_??_1993 The Japan Mendel Society Cytologia 58: 439-444 , 1993

Cytotaxonomic Studies of the Subtribe Pogostemoninae sensu Bentham (Labiatae) from South

Mariamma Cherian and P. I. Kuriachan

Department of Botany, University of Kerala , Kariavattom, Trivandrum -695581, India

Accepted August 4, 1993

The subtribe Pogostemonae of the tribe Satureineae (correct names: Pogostemoninae and Mentheae-Sanders and Cantino 1984) in Bentham's (1876) classification comprises of four genera and 63 species. The taxonomic position of the members of this subtribe has been the subject of several studies (Bentham 1832-36, 1876, Baillon 1892, Briquet 1895-97, Endlicher 1836-40, Erdtman 1945, Wunderlich 1963). However, chromosome numbers in only 12 of these species belonging to three genera are so far known (Mehra and Gill 1968, Bolkhovskikb et al. 1969, Gill 1971, Goldblatt 1981, 1983, 1985, 1988, Bir and Saggoo 1985, Cherian and Kuriachan 1981) and the systematic position of Pogostemoninae has not been examined from a cytotaxonomic angle. Nearly 23 species belonging to Pogostemon, Eusteralis and Colebrookea are known to occur in S. India (Gamble 1924). Cytological data of 11 of these along with a cytotaxonomic note are reported here.

Materials and methods

The source localities and voucher numbers of the various species reported here are given

in Table 1. Voucher specimens of the are preserved in KUBOT. Root tips for mitotic

chromosome studies were treated with 0.002M 8-hydroxy quinoline at 4•Ž for 3 hr prior to

fixation. Young flower buds and the root tips were fixed in a mixture of ethanol, acetic acid and

chloroform (3:1:1) and squashed in 1% acetocarmine.

Results

The chromosome counts studied are listed along with previous reports in Table 1 and

illustrated in Figs. 1-21. Chromosome numbers in Pogostemon gardneri (n=16), P. mollis

(2n=32), P. wightii (2n=32 and 64), Eusteralis stellata var. roxburghiana (n=14) and E. tomentosa var. gracilis (2n=32) are reported here for the first time. P. heyneanus (2n=64) and P. purpurascens (2n=34) are new records for the species, while P. benghalense (2n=64) is

reported from South India for the first time. All the species showed normal anaphase

separation and very low pollen sterility ranging from 1.7 to 15 per cent. Mitotic chromosomes

were observed in seven taxa. The chromosomes in all these species were small, from 0.67ƒÊm

to 2.00ƒÊm length and almost rod shaped. The primary constrictions were not clearly visible.

Discussion

Gill (1971) and Vij and Kashyap (1976) suggested x=8 as the basic number of Pogoste mon where as Saggoo and Bir (1985) reported that x=16 and 17 are its basic numbers. The chromosome numbers are reported in only 12 species of this genus. These showed n=16 or 17 or multiples of 16 (Mehra and Gill 1968, Gill 1971, Vij and Kashyap 1976, Krishnappa and Indiramma 1982, Saggoo and Bir 1981, Cherian and Kuriachan 1981, Present study). Among Table 1. Localities, chromosome numbers, chromosome size and previous reports in 11 taxa of Pogostemoninae senus. Bentham 1993 Subtribe Pogostemoni nae sensu Bentham (Labiatae) from South India 441

Figs. 1-12. Mitotic and meiotic chromosomes in Pogostemon. 1, P. auricularius n=17. 2, P. auricularius 2n=34. 3, P. benghalense n=32. 4, P. benghalense 2n=64. 5, P. gardneri n=16. 6. P. heyneanus n=32. 7, P. heyneanus 2n=64. 8, P. mollis n=16. 9, P. mollis 2n=32. 10, P. paniculatus n=16. 11, P. paniculatus 2n=32. 12, P. purpurascens n=17.

