1960 195
Cytotaxonornic Studies on Vigna
Nirad K. Sen and J. G. Bhowal AppliedBotany Section, Indian Institute of Technology,Kharagpur, India ReceivedJuly 28, 1959 Introduction The genus Vigna belongs to the tribe Phaseoleaeof the Fam. Legumi nosae. It is very closely related to Phaseolus L. and Dolichos L. two other genera of the tribe and is distinguishedfrom Phaseolus in having a slightly curved keel instead of a twisted or spirally coiled keel, and from Dolichos by its lateral stigma instead of a terminal one. The species which are widely cultivated throughout the world are V. sinensis (L) Savi, V. catjang, (Burm.) Walp. and V. sesquipedalis(L) Fruw. popularly known as cowpea, catjang bean and asparagus bean. They are grown as fodder, vegetable, pulse and green manuring crops. Among the other species Vigna oligosperma (=V. hosei Baker), is cultivated as cover and green manuring crop; V. vexillata (L) Benth. as a root crop, V. nilotica Delile: and V. capensis Walp, Hiern are also cultivated. The commonly cultivated cowpea, catjang bean and asparagusbean were distinguishedas three distinct species by Piper (1912), though he recognised that they were connected through intermediate forms and could be easily hybridized. According to Mackie (1946) V. sinensis, V. cylindrica (=V. catjang) and V. sesquipedalis should be includedin a singlespecies because they cross readily with one another, each group being given the rank of subspecies. The chromosome numbers of different speciesreported from time to time as given by Darlington and Wylie (1945) are given below:
In addition to these, chromosome number of V. vexillata has been re ported by Tschechow et. al. (1932) as 2n=22. 13* 196 N. K. Sen and J. G. Bhowal Cytologia 25
As controversy exists about the taxonomic relationship and reported chromosome number in the three commonly cultivated species of Vigna this cytotaxonomic study was undertaken. Inter-crossibility of the three species was also studied and is being. presented separately with genetical data. Sub. sequently cytotoxonomic and inter-crossibility studies were extended to the wild species so far, as they, could be collected, and those data are presented in this paper.
Materials and methods The eleven wild species of Vigna and two varieties each of the three cultivated species used in the present investigation were obtained as seed samples from different sources mentioned against their name in Table 1.
Table 1. Sources of seed stocks
To confirm the identity of these species, description of their morphology were compared with those given in different floras, specially Oliver's (1871) Flora of tropical Africa and Bentham and Mueller's (1864) Flora of Aus traliensis. As the Trans. S. Africa Phil, Soc XVI 382 (1906) and Man. Fl. Pl. Ferns Transval Pt. II PXXXV 420 (1932) were not available, wherein V. davii Bolus, and V. wilmsii Burtt. Davy. have been described their identification as given from the source had to be accepted. It has also been possible to compare herbarium sheets of V. vexillata (L.) Benth., V. luteola Benth. and V. marina (Burm.) Merr. with those kept in the herbarium of the Indian Botanical Garden, Calcutta. Cytological technique. Somatic chromosomes were studied in root tip 1960 Cytotaxonomic Studies on Vigna 197
squash. Root tips were treated in saturated solution of 8-hydroxy-quinolin or
Para-dichlorobenzene for about 1-11 hour at 12-14•Ž, washed in water, warmed just to boil in a mixture of 9 part 2% aceto-orcein pressing the material gently for spreading. To have a good spread the slide was alter nately warmed and pressed 2-3 times. 8-hydroxy-quinolin gave better pre parations with the wild species and para-dichlorobenzene with the cultivated ones. Camera lucida drawings were made at a magnification of •~2125.
