Cytologia 40: 285-299, 1975

Cytological Studies on Some Indian Members of

Bibha Bhattacharya

Cytogenetics Laboratory, Department of Botany , University of Calcutta, 35, Ballygunge Circular Road, Calcutta-19,

Received September 22, 1973

The family Commelinaceae forms a very natural assemblage, with mostly well defined genera under the present systems of classification. However the positions of these genera and their interrelationships still present controversial aspects. Earlier monographers like Clarke (1881), Bruckner (1930), Woodson (1942) and Rohweder (1956) have divided the genera into two major groups, based on either the stamen character or the , the Tradescantieae and the Commeli nieae. Clarke (l.c.) included a third tribe Pollieae as well. Pichon (1946) and Brenan (1966), however grouped the genera into ten and fifteen groups respectively, though on the basis of completely different characteristics. The cytological studies have helped in understanding the different complexes in , and the other common genera, though the data on , , , Streptolirion etc. have not given such a clear indication regarding their delimitations and positions. Different populations col lected from different habitats indicated differences in karyotype within members of the same species. Widespread polyploidy amongst the Indian members has also been recorded. The present work was undertaken on the members available in order to apply the cytological findings obtained i) to clarify the taxonomic controversies in the genera involved, ii) to indicate the lines of evolution within them if possible and iii) to observe the effects of factors like polyploidy and structural and numerical altera tions of chromosomes in speciation within them.

Materials and methods

Five genera of the family Commelinaceae including thirtyfive taxa have been selected for the present investigation. Most of the species under investigation were collected from different parts of West Bengal while a few have been obtained from regions in the Eastern Himalayas and Khasia Hills. Young healthy root tips were obtained from the sown in earthenware pots in a suitable mixture of sand and soil. The flowering in almost all of the plants mostly occurred from the months of September to November. Different populations of the same species collected from different areas have been designated as Types I, II, III, etc. They do not show any appreciable morphological differences excepting in two cases. For the somatic study different pretreating chemicals were tried. Paradich lorobenzene and 8-hydroxyquinoline were found to be the most suitable ones in 286 Bibha Bhattacharya Cytologia 40

different concentrations and mixtures at 10-12•Ž. After fixation in acetic acid

ethyl alcohol mixture (1:2), root tips were kept in 45% acetic acid for 10 minutes and were heated for 3-4 seconds in a mixture of 2% acetic-orcein solution and

N HCI (9:1). The materials were kept in the stain for 2-3 hours and squashed in 45% acetic acid. For meiotic study, anthers with suitable divisional stages from

Figs. 1-28a are somatic metaphase plates and idiograms of Zebrina pendula Types I and II, Cyanotis axillaris Type I, C. cristata Type I, C. fasciculata, C. vaga Types I and II , C. villosa, Murd annia nudiflora Types I and II, M. spirata, Commelina benghalensis Types I to VI, C. diffusa Types I to VI, C. paludosa Type I, C. paludosa var. viscida, C. salicifolia Types I and II , C. sikkimensis respectively. See details in Table 2. 1975 Cytological Studies on Some Indian Members of Commelinaceae 287 288 Bibha Bhattacharya Cytologia 40

fresh material and material fixed in acetic-alcohol (1:2), were smeared in 1% acetic-carmine solution. Figures were drawn at a table magnification of approximately •~2000 using a

Zeiss compensating eye-piece of •~12.5 with an aplanatic condenser' of 1.3 N. A. Chromosomes with secondary constrictions have been drawn in outline only.

Observations

The members of the family Commelinaceae so far studied show chromosome numbers ranging from as low as n=10 to as high as n=60. A critical analysis

shows that often different populations of the same species collected from different localities differ not only in chromosome number, but in different combinations of

the chromosomes as well as in finer morphological details. The chromosomes, in Table 1. Chromosome types observed

*1 Range in chromosome size for the different genera .

*1 Abbreviations used: m=median , sm=sub-median, st=sub-terminal, sa=satellited, s=secondary constriction.

Table 2. Karyotypes

Type I. Zebrina pendula Schnizl Cal, WB 24=2A+4B+4C+14E (Figs. 1 & la) Type II. Zebrina peudula Schnizl Shil 24=2A+2B+2C+2D+12E+4F (Figs. 2 & 2a) Type I. Cyanotis axillaris (L.) J.A. et J. H. Schultes (=Amischophacelus axillaris (L.) Rolla Rao et Kammathy) Bol, WB 20=4A+16C (Figs. 3 & 3a) Type I. Cyanotis crisiata (L.) D. Don. Garia, WB 24=2A1+2B+16C+4D (Figs. 4 & 4a) Table 2 (Contd.)

