Cytologia 43: 289-303, 1978

Cytological Studies on South Indian

K. Ramachandran Departmentof Botany,University of Kerala,Trivandrum, India ReceivedSeptember 21, 1976

Araceae is a large family consisting of 1400-1500 in 105 genera (Lawrence 1960), distributed largely in the tropics. The family includes three important tuber crops, viz. dasheen or taro (Colocasia esculenta Schott), tanier (Xanthosoma sagitti folium Schott) and elephantfoot yam (Amorphophallus campanulatus B1.) widely cultivated in most tropical countries. Other cultivated species of less importance are Alocasia indica and Typhonium trilobatum. The aim of the present investigation has been chromosome studies of cultivated and wild tuberous species of the Araceae. Cytological observations on 30 species, mostly indigenous to South India are pre sented in this paper. Karyological studies of four South Indian species of Amor phophallus have been reported elsewhere (Ramachandran 1977).

Materials and methods

All the materials investigated in the present study except Theriophonum minutum,

Typhonium trilobatum and Arisaema wightii, were collected from different localities in Kerala, South India. Acetocarmine squashes of root tips and anthers fixed in 1:3 acetic alcohol were made according to the usual method. Root tips of with large or medium sized chromosomes were treated with 0.002M aqueous solution of 8-hydroxy

quinoline at about 4•Ž for 3-4 hrs. and of plants with small chromosomes chilled for an hour in water at 4•Ž prior to fixation. For meiotic studies, parts of spadices with staminate flowers or stamens were directly fixed in acetic alcohol. The chromosome numbers of taxa determined in the present study are listed in Table 1. The tribes and genera have been arranged following Hutchinson's

(1934) system of classification. The species have been arranged alphabetically. Classification of chromosomes as short (below 3ƒÊ), medium (3-6ƒÊ) and large

(over 6ƒÊ) has been adopted from Delay (1951).

Observations

Acorns calamus Linn. (Sweet flag). This is a polymorphic species, wide-spread in the North temperate region, tropical Asia and Eastern North America. Materials

examined in the present study were collected from shallow canals near Veli Lake, west of Trivandrum city. Root tip cells showed 45 chromosomes, which range between 0.75ƒÊ and 2.1ƒÊ

in length (Fig. 1).

Lasia spinosa Thw. It has a diploid chromosome number of 26 (Fig. 2). Chromo- 290 K. Ramachandran Cytologia 43

Table 1. Chromosome numbers in the Araceae

comes vary from 1.6 to 2.7ƒÊ in length.

Anaphyllum wightii Schott. The somatic complement consists of 26 chromosomes, which range between 1.8 and 5ƒÊ in length. A pair of chromosomes bear satellites 1978 Cytological Studies on South Indian Araceae 291

at the ends of long, thin connecting strands (Fig. 3).

Meiosis is regular. Thirteen bivalents have been observed at first metaphase

(Fig. 4). Pollen is 98% normal and the shows good seed setting.

Dieffenbachia pieta Schott. Dieffenbachia is a tropical American . D. picta is found in shallow ditches in many localities in Trivandrum, and is evidently an escape from gardens. Materials of this species showed 2n=34 chromosomes (Fig. 5). They are large, between 4.0 and 10.7ƒÊ in length. Meiosis is regular. Seventeen bivalents have been found in PMCs at first metaphase (Fig. 6). However, no seed setting has been found in these plants.

Steudnera discolor hort. This garden plant has a somatic complement of 56 chromo somes (Fig. 7). They range between 1.2 and 2.7ƒÊ in length, and most of them have median centromeres.

Remusatia vivipara Schott. This species occurs at higher elevations in South India.

Plants of this species showed a 2n chromosome number of 28. In length they range between 2.1ƒÊ and 3.3ƒÊ. Twelve pairs have median and the others submedian centromeres (Fig. 8).

Colocasia antiquorum Schott. The tender leaves of this species are used as a vegeta ble. A few varieties differing chiefly in height of plant, pigmentation of petioles and veins, leaf blade and margin have been recognized. Cytological observations on two varieties, a diploid and a triploid are given below.

