssp. alpicola (as L. dentata var. alpicola). Peng and Hsu (1978), who studied some Asteraceous species in Taiwan, suggested that Ixeris (I. chinensis, x=8; I. laevigata, x=7) should be segregated from Crepidiastrum (C. tai waniaum, 2n=10; C. lanceolatum, 2n=10) by the basic chromosome numbers. Ono and Masuda (1981) also proposed that Ixeris (I. longirostrata, 2n=16) could be separated from Crepidiastrum (C. ameristophyllum, 2n=10; C. grandicollum, 2n=10; C. linguaefolium, 2n= 10) by its different basic somatic chromosome number and karyotypes. However, Babcock et al. (1937) recognized three different basic chromosome numbers in Ixeris, i.e., x=5, 7, and 8. They considered x=8 to be the most primitive basic chromosome number in Ixeris because this number was encountered in half of the species studied (Stebbins et al. 1953). Comparing the somatic chromosome number and morphology of Ixeris sonchifolia sensu Nakai (="Ixeris denticulata ssp. sonchifolia") and Paraixeris denticulata sensu Nakai (="Ixeris denticulata ssp. typica"), they concluded that Paraixeris should be merged into Ixeris. In the present study, the authors examined additional four species of Ixeris which were not karyologically studied by Ishikawa (1921), i.e., Ixeris longirostrata, I. laevigata, I. transnoko ensis and I. makinoana. I. longirostrata proved to fall into the x=8 group, but all the others into the x=7 group. As was pointed out by Ishikawa (1921), it now is evident that the genus 568 Jae-Hong Pak and Shoichi Kawano Cytologia 55

Ixeris includes two distinct groups. Moreover, the morphology of both resting nuclei and prometaphase chromosomes was also found to be conspicuously different in these two groups with two different basic chromosome numbers, corresponding to prochromosome type (x=8) or diffuse type (x=7) (Tanaka 1971). The total chromosome length and relative chromosome size were clearly different in the two groups, which also indicates that these two groups have basically different karyotypes. The karyotypes of the x=8 group consist of 5 median and 3 submedian pairs, or 6 median and 2 submedian pairs, while those of the x=7 group are com posed of 4 median and 3 submedian pairs, 5 median and 2 submedian pairs, or 6 median and 1 submedian pairs. In short, species of Ixeris with two basic chromosome numbers have clear ly different chromosome morphology; i.e., the x=8 group is characterized by prochromosome type, small chromosomes and specific karyotype compositions of 5m+3sm or 6m+2sm; the x=7 group, by diffuse type, large chromosomes and karyotype compositions of 4m+ 3sm, 5m+2sm, or 6m+1sm. The overall differences between these two groups are found not only in chromosome morphology but also in fruit wall anatomy and its developmental characteristics; i.e., species of the x=8 group have winged achenes and those of the x=7 group, ribbed achenes (Pak and Kawano in press). They also differ in number of ligules per head and color of pappus: the x=8 group possesses 15-30 ligules per head and whitish pappus while the x=7 group has 5-12 ligules per head and brownish pappus. Considering all these features of the two groups, the species with x=7, which have been referred to sect. , no doubt represent a distinct phylogenetic group and thus should be grouped as an independent genus, i.e., Ixeridium, and the remainder of the species with x=8 should be referred to Ixeris s. str. (Pak and Kawano (1990a, b in press). As to the origin of the x=7 group of Ixeris, Babcock et al. (1937) postulated that the Ixeris dentata complex may have originated through intergeneric hybridization between the ancestral groups of Ixeris and Crepis, based on their growth habits, morphology of leaves and involucres, and cytological features, since some Crepis in section Ixeridopsis possess the same basic number (x=7) and similar chromosome size and morphology (also cf. Babcock 1947). Recently, Weber (1984) established a new genus Askellia, which included all species with x=7. These species were all those previously referred to Crepis section Ixeridopsis (Babcock 1947). One question arising here is the true affinity between the species of Ixeridium with x=7 and those of Askellia, which needs to be clarified in a future study. Another notable karyological feature of the x=7 group of Ixeris is that two subgroups can be further differentiated by their karyotype constitutions. The first subgroup is represented by the Ixeris dentata complex. Their karyotypes are composed of five median and two sub median pairs, of which the first, longest, median pair possesses a satellite at the distal portion of the short arm, and the seventh pair is submedian with short arms. The latter subgroup comprises I. laevigata, I. transnokoensis, and I. makinoana. The chromosome complements of these species consist of one large metacentric pair and the sixth pair with a secondary con striction at the distal portion of the long arms. The karyotypes of I. laevigata and I. trans nokoensis consisted of 6 median and 1 submedian pairs, and that of I. makinoana, of 4 median and 3 submedian pairs. Similar karyotypes of 1. laevigata, I. transnokoensis, and I. makinoana, all which are characterized by the first and sixth chromosome pairs, are not to be recognized in those of the I. dentata complex. Thus, I. laevigata, I. transnokoensis, and I. makinoana may be more closely related to one another than to the I. dentata complex. For elucidating the true affinities among the species of Ixeris, Ixeridium, Crepidiastrum , and other related groups in Crepidinae, further critical studies, including karyology and mole cular biological features, seem necessary. 1990 Biosystematic Studies on the Genus Ixeris II 569

Summary

Eleven species and five subspecies of the genus Ixeris s. lat. were karyologically investigated. Somatic chromosome numbers and karyotypes of Ixeris polycephala (2n=16), 1. chinensis ssp. strigosa (2n=24), I. transnokoensis (2n=14), and I. makinoana (2n=14) were examined for the first time. Further, the karyotypes of I. repens, I. chinensis complex, and 1. laevigata, were also described. As a result, plants with x=8 and small relative chromosome length, and those with x=7 and large relative length, were recognized in the genus. The former group possesses the rod or round prochromosome type of resting nuclei, but the latter has the diffuse chromo some type. These karyological features proved to be good criteria for defining Ixeris and other related genera, since they match very well with gross morphological as well as anatomical characters. The species of Ixeris examined thus were divided into two groups on the basis of chromosome morphology. The first group, with x=8 and similar karyotypes, is composed of I. repens, I. stolonifera, I. debilis, I. longirostrata, I. polycephala, I. chinensis complex and I. tamagawaensis. The second group, with x=7, comprises the I. dentata complex, I. laevigata, I. transnokoensis, and I. makinoana. In conclusion, the species with x=7, which have been referred to sect. Ixeridium, no doubt represent a distinct phylogenetic group, and should be separated from those with x=8 as an independent genus.

Acknowledgments

We are indebted to Mr. Hisao Nishimura, who patiently looked after our plants at green house of the Department of Botany, Kyoto University. We wish to thank Dr. Hiroshige Koyama, and Mr. Gen Murata for their helpful discussions during the course of this study. Our cordial thanks are due to Drs. Mitsuru Hotta, Jin Murata, Motomi Ito, Keiko Kosuge, Messrs. Takaya Yasui, Akihiko Makimoto, and Toshio Fujii for collecting the plants used in this study. We also would like to express our cordial thanks to Professor Shozo Noda for his invaluable comments and suggestions concerning karyological problems.

References

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