* Abbreviations used: Cal=Calcutta A , WB=West Bengal, Shil=Shillong, Meghalaya; Bol=Bolpur , Dar=Darjeeling, North Bengal; HG=Alipur Horticultural Garden , CU=University of Calcutta, FRI=Fodder Research Institute, Barr=Bar rackpore. 1975 Cytological Studies on Some Indian Members of Commelinaceae 291

Table 3. Meiotic behaviour of the chromosomes

* Irregularities observed in the above cases include early separation of chromosomes , late separation of chromosomes, laggard, univalent, unequal separation of chromosomes, grouping of chromosomes, interbivalent connections and chromatin matter in the form of droplets. Abbreviations used: presence +, absence -. 292 Bibha Bhattacharya Cytologia 40

general, are medium-sized. The largest chromosomes have been observed in Zebrina pendula, whereas very short chromosomes are noted in Murdannia nudflora. On the basis of their length, the chromosomes have been distinguished into long, comparatively long, medium, short and very short. Nuclei showing variant number and structure are found to be present in the same root tip in a few cases, when the number which occurs in highest frequency has been considered as the normal one. A wide variation in the karyotypes in the different genera of the family is noticed (Tables 1 and 2). In most of the cases meiosis has been found to be irregular (Table 3).

Discussion

Cytological observations in the classification of the family The family is a more or less natural one with mostly very well difined genera. The main problem at present is the classification of these genera. A glance at the earlier classifications shows that 'the Commelinaceae appears to have suffered un duly from a traditional impression that the family must somehow be divisible into two major groups-the Tradescantiae and the Commelinae' (Brenan l.c.). Tom linson (1966) collected the anatomical data on this family and tried to correlate them with the proposed classification of Brenan (l.c.). His observations emphasize the reticulate interrelationships between genera within the Commelinaceae and it is not surprising that major generic assemblages can not be clearly recognised. Cytologically the members of this family have formed ideal materials for the study of various aspects including different types of chromosome behaviour. Tra descantia and Rhoeo are perhaps the most thoroughly explored genera in this con nection. It will be attempted here to find out to what extent the present observa tions tally with the existing systems of classification, particularly that of Brenan (l.c.). In the group I of Brenan's system, Murdannia, Floscopa and Aneilema have been placed together with other genera not studied here. The close relationship between Aneilema and Murdannia is well known in as much as the latter was in cluded within the former till 1952. Most of the earlier chromosome number re ports attributed to Aneilema refer actually to species of Murdannia. Aneilema is a predominently Tropical African genus with range of chromosome numbers includ ing x=9, 10, 13, 15 and 16. Murdannia is much more wide spread with a prepon derance of species in and an usual basic chromosome set of x=10 in addition to 6 and 11. The distinctness of these two genera is shown by the differences in chromo some numbers and anatomical characters (Tomlinson I. c.) besides their floral mor phology. Their inclusion within the same group by Brenan (l.c.) can be supported on the basis of cytological evidences since inspite of differences in chromosome numbers their karyotypes show an overall similarity in their graded nature and medium to small size. The third genus Floscopa as seen here shows n=15 chromo somes. Other reports are x=12 in from India (Kammathy and Rao 1961) and x=12, 18 and 36 in different species collected from West (Morton 1967). The observed by the present author is possibly an aneuploid 1975 Cytological Studies on Some Indian Members of Commelinaceae 293 member. The predominance of x=12 and 18 in Floscopa fits in with the general pattern exhibited in the tribe Tradescanteae (x=6 or 12) as a whole in the systems of classification followed by Clarke (Lc.) and Woodson (l. c.). Bruckner (l.c.) has placed Floscopa with Commelina and Aneilema under the sub-family Commeli naceae in his system. The basic numbers observed in Floscopa however indicate that this genus should be more conveniently placed in the x=6 or 12 series followed by Tradescanteae. Thus the inclusion of Floscopa with Aneilema and Murdannia either in group I of Brenan or Commelinaceae of Bruckner can not be supported from cytological evidences. Within the group VI Brenan has included the genera Belosynapsis and Cyano tis. He has not justified the separation of the genus Zygomenes as done by Salis bury (1812) or its Amischophacelus as proposed by Rao and Kammathy (1966) from the genus Cyanotis. However the cytological data available show that the three genera Amischophacelus, Belosynapsis and Cyanotis are quite distinct with basic sets of x=10, x=13 and x=12 respectively occurring in the highest frequency. In fact the suggestion made by Sharma (1955) of the separation of the species Cya notic axillaris into a different genus on the basis of its chromosome number and advanced nature of karyotype was fully justified by the conversion of this species into Amischophacelus axillaris as done by Rao and Kammathy (l.c.) on morpho logical grounds. The inclusion of these three genera within the same group by Brenan can however be justified from a study of the karyotypes which show an overall gross similarity inspite of numerical and minor structural differences. The group X of Brenan includes the genus Commelina. In general this genus is a distinct one with several complexes. The most frequent basic number observed in the Indian species is x=15 excepting for a few cases like x=11 in C. benghalensis and x=14 in certain populations of C. diffusa. The homogeneity of this genus is also indicated by an overall similarity of the karyotype, being mostly graded from medium-sized to short and with constrictions ranging from sub-median to sub terminal in position. In the XII group of Brenan, the genus Zebrina has been placed in addition to others. The chromosomes of Zebrina as observed here and also previously are rather distinctive being long and having a basic number of x=6. The primary constrictions range from median to sub-terminal in position (Sharma l. c.). Taken in all, however, the cytological evidences so far available on this family indicate that there are two distinct chromosomal lines, one of them has a possible basic set of x=4 (Sharma l.c.) or x=5 (Lewis, W. H. 1964) with medium-sized to short acrocentric chromosomes. This line has given rise to the genera like Mur dannia, Aneilema, Commelina, etc. The other line with x=6 and mostly large metacentric chromosomes is responsible for the genera like , Zebrina, Setcreasea, etc. A third possible line is indicated by the basic number of x=16 (8?) as observed in Pollia. Therefore the cytological data possibly fit in more with the division of the Commelinaceous genera into two major groups represented by the Tradescantia and Commelina types. However, a rigid classification into two groups does not provide the correct status for intermediate genera like Cyanotis or Callisia or the other sublines arising through interbreeding of these two major lines. There 294 Bibha Bhattacharya Cytologia 40