C. antiquorum (diploid). This variety is characterised by green petiole and blade and light purple spot on the upper surface of leaf blade at the point of insertion of the petiole. Root tip cells of this variety showed 28 chromosomes, 2.5-4.8ƒÊ in length. Centromeres are median in six pairs and submedian in the others (Fig. 9). Meiosis is regular except for occasional lagging chromosomes at first anaphase. Fourteen bivalents are regularly found at first metaphase (Fig. 10). The pollen is 90% stainable with acetocarmine.

C. antiquorum (triploid). This variety has dark purple petioles and veins and dark green leaf blades with purple margins. The somatic complement consists of 42 chromosomes. They are smaller

(1.7-3.8ƒÊ) than those of the diploid (Fig. 11).

C. esculenta Schott. Popularly known as taro or dasheen, this is an important tuber crop, extensively cultivated in many tropical and subtropical countries. Over 1000 horticultural varieties are grown in different parts of the world (Greenwell 1947). Seventeen varieties were assembled during the present study, which include 3 from

Assam, 2 from Andhra Pradesh and one from Nepal, the other 11 being from Kerala State. Seven of these varieties (6 from Kerala and 1 from Nepal) were diploids (2n=28) and the others triploids (2n=42). Cytological observations on 292 K. Ramachandran Cytologia 43 1978 Cytological Studies on South Indian Araceae 293

two South Indian varieties, a diploid and a triploid are given below.

C. esculenta (diploid). "Chutti". This is a medium sized plant, growing up to one metre in height. Leaves are green except for a pink spot on the upper surface of the blade at the point of insertion of the petiole. Fig. 12 shows the somatic chromosomes (2n=28) of this variety. Chromo somes vary in length between 2.1ƒÊ and 4.8ƒÊ. Centromeres are median in five pairs and submedian in the others. Meiosis is largely regular. Fourteen bivalents are found at first metaphase

(Fig. 13). The mean number of xta per bivalent, averaged from 20 metaphase I plates is 1.7. Precocious separation of dyads at metaphase I and laggards at anaphase I are observed in a small proportion of cells. The pollen is 95% well formed (Fig. 14) and their fertility was confirmed by germination tests in 100ppm aqueous solution of boric acid.

C. esculenta (triploid). "Kari Chembu". The plant grows to over 1.2 metres in height. Petioles and veins are purple. The somatic chromosome number of this variety is 42. They range in length between 2.1ƒÊ and 4.3ƒÊ (Fig. 15). PMCs show varying numbers of trivalents, bivalents and univalents at first metaphase (Fig. 16). The number of univalents ranges between 2 and 8. Analysis of 17PMCs showed a mean of 4.3 univalents per cell. Chromosomes lag at ana phases of both divisions. The pollen shows a wide range in size, About 33 are well-filled (Fig. 17).

Sterility in Colocasia: Both C. antiquorum and C. esculenta are propagated ex clusively by vegetative means and sexual reproduction is not known. The sterility in C. antiquorum was investigated by Mayeda (1932) and Banerji (1934, 1937). Mayeda found certain irregularities in microsporogenesis to which he attributed the apparent sterility. Banerji confirmed Mayeda's findings. However, in the diploid varieties of both species of Colocasia investigated in the present study, the course of meiosis was regular and pollen fertility, as determined by staining and germination tests, was also high. The development of fruits and seeds also appeared normal. The embryos, though small, were well-formed. However, the seeds fail to germinate under natural conditions. It was shown that the embryos can be grown in culture medium (Abraham and Ramachandran 1960). This work has opened up possibilities of breeding in this crop so far considered impossible.