Hybridization technique. In the three cultivated species, V. catjang,
V. sinensis and V. sesquipedalis, and in the three wild species, V. vexillata,
V. davyi and V. gracilis, flowers opened early in the morning between 5 and 6 A. M. and closed next morning. In V. parviflora, V. wilrsii and
V. oblongifolia flowers opened at noon and closed in the same afternoon.
Though the flowers of different species opened at different times, anthesis in all of them was found to be complete before 6 A. M. and probably it oc curred at night. In the cultivated species V. sinensis, V. sesquipedalis and
V. catjang, anthesis was found to start in the previous evening at about
8 P. M.
Emasculation in the afternoon between 3-5 P. M. and pollination in the next morning between 6-8 A. M. proved most successful. Generally, one flower from an infloresence was emasculated and the all others were removed.
The emasculated flowers opened next day at about the usual time and were pollinated directly from the flower of the other parent. After pollination the flowers were bagged again.
Observations
Except in V. vexillata and V. davyi, flowers, fruits and seeds in all the other wild species are comparatively smaller than the cultivated ones.
Their stems are narrow and the twining habit more prominant. Easily dis tinguishable characters of the species have been given in Table 2.
Table 2. Distinguishing characters of the species 198 N. K. Sen and J. G. Bhowal Cytologia 25
A key made for the indentification of the fourteen species of Vigna is given below:
AA. Flower zygomorphic, posterior two sepals connate, keel curved,
not twisted.
aa. Flower small; seed oblong with caruncle, hilum excentric.
i) Flower yellow, habit viny.
ii) Calyx teeth shorter than tube.
Leaf linear-lanceolate, apex acutely obtuse, 7-8•~0.9-1cm.
.... V. parviflora Welw.
Leaf ovate-lanceolate, acute, 7-8•~1.0-1.2cm
.... V. wilmsii Burtt Davy
B) Calyx teeth equalling the tube
Leaf linear lanceolate, acute, 10.0-12.5•~0.8-1.2cm.
.... V. oblongifolia A. Rich.
iii) Flower blue, habit prostrate, leaf oval-rhomboidal, 1.9-2.3
•~ 1.6-2.3cm. .... V. gracilis Hooker
bb. Flower medium, seed 2-4mm, reniform, without caruncle,
hilum centric.
i) Fruit pendent.
Succulent, leaf thick, almost glabrous, ovate-rhomboidal,
obtuse, 5.6-7.3•~5.2-6.2cm.
.... V. marina (Burm.) Merrill.
Leaf hairy, ovate, acute, 6.0-8.5•~3-4cm.,,,,
V. luteola Benth.
ii) Fruit perpendicular to the axis.
Leaf valvety-hairy, ovate, with basal lobes, obtuse, 3.5-5.0•~
2.0-2.6cm. .... V. schimperi Baker
cc. Flower large, seed 5-12mm, oblong, reniform to subreni
form or sub-globese, without caruncle, hilum centric.
i) Fruit erect, 8-13cm, seed 4-5mm, erect bush.
.... V. catjang (Burm.) Walp. 1960 Cytotaxonomic Studies on Vigna 199
ii) Fruit pendent, 15-25cm, seed 6-10mm, prostrate or clim
bing..... V. sinensis (Linn.) Savi
iii) Fruit pendent, 30-60cm, seed 10-12mm, climbing vines.
.... V. sesquipedalis (L.) Fruw.
BB. Flower slightly irregular only due to twisting of the keel;
posterior sepals not connate, teeth larger than tube; leaf ovate with basal lobes, acuminate, 4.0-6.5•~3.8-5.0cm, viny.
.... V. membranacea A. Rich.
CC. Flower large, irregular ; posterior sepals not connate, keel
twisted.
Flower reddish violet; leaf ovate, acute, 5-8•~4-5.5cm.
Climbing, forming root tuber .... V. vexillata (L.) Benth.
Flower crimson; leaf ovate-lanceolate, 5.5-7.2•~1.4cm.
Procumbent, forming root tuber
.... V. devyi Bolus
Cytology
In six varieties of the three cultivated species and in the eleven other
species of Vigna, two chromosome complents were observed 2n=20 and 22.
In general, the chromosomes were small ranging in size from 1.6-3.7ƒÊ.
The chromosomes did not show much structural variation. All of them had
sub-median primary constriction. Three groups of chromosomes-long (3.7
- 3.0ƒÊ), medium (2.9-2.1ƒÊ), and short (2.0-1.6ƒÊ) could be distinguished.