fore the subdivision into ten or more groups as done by Pichon or Brenan, though artificial, forms a system more compatible with cytological data. However de tailed cytological studies of the members of the family from different areas of the world and also evidences from anatomy, embryology and palynology are necessary for supporting any classification based on morphological grounds alone. Cyto logical evidences as obtained here are as yet insufficient to more than just indicate affinities between the different genera already grouped according to morphological characteristics. Interrelationships within the genera studied i. Zebrina: The only member of the genus Zebrina studied, Z. pendula is cultivated as an ornamental plant in India. The two populations studied here collected from different altitudes show the same chromosome number 2n=24 as observed previously (Sharma l. c.). The chromosomes are distinctive being long to medium-sized and having a very long pair of metacentric chromosomes. The karyotype differs in structural details from those observed by Darlington (1929) and Sharma (l. c.). Darlington (l.c.) from a study of the chromosomes suggested the origin of this species through autopolyploidy from species of Tradescantia having n=6 chromosomes, a view supported by Sharma (l.c.) as well. The dis crepancies in the karyotypes of this species as observed by the present and previous authors may be accounted for on the basis of irregular chromosome behaviour giving rise to structural changes of chromosomes as observed during the meiotic as well as to some extent in the somatic behaviour of the species. Secondary as sociation of bivalents shows the formation of groups of bivalents 4, 5 and 6 in number. If the contention of Darlington of considering the maximum association as indicative of the basic number is accepted, the basic set for this species would appear to be x=4. The possible corollary that the x=6 set of the Tradescantieae line is a derived one is very controversial and no suggestions can be put forward unless many more evidences are available. ii. Amischophacelus and Cyanotis: These two genera together with Belo synapsis were previously included as three well defined sections of the genus Cyanotis D. Don. (s. l.). They were separated on morphological grounds by Sprague and Fischer (1928) and Salisbury (I.c.) and later by Rao and Kammathy (l.c.). Cyto logical data as mentioned before fully justify the allotment of a generic status to C. axillaris as Amischophacelus axillaris (Rao et a1. 1968, Sharma l.c.). The present observations also indicate that in the chromosome number (n=10) and in karyotype with predominantly sub-terminal constrictions A. axillaris differs significantly from the other species of Cyanotis studied. These three genera have been included on morphological grounds in most classifications within the group Tradescantieae. Therefore on the basis of chromosome morphology as observed here and previously resembling the Commelina line and the number indicative of the Tradescantia line, these three genera possibly indicate the relationships between these two lines. Tak ing these factors into account their inclusion as a distinct tribe Cyanoteae (Pichon l. c.) or group VI of Brenan (l.c.) separate from Tradescantieae or Commelinieae appears to be more justified. iii. Murdannia: The Indian species of Murdannia were originally included 1975 Cytological Studies on Some Indian Members of Commelinaceae 295 under Aneilema R. Br. In 1930 Bruckner revived the genus Murdannia and later most of the Asiatic species of Aneilema were transferred to Murdannia Royle, on the basis of flower, staminode and capsule characters. The distinctness of Murdannia from Aneilema is supported by cytological (Kammathy and Rao 1961, 1964) and anatomical studies (Tomlinson l.c.). Most of the species of Murdannia studied here or previously show n=10 or its multiple numbers, though other numbers like n=9, 11 and 12 are sometimes observed (Briggs 1966, Kammathy and Rao l.c., Lewis l.c., Mitra and Datta 1967, Morton 1966, Raghavan and Rao 1961, Rao et al. l.c., Shetty and Subramanyam 1962). According to Lewis (l.c.) the original basic number for Murdannia was x=5 which is present now as a dominant line of x=10. The other numbers like x=9, 11 and 12 are possibly derived ones from the basic x=5 and evolution has progressed in them along parallel lines. According to the classification adopted by Bruckner (l.c.), Murdannia has been included in the sub family Tradescantieae but Aneilema has been retained within the other sub-family Commelinieae in the same tribe as Commelina and Floscopa. This position of Murdannia in Tradescantieae can not be supported at all from the cytological evi dences as chromosome number (x=10) and karyotype. In this connection the inclusion of Murdannia and Aneilema together in a separate group I by Brenan (l. c.) is much more phylogenetic. iv. Floscopa: In the genus Floscopa the basic number as observed previously is x=12 though the numbers x=9 and 15 have been reported by Morton (l.c.) and in the present work. The inclusion of this genus in the tribe Tradescantieae by Clarke (l.c.) and Woodson (l. c.) fits in with the general pattern exhibited in this tribe (x=6 or 12 with long metacentric chromosomes). The other numbers x=15 and 18 may possibly be derived ones. Regarding this genus, its inclusion with Aneilema and Murdannia in the group I of Brenan (l. c.) can not be supported. The chromosomes of the genus Commelina also both in nubmer (mostly n=11 and 15) and structure (mainly small acrocentric) are not similar with those of Floscopa and therefore the inclusion of these two within the sub-family Commelinieae as done by Bruckner (l.c.) can not be justified. v. Commelina: This genus can be distinguished easily from the others in its foliaceous spathe but the delimitations of the different species are rather contro versial. The chromosomes are mainly of medium size with mostly sub-median primary constrictions. Most of the Indian species show n=15 or its multiples. C. benghalensis however shows a mostly uniform series of 2n=22 chromosomes both from previous and present records (Briggs l. c., Fukumoto 1965, Ganguly 1946, Kammathy and Rao l.c., Lewis l. c., Malik 1961, Panigrahi and Kammathy 1964, Shetty and Subramanyam l.c.). In this connection the contention of Lewis (l.c.) that for the group Commelinieae in general and the genus Commelina in particular x=5 may form the basic set from which other numbers like x=11, 14 and 15 may have arisen appears to be quite probable. Of the different systems of classifications the inclusion of this genus in a separate group X by Brenan appears to be the one most in accordance with the cytological data. Relative importance of different forms of polyploidy in the evolution of the species Polyploidy through which immediate genetical isolation can be attained in 296 Bibha Bhattacharya Cytologia 40 some cases, has occurred in many occasions in the Commelinaceae. Several of these intraspecific polyploids may be of autoploid origin like the occurrence of 2n=28 and 56 in Commelina diffusa and 2n=45, 60, 100 and 150 in Commelina paludosa (Sharma l. c. and Sharma and Sharma 1958). The absence of a large number of multivalents though possibly due to the short size of chromosomes may also result from structural alterations accompanying polyploidy. Though Sharma and Sharma (l.c.) tentatively suggested that autopolyploidy alone can not account for speciation yet Morton (l.c.) indicates a complete isolating effect of polyploidy in certain cases. In support he cites the occurrence of multivalents in diakinesis in hexaploid C. benghalensis observed by him. In other cases he regards the isolating effect of polyploidy to be not complete since intermediate forms are also found such as in Aneilema umbrosum. Allopolyploidy however has been a major factor in evolution at least in most of the Indian populations since in the high polyploid forms of some species regular meiosis and absence of multivalents together with high fertility of pollen grains have been observed. The most effective mode of speciation in this family has evidently been through aneuploidy particularly in the genera Murdannia, Aneilema, Commelina and Cya notis. The members of the genus Commelina show multiples of 11, 12, 14 and 15 chromosomes in different species as well as within the members of the same species. For example, populations of Commelina diffusa observed here show 2n=28, 30 and 60 chromosomes. In C. paludosa previous and present reports from this laboratory show numbers ranging from 2n=45, 60, 100, 120 to 150. Morton (I.c.) reports populations with 56, 58 and 60 in C. erecta and C. diffusa. These numbers indicate that so far as speciation in this family is concerned, allo and aneuploidy have played much more important roles than autoploidy. Polyploidy in relation to distribution Some cases of the distribution of polyploids and diploids in ecologically dif ferent habitats have been recorded in different members of this family, observed in this laboratory. For example diploid forms of Commelina diffusa (2n=28 and 30) have been found in the tropical plains while the polyploids (2n=56 and 60) occurred in different regions of the Eastern Himalayas. Anderson and Sax (1936) had re ported polyploid types of the same species from the tropics. Possibly, therefore, this species has originated in the tropics and produced polyploid types which due to their greater tolerance later migrated to the higher altitudes. Role of structural and numerical alterations in evolution The role of alterations in chromosome structure in speciation is well known. In the origin of different members of the family studied here, structural alterations have been as important as the changes in the number of chromosomes, in the evolu tion of new forms. Even within the members of different populations collected from different areas of the same species, changes in chromosome structure are observed to a greater or lesser extent. A major factor in the maintenance of structural and numerical alterations in different populations of this family is the fact that, most of the tropical members are propagated either partially or sometimes wholly through vegetative means. 1975 Cytological Studies on Some Indian Members of Commelinaceae 297