Figs. 1-17. All figs, except 14 and 17, •~1000. Figs. 14 and 17 •~320. 1, Acorus calamus, 2n=45. 2, Lasia spinosa, 2n=26. 3, Anaphyllum wightii, 2n=26. 4, prometaphase in a PMC of A. wightii showing 13 bivalents. 5. Dieffenbachia pieta, 2n=34. 6, metaphase I in a PMC of D. pieta showing 17 bivalents. 7, Steudnera discolor, 2n=56. 8, vivipara, 2n=28. 9, Colocasia antiquorum, 2n=28 (diploid). 10, metaphase I in a PMC of diploid C. antiquorum showing 14 bivalents. 11, C. antiquorum, 2n=42 (triploid). 12, C. esculenta, 2n=28 (diploid). 13, meta phase I in a PMC of diploid C. esculenta showing 14 bivalents. 14, pollen of diploid C. esculenta. 15, C. esculenta, 2n=42 (triploid). 16, metaphase I in a PMC of triploid C. esculenta showing trivalents, bivalents and univalents. 17, pollen of triploid C. esculenta showing the large proportion of sterile pollen. 294 K. Ramachandran Cytologia 43 1978 Cytological Studies on South Indian Araceae 295

Alocasia fornicata Schott. Materials of this species showed 2n-42 chromosomes

(Fig. 18). In length, they vary between 2.6ƒÊ and 6ƒÊ.

Alocasia indica Schott. This species is cultivated in South India. Its starchy root stock grows to large dimensions, up to 2.5 metres in height and a diameter of 30cm. It has a diploid chromosome number of 28 (Fig. 19). The chromosomes measure 3.6ƒÊ to 5.9ƒÊ in length. Ten pairs have median and the others submedian centromeres.

Alocasia montana Schott. Root tip cells showed 28 chromosomes (Fig. 20). Their length ranges between 3.3ƒÊ and 5.5ƒÊ. Centromeres are median in all the chromo somes.

Caladium bicolor Vent. Caladium is a tropical American genus. C. bicolor is one of the two species of Caladium commonly grown in gardens. It is now commonly met with in many localities, occupying waste lands and is an escape from gardens. There are 30 chromosomes in root tip cells (Fig. 21). The karyotype is distinctly asymmetrical. in regard to length of chromosomes, the largest pair being 6.5ƒÊ and the shortest 1.9ƒÊ. All the chromosomes except one pair show median centromeres. Five pairs have secondary constrictions. Fifteen bivalents have been observed at first metaphase (Fig. 22), Twelve per cent of the PMCs (6 out of 50 examined) showed a single chromatid bridge and an acentric fragment at anaphase I, as in Fig. 23. The uniform length of the acentric fragments indicates that the plant is heterozygous for paracentric inversion. The pollen is 90% well formed. However, no seed setting is found, which may be due to self-incompatibility.

Xanthosoma sagittifolium Schott. Popularly known as tanier, this is a native of South America. This is now extensively cultivated throughout the West Coast of South India for its edible tubers which resemble those of taro, but are larger. The somatic chromosome number of this species is 26 (Fig. 24). Chromosome length ranges between 2.7ƒÊ and 6.0ƒÊ. Six pairs have median, and the others submedian centromeres. A pair of chromosomes bear satellites.

X. violaceum Schott. This species is also cultivated for its tubers and for its foliage which is used as a vegetable. It is also grown in gardens for its purplish-veined leaves.

This species also has 2n=26 chromosomes (Fig. 25). They are smaller than those of X. sagittifolium, being 1.7ƒÊ to 4.3ƒÊ in length. Centromeres are median in six pairs and submedian in the others.

Figs. 18-32, •~1000. 18, Alocasia fornicata, 2n=42. 19, A. indica, 2n=28. 20, A. montana,

2n=28. 21, Caladium bicolor, 2n=30. 22, metaphase I in a PMC of C. bicolor showing 15 bivalents. 23, anaphase I in a PMC of C. bicolor showing a single chromatid bridge and an acentric fragment. 24, Xanthosoina sagittifolium, 2n=26. 25, X. violaceum, 2n=26. 26, Ariopsis peltata, 2n=28. 27, Pistia stratiotes, 2n=28. 28, Theriophonum indicum, 2n=16. 29, metaphase I in a PMC of T. indicum showing 8 bivalents. 30, T. infaustum, 2n=16. 31, T. minutum, 2n=16. 32, metaphase I in a PMC of T. minutum showing 8 bivalents. 296 K. Ramachandran Cytologia 43