Two pairs of chromosomes with satellite were observed in many somatic
complements.
Meiosis was studied in all the cultivated species and in seven other
species. It was regular in all of them. Two to three bivalents were found
to be attached with nucleolus at diakinesis in different species. Anaphasic
separation was found to be regular.
Some meiotic irregularities were however observed in the cultivated va
riety Poona of the species V. catjang. Though rarely, some cells showed
more than two spindles in anaphase II and consequent separation of chromo
somes in more than four poles. This has been described by us more in
detail in the meiosis of its induced tetraploids, where the phenomenon was
more exaggerated.
A comparative study of the chromosome complements of the different
species is given in Table 3 and shown in Figs. 6-33. Chromosomes are small
and the classification of long, medium and short are arbitrary. In several
specimens the satellited chromosomes could not be brought out in the pre
parations. The satellited chromosomes may be present in them, and a better technique to bring them out is necessary.
In V. sesquipedalis, V. parviflora, V. oblongifolia, V. gracilis, V.
schimperi, V. heterophylla and V. membranacea one long pair of chromo 200 N. K. Sen and J. G. Bhowal Cytologia 25
somes was found to be comparatively bigger (3.5-3.7 p) than it was in the rest of the species; where it was found to be 3.0-3.2ƒÊ long. A few species like V. ,racilis, V. heterophylla, V. membranacea, V. vexillata and V. davyi had 2 pairs of long
chromosomes in their
complements instead
of one pair found
in others.
Intercrossibility
The three culti
vated species V. sine
nsis, V. sesquipedalis
and V. catjang could
be easily crossed
among themselves.
The hybrids among
them were fertile
like inter-varietal
hybrids. Their F2
showed normal Men
delian segregation.
Most of the inter
specific hybridization
with the wild species
was done with V.
catjang of the culti
vated ones. Male
sterile plants from
the progeny of a
Figs. 1-19. 1-5, floral parts of Vigna species. 1, V. parviflora. Male-sterile•~Fertile 2, V. membranacea. 3, V. vexillata. 4, V. luteola. 5, V. catjang. 6-19, idiogramas of Vigna species. 6, V. sesquipedalis. 7, V. plant of the var. sinensis. 8, V. catjang. 9, V. parviflora. 10, V. wilmsii. Poona were used as 11. V. gracilis. 12, V. oblongifalia. 13, V. schimperi. 14, V. the female parent in murina. 15, V. luteola. 16, V. vexillata. 17, V. davyi, 18, many of the crosses. V. heterophylla.. 19, V. membranacea. A few crosses with the species V. luteola gave seeds but all crosses with the rest of the wild species were unsuccessful. The hybrid seeds of the cross V. luteola•~V. catjang were shrunken.
Another interspecific cross between the two wild species, V. luteola•~
V. parviflora gave some seeds which were very crumpled.
Results of fruit-setting in the different inter-specific crosses are given in
Table 4. 1960 Cytotaxonomic . Studies on . Vigna 201
Discussion
The chromosome numbers in two varieties of each of the three cultivated species of Vigna viz. V. Sinensis , V. catjang and V. sesquipedalis have been found to be 2n=22. Karpechenko (1925) re ported 2n=22 chromo somes for catjang and 2n=24 for sinensis and sesquipedalis. Rau (1929) reported 2n=24 chromosomes in 2 field varieties of V. catjang and in one variety of V. catjang variety sine nsis, which is probably V. sinensis. Whether varieties with 24 chro mosomes exist at all in the cultivated types cannot be said from the present study. But it may be concluded that 2n=22 chromosome ty pes are present in all the three cultivated species. The eleven wild species studied reveal two chromosome num bers in their somatic complements, 2n=22 and 2n=20. The spe Figs. 20-33. Somatic metaphase chromosomes of Vigna species cies V. parviflora, V. 20, V. sesquipedalis. 21, V. sinensis. 22, V. catjang. 23, . wilmsii, V. oblongi V. parviflora. 24, V. wilmsii. 25, V, gracilis. 26, V. ob folia, V. gracilis, V. longifolia. 27, V. schimperi. 28, V. marina. 29, V. luteola vexillata, V. davyi, V. 30, V. vexillata. 31, V. davyi. 32, V. heterophylla. 33, V. schimperi, V. marina membranacea. and V. luteola have 2n=22 chromosomes and V. heterophylla and V. membranacea have 2n=20 chromosomes in their somatic complements. Of these only chromosome numbers in V. vexillata and V. luteola were reported earlier. The other species of Vigna, whose chromosome numbers are known, are V. glabra, V. lanceotata, and V. owahnuensis.