The entrance of a variant nucleus into the growing apex of an asexually reproducing plant may give rise to a new form leading to the formation under favourable cir cumstances of a new taxon. Basic numbers and lines of evolution It is apparent from the cytological studies on this family made earlier and here that there are two major lines of evolution, one involving long metacentric chromo somes and the other forming a line with medium-sized to short acrocentric ones. The basic number of the former has been suggested to be x=6 and of the latter as x=4 (Sharma l.c.) or x=5 (Lewis l. c.). These two lines representing the Trades cantieae and the Commelinieae complexes respectively have originated very early and have given rise to different sub-lines with derived basic numbers. The obser vation of maximum groupings ranging from 4, 5 to 6 groups of bivalents in Zebrina and Cyanotis made here suggest, if the concept of secondary associations of biva lents representing ancestral homology is taken to be correct, that the number x=6 for Tradescantieae may have been a derived one as well. Genera like Cyanotis which combine the basic number of Tradescantieae (n= 12) with chromosome structure of Commelinieae serve to exemplify the relation ships and the inter breeding between these two major lines which have resulted in the other sub-lines. Reviewing the different systems of classification, therefore, any complete divi sion of the genera into two or three groups is untenable from the point of view of their cytology since it does not accommodate the cytologically intermediate forms in their proper positions. The classification followed by Pichon (l.c.) or Brenan (l.c.) is more compatible with the cytological data since they group the taxa together as climaxes of different sub-lines of evolution. The chromosome studies lend a greater support to the latter systems of calssification.