Figs. 33-50. •~1000. 33, Typhonium cuspidatum, 2n=16. 34, metaphase I in a PMC of T. cuspidatum showing 8 bivalents. 35, T. trilobatum, 2n=36. 36, T. bulbiferum, 2n=20. 37, 1978 Cytological Studies on South Indian Araceae 297

Pistia stratiotes Linn. This is a common floating water plant of the tropics and subtropics. It has a somatic complement of 28 chromosomes, 0.5-1.5ƒÊ in length

(Fig. 27).

Theriophonum indicum Engl. A diploid chromosome number of 16 has been found in this species. The chromosomes range in length between 4.8ƒÊ and 8.0ƒÊ, and all have median centromeres (Fig. 28).

Meiosis is normal and eight bivalents are observed at first metaphase (Fig. 30). There is good pollen and seed fertility.

T. infaustum N. E. Br. Materials of this species collected from Palghat, central Kerala, also showed a diploid chromosome number of 16. They vary between 4.6ƒÊ and 6.5ƒÊ in length and all have median centromeres (Fig. 29).

T. minutum Engl. Materials of this species were obtained from Annamalainagar, Madras State. This is the only species of this genus that has been previously studied cytologically. Asana and Sutaria (1939) reported 2n=16, and the present study agrees with their observation. The chromosomes range in length between 5.3ƒÊ and 8.5ƒÊ. Centromeres are median in three pairs, submedian in four and subtermi nal in one (Fig. 31). Meiosis is regular. Eight bivalents are consistently observed at first metaphase

(Fig. 32). The pollen is 97% normal.

Typhonium cuspidatum Dcne. This species showed 16 somatic chromosomes

(Fig. 33). They range in length between 3.7ƒÊ and 5.9ƒÊ. Centromeres are sub median in two pairs and subterminal in others. Meiosis is regular and eight rod-shaped bivalents were found at first metaphase

(Fig. 34).

T. trilobatum Schott. Thirty six chromosomes, 2.1-3.8ƒÊ in length, were found in root tip cells (Fig. 35).

T. bulbiferum Dalz. This species was collected from Konni forests in central Kerala by Prof. A. Abraham. It has not previously been reported from South India.

A diploid chromosome number of 20 is found in this species (Fig. 36). The chromosomes range between 1.6ƒÊ and 3.5ƒÊ in length. Centromeres are median in seven pairs and submedian in the others. Meiosis is regular. Metaphase I shows ten bivalents (Fig. 37).

T. divaricatum Dcne. The present study has revealed the existence of two chromo- diakinesis in a PMC of T. bulbiferum showing 10 bivalents. 38, T. divaricatum, 2n=52 (tetraploid). 39, diakinesis in a PMC of tetraploid T. divaricatum showing ring quadrivalents and bivalents. 40, T. divaricatum, 2n=65 (pentaploid). 41, diakinesis in a PMC of pentaploid T. divaricatum showing chains of five, rings of four, bivalents and univalents. 42, Arisaema leschenaultii, 2n=28. 43, A. neglectum, 2n=28. 44, A. wightii (male) 2n=28. 45, A. wightii (female) 2n=28. 46, A. tortuosum, 2n=56, 47, Lagenandra meeboldii, 2n=36. 48, L. ovata, 2n=36. 49, diakinesis in a PMC of L. ovata showing 18 bivalents. 50, Cryptocorype spiralis, 2n=112. 298 K. Ramachandran Cytologia 43

somal races of this species in South India, a tetraploid (2n=52) and a pentaploid