the 12 species so far cytologically known, seven are based on x=16 and three are known to have both x=16 and 17 while only two are based on x=17. This situation indicates that x=16 might be the primary basic number of the genus and that x=17 is derived by dysploidy from x= 16. It is of some cytotaxonomic interest that Hsu (1967) has reported n=6 in Dysophylla auricularia which is now transferred to Pogostemon as P. auricularius (El-Gazzar and Watson 1967, Cramer 1981, Rani and Mathew 1983, Bennet 1987). But other reports in this species (Chuang et al. 1963, Bir and Saggoo 1985, Present study) have shown either n=17 or 2n=34. Therefore Hsu's report of n=6 may not be considered as derogatory to the above hypothesis on the basic cytological situation in Pogostemon till at least n=6 is confirmed by a second 442 Mariamma Cherian and P. I. Kuriachan Cytologia 58

Figs. 13-21. Mitotic and meiotic chromosomes in Pogostemon, Eusteralis and Colebrookea. 13, P. purpurascens 2n=34. 14, P. wightii n=16. 15, P. wightii n=32. 16, P. wightii 2n=64. 17, E. stellata var. roxburghiana n=14. 18, E. tomentosa var. gracilis 2n=32. 19, E. tomentosa var. gracilis 2n=32. 20, C. oppositifolia n=16. 21, C. oppositifolia 2n=32.

observation. The chromosome numbers n=14 in Eusteralis stellata var. roxburghiana and n=16 in E. tomentosa var. gracilis (Present study) indicate that x=14 and 16 are the basic chromosome numbers of the genus. The only previous chromosome count on the genus is 2n=72 in E. stellata (Borgmann 1964). Obviously this is a polyploid number, but not a direct multiple of x=16 and therefore more critical cytological work is needed to reveal cytological evolution of this species. The present count of 2n=32 for the monotypic genus Colebrookea is in conformity with the previous reports of Gajapathy (1961) and Gill (1971). As n=16 is the only chromosome number known in the genus, it may be suggested that the genus is based on x=16. Owing to the lack of adequate cytological data on the assemblage, a cytotaxonomic approach to the problem of systematic position of Pogostemoninae has not been attempted so far. Comparative analyses of basic chromosome numbers and chromosome size in South Indian Labiatae (Cherian 1990) have shown that the subfamily Nepetoideae of Erdtman (1945) is characterised by predominantly 5-based chromosome numbers and comparatively large chro 1993 Subtribe Pogostemoninae sensu Bentham (Labiatae) from South India 443

mosomes (0.9-4.0ƒÊm) while subfamily is mostly 7-based and with small chromo somes (0.67-2ƒÊm). Cytology of Tetradenia in Pogostemoninae is not known . An examination of available cytological data on the other three genera shows that Eusteralis is based on x=14 and 16, Colebrookea on x=16 and Pogostemon on x=16 and 17 . The basic number x=14 is a direct multiple of the primary basic number x=7 , where as x=16 might have arisen from x= 7 by dysploidy followed by polyploidy . As has been shown above x=17 is derived by dysploidy from x=16. Besides all these genera have small chromosomes (0 .67-2ƒÊm). This reveals the close cytological affinity between the genera of Pogostemoninae and would render cytotaxo nomic support for the separation of the whole of Bentham's (1876) Pogostemoninae from the bulk of his Mentheae (subfamily Nepetoideae of Erdtman, 1945) and its inclusion in the subfamily Lamioideae of Wunderlich (1963).

Summary Cytology of 11 taxa in three genera belonging to the subtribe Pogostemoninae in Mentheae from South India is studied. The chromosome numbers observed were Pogostemon auricularius 2n=34, P. benghalense 2n=64, P. gardneri n=16, P. heyneanus 2n=34, P. wightii 2n=32 and 64, Eusteralis stellata var. roxburghiana n=14, E. tomentosa var. gracilis 2n=32, and Colebro okea oppositifolia 2n=32. The basic chromosome numbers suggested are x=16 and 17 in Pogostemon, x=14 and 16 in Eusteralis and x=16 for Colebrookea. On the basis of cytological data it is suggested that the whole of Pogostemoninae be included under the subfamily Lamioideae as done by Wunderlich rather than split it and divide the genera among Lamioideae and Nepetoideae as done by Erdtman.

Acknowledgement

One of the authors (MC) is grateful to the UGC for a Research Fellowship.

References

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