Summary

Thirtyfive taxa under five genera of the family Commelinaceae have been studied cytologically. Different populations of the same species collected from different regions of Eastern India have also been studied. The chromosome num bers determined range from 2n=20 to 120. The chromosome complements of different populations of the same species have been found to differ from each other not only in the number but also in the structure of the chromosomes to a greater or lesser extent. In the origin of different members of the family studied here, structural alterations have been as important as the changes in the number of chromosomes, in the evolution of new forms. In speciation in this family as seen from chromosome number records allo and aneu ploidy have played much more important roles than autopolyploidy. Variations in the chromosome complements in somatic nuclei of the same individual have been found in some cases. Since all the species are propagated profusely through vegetative means, the occurrence of varying numbers in the somatic tissue obviously provides scope for the origin of new types; through their entrance into the growing apex of daughter shoots. 298 Bibha Bhattacharya Cytologia 40

In view if the data obtained so far, it has been suggested that there are two major chromosomal lines within the family Commelinaceae, one starting from a basic set of 4 or 5 comparatively short chromosomes, the other from a basic set of 6 long chromosomes. The other numbers are apparently derived ones. Reviewing the different systems of classification, the one followed by Pichon (1946) or Brenan (1966) has been found to be more compatible with the cytological data since they group the taxa together as climaxes of different sub-lines of evolu tion. Cytological evidences are more in favour of them rather than of the systems recognising only two major groups within this family.

Acknowledgement

The author wishes to express her sincere gratitude to Dr. Archana Sharma for guidance and to Prof. A. K. Sharma, Head of the Department of Botany, Univer sity of Calcutta, for facilities provided.

References

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