(2n=65). The tetraploid has cordate sagittate leaves, with rounded lobes, while the pentaploid is characterised by hastate deeply lobed leaves. In the pentaploid, the spathes are also broader. The somatic chromosomes of the tetraploid are shown in Fig. 38. They range

between 1.6ƒÊ and 2.9ƒÊ in length. Fig. 39 shows a PMC at diakinesis in the tetraploid. The PMCs show 6-9

quadrivalents in rings and chains, the remaining chromosomes being paired as bivalents. The distribution of chromosomes at first anaphase is regular (26:26) in most of the cells examined. Twenty six chromosomes are clearly observed in several metaphase II groups. The second division is also normal and the plant

forms normal tetrads of microspores in most cases. The pollen is 90% well filled and stainable in acetocarmine. The somatic chromosomes of the pentaploid of T. divaricatum are shorter than those of the tetraploid, ranging between 1.3ƒÊ and 2.3ƒÊ in length (Fig. 40). Chromosome associations in rings and chains are found at diakinesis in the

pentaploid race also (Fig. 41). Chains made up of five chromosomes have been observed. Rings consist of only four chromosomes. A variable number of univalents, bivalents and trivalents is also present. Anaphase separation is irregular due to the presence of the odd set of chromosomes. The pollen is, however, 86 stainable and shows variation in size.

Arisaema leschenaultii Schott. This species showed a somatic chromosome number of 28 (Fig. 42). The chromosomes vary in length between 2.7ƒÊ and 5ƒÊ.

A. neglectum Schott. The somatic complement in this species consists of 28 chromo somes (Fig. 43). They range between 2.7ƒÊ and 5ƒÊ in length.

A. wightii Bl. This is a dioecious species and both male and female plants were examined cytologically. The plants were collected from Kannikketti in Madras

State. The somatic chromosomes of the male and female plants are shown in Figs. 44 and 45 respectively. The chromosome number is 2n=28 in both. They show no obvious difference in size or shape of chromosomes.

A. tortuosum Schott. This is another dioecious species. Male plants of this species have been collected. They showed 56 chromosomes in root tip cells (Fig. 46). The chromosomes are smaller than those of the diploid species and range in length between 1.9ƒÊ and 3.0ƒÊ.

Lagenandra meeboldii Fischer. This species has 2n=36 chromosomes (Fig. 47). They vary from 1.0ƒÊ to 2.0ƒÊ in length.

L. ovata Thw. The somatic complement in this species also shows 36 small chromo somes, ranging in length between 1.3ƒÊ and 2.1ƒÊ (Fig. 48). Meiosis is regular and 18 bivalents have been observed at first meiotic division 1978 Cytological Studies on South Indian Araceae 299

(Fig. 49). The pollen is 94% normal. The plant shows good seed setting.

Cryptocoryne spiralis Fischer. The somatic chromosome number of this species

is 2n=112. The chromosomes are short , ranging in length between 1.0ƒÊ and 2.0ƒÊ (Fig. 50).

Discussion

The chromosome numbers of 30 species belonging to 17 genera determined

in the present study are listed in Table 1. They range from 2n=16 to 2n=112. Chromosomal variation and evolution in the family is discussed below. Previous reports of chromosome numbers in Acorus calamus indicate 9, 11 and 12

as basic numbers (Darlington and Wylie 1955, Love and Love 1961). The clone of A. calamus examined in the present study (2n=45) is possibly a pentaploid on the basic number 9. Tetraploid and hexaploid races based on 9 have been reported from northern India (Jammu and Kashmir) by Janaki Animal et al. (1964).

Lasia and Anaphyllum have been included in the tribe Lasieae by Hutchinson. Both genera have the same basic number, x=13, which indicates descent from a common ancestor. On the other hand, the karyotypes of the two genera Dieffen

bachia and Steudnera included in tribe Dieffenbachieae by Hutchinson indicate little relationship. D. picta shows a basic number of 17. S. discolor (2n=56) is

possibly a tetraploid on the basic number 14. Chromosomes are large in Dieffen bachia and short in Steudnera. In some morphological and anatomical characters Steudnera shows affinities to members of tribe Colocasieae, and Engler has included

the genus in subfamily Colocasioideae. Basic number 14 and the small size of chromosomes in Steudnera suggest closer kinship to members of tribe Colocasieae. Cytological data suggest that the tribe Dieffenbachieae needs revision.

In four of the six genera of Colocasieae investigated in the present study (Remu satia, Colocasia, Alocasia and Ariopsis) the basic number is 14. In Caladium, the variety of C. bicolor examined in the present study showed n=15, as in most varieties studied previously. However, Sharma and Das (1954) reported 2n=28 in three varieties. Somatic chromosome number of 28 was also observed by Jones

(1957) in C. chanjus. It appears, therefore, that in Caladium also x=14 may be the original basic number, and that in some varieties of C. bicolor there has been

aneuploid increase by gain of a pair of chromosomes. In Xanthosoma, on the other hand, the basic number 13 indicates the opposite tendency of reduction in chromo some number.

The monotypic genus Pistia has been assigned to a separate tribe Pistieae by Hutchinson and to a separate subfamily Pistioideae by Engler. Pistia stratiotes shows a basic number of 14, as in many other genera of the Araceae, but the chromo somes are the smallest (0.5ƒÊ-1.5ƒÊ) observed so far in any aroid.

The five genera, Theriophonum, Typhonium, Arisaema, Lagenandra and Crypto coryne are included in tribe Areae by Hutchinson. In all three species of Therio phonum investigated in the present study the chromosome number is n=8 and 2n=16, the lowest so far known in the family. All the species show unspecialized karyotypes. 300 K. Ramachandran Cytologia 43

On the other hand, the four species of Typhonium investigated in the present study differ in number and external morphology of their chromosomes. Each species is characterized by a different basic number, viz., x=8, 9, 10 and 13. Of these, x=13 is also known in three other species investigated previously. Sharma and Mukho padhyay (1965) reported n=13 and 2n=26 in T. inapinatum, and Jones (1957) observed 2n=26 in T. diversifolium and T. giganteum. The basic number 13 pre dominates in the genus (in four out of seven species so far studied). However, this does not appear to be the original basic number of the genus. Eventhough n=8 is found in only a single species, the fact that all three species of the neighbouring genus Theriophonum, which is considered less advanced than Typhonium in respect of floral characters, have n=8 indicates that x=8 is probably the original basic number in the latter genus also. It is probable that in Typhonium there had been a progressive aneuploid increase in basic number from 8 to 9, 10 and 13. Banerji (1947) observed n=9 and 2n-18 in T. trilobatum from Bengal. Simmonds (1954) reported a 2n number of 26 for this species from Trinidad. Sharma and Mukhopadhyay (1965) confirmed n=9 and 2n=18 in plants from Bengal and suggested that the plants studied by Simmonds might have been wrongly identified. Plants of this species examined in the present study showed 2n-36 and are tetra ploids on the basic number 9. In 30 out of 40 species of Arisaema in which chromosome numbers have been determined previously, the basic number is 14 (Fedorov 1969). Two of the three South Indian species examined in this study are diploids (2n=28) and the other a tetraploid (2n=56) on this basic number. The two species of Lagenandra showed 2n=36, and one species in which meiosis was studied revealed 18 bivalents (present study). The basic number 18 is probably derived from x=9 by doubling. spiralis (2n=112) is an octoploid on the basic number 14. (A 2n chromosome number of 28 has been reported in C. ciliata (Tjio 1948)). This is the highest chromosome number found in South Indian aroids. The plant is a halophyte, found in marshes subject to frequent changes in salinity. The Araceae shows a wide range of basic numbers from 8 to 22. The com monest basic number in the family is x=14. Eventhough the haploid number 7 has not so far been found in any aroid, x=7 is assumed to be the original basic number of the family and that x=14 is derived by polyploidy (Mookerjea 1955, Jones 1957). The presence of chromosome number as low as n=8 in Theriophonum and Typhonium supports this view. Evolution of an aneuploid series (x=6, 7, 8, 9 and 10) from the original number x=7, followed by polyploidy might well have given rise to the wide range of basic numbers now observed in the family. The formation of an aneuploid series prior to polyploidy is indicated by the tribe Areae in which the low basic numbers x=8, 9 and 10 still occur in some genera. Basic numbers 13, 15 and 17 may have arisen by dibasic amphidiploidy, by combination of 6 and 7, 7 and 8 and 8 and 9 respectively or by gain or loss of chromosomes following polyploidy. Besides the numerical changes discussed above, the karyotypes in the Araceae also indicate variations in chromosome size and nuclear DNA content in evolution. 1978 Cytological Studies on South Indian Araceae 301

Small chromosomes (below 3ƒÊ) are characteristic of Acorus, Steudnera, Pistia, Lagenandra and Cryptocoryne. Large chromosomes (over 6ƒÊ) are found in Dieffen bachia. The other genera investigated in the present study have mostly chromosomes of medium size (3-6ƒÊ). In a few genera having the same chromosome number, variations in chromosome size indicate loss and gain of nuclear DNA in evolution. Remusatia, Colocasia, Alocasia, Ariopsis, Pistia and Arisaema have the same chromo some number (2n=28) but show differences in absolute size. There is, however, no definite trend of either phylogenetic increase or decrease in chromosome size. The most primitive genus Acorus has short chromosomes. So have the highly specialized genera Pistia, Lagenandra and Cryptocoryne. One thing common to these four genera is that they all thrive in aquatic or semiaquatic habitats. Reduc tion in chromosome size may be an adaptation to this ecological condition in these aroids. Variations in chromosome size and nuclear DNA content in higher plants and animals have been shown to be of adaptive significance (Stebbins 1966, Rees and Jones 1972).

Summary Cytology of 30 species (including several varieties) coming under 17 genera of the Araceae, mostly from South India has been studied. Chromosome numbers determined in the present study range from 2n=16 to 2n=112. Meiotic studies of 11 species and some varieties have been made. Caladium bicolor showed chromatid bridges and fragments at anaphase I. The tetraploid race of Typhoniumdivaricatum formed six to nine rings of four chromosomes at diakinesis. Pentaploid race of this species showed chains of five chromosomes and rings of four. Meiosis was largely regular in the other species studied. Aberrations in micro sporogenesis reported previously in diploid Colocasia antiquorum have not been found in plants of this species examined in the present study. Diploids of C. antiquorum and C. esculenta showed regular meiosis and seed formation. The embryos which abort under natural conditions have been grown in culture medium. Chromosome numbers determined in the present study and those reported previously in the family reveal the presence of a continuous series of basic numbers between x=8 and x=18. However, 22 out of 50 genera known cytologically so far have chromosome numbers in multiples of 14. In view of the low haploid numbers n=8 observed in two genera, x=14 is presumed to have been derived from the lower x=7 by doubling. The number 7 is suggested as the ancestral basic number of the family. It appears that aneuploid changes of chromosome numbers produced basic numbers of x=6, 7, 8, 9 and 10 in the early evolution of the family, after which polyploidy and dibasic amphidiploidy gave rise to the higher basic numbers (x=12 to 18) now found in the family. Karyotypes in the family also show differences in absolute chromosome size indicating changes in nuclear DNA in evolution. No definite trend of either phylo genetic increase or decrease of chromosome size is indicated by the available data. Reduction in size of chromosomes appears to have been an adaptation to an aquatic habitat in some genera. 302 K. Ramachandran Cytologia 43

Acknowledgements

The author is thankful to Prof. A. Abraham, formerly Head of the Department of Botany, Kerala University and now with the FAO, for guidance and suggestions. He is also indebted to Prof. C. A. Ninan, Head of the Department of Botany, Kerala University for critical reading of the manuscript. The assistance rendered by Mr. A. Krishnan Kutty Nair, Artist-Photographer in the Botany Department in the preparation of photographs is greatly appreciated. Financial assistance from the Indian Council of Agricultural Research is gratefully acknowledged.

References

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