The somatic chromosomes of all the species studied are small, 1.6ƒÊ to
3.7ƒÊ in length . The longest chromosomes vary in different species from 202 N. K. Sen and J. G. Bhowal Cytologia 25
Table 3. Chromosome complements of different species of Vigna
Table 4. Results of interspecific crosses
3.0ƒÊ to 3.7ƒÊ and the shortest chromosomes from 1.6ƒÊ to 2 .0ƒÊ in length. The small size of the chromosomes has been a great handicap in bringing out
details even with special techniques used for it. It appears that chromosome
complements of the 14 species are more or less similar , though in a few the satellited chromosomes could not be clearly distinguished . All the chromo
somes have submedian primary constriction , and the number of long, medium
and short chromosomes are more or less the same in all the species . It is seen that three chromosome numbers have been so far reported in
the genus Vigna: 2n=24, 22 and 20 . Excluding 2n=24 types, which could not be confirmed in this study and taking into consideration the numbers
observed here in nine new species , it may be concluded that most of the species of Vigna have 2n=22 chromosomes and three species have 2n=20 chromosomes. Which is the basic chromosome number in Vienna and how 1960 CytotaxonomicStudies on Vigna 203 the types with other chromosome complement arose cannot be said from this investigation. But from the evidence that the majority of the species of the tribe Phaseoleae consisting of the three allied genera Phaseolus, Dolichos and Vigna have 2n=22 chromosomes, it is likely that eleven is the basic chromo some number in Vig-na. Speciation through reduction in chromosome number often giving a des cending basic series has been demonstrated in many genera particularly in Crepis. Tobgy (1943) has shown that the 3-paired C. fuliginosa was derived from the four-paired C. neglecter or its ancestors through a system of recipro cal translocations. Sherman (1946) found that the four-paired C. kotschyana was derived in a similar manner from a five paired form related to C. fbetida. Morphologically the three species with 2n=22 chromosomes, V. ambacensis (Dusseau, 1941), V. heterophylla and V. membranacea are all more closely related to the various unconnected 2n=22 chromosome species, than they are to each other, like the three species with three pairs of chromosomes in Crepis viz. C. capillaris, C. fuliginosa and C. zacintha. Two of the 22-chromosome species in our collection viz. V. vexillata and V. davyi have perennial habit with tuberous root, a primitive character, and both the 20-chromosome species are annual. Considering all these it seems that the 20-chromosome species have been derived from the 22-chromo some ancestors. On the basis of their morphological characters the eleven wild species can be classified into 4 groups. The first group comprising of the species: V. parviflora, V. wilmsii, V. oblogifolia, V. heterophylla and V. gracilis, has a typically zygomorphic corolla, curved but not twisted keel and style and without any pouch like structure in the keel. The posterior two sepals are fused to give the false appearance of 4 sepals. Flowers are small. Seeds are small oblong with caruncle. Among these species V. parviflora, V. wilmsii and V. oblongifolia re semble one another very closely. Flowers are yellow, more or less of the same size. All the three species have viny habit. Shape and size of the leaves are however, conspicuously different. Leaves of V. parviflora are linear lanceolate with subacute apex, those of V. wilmsii are ovate-lanceolate with acute apex and those of V. oblongifolia linear-laneeolate with acute apex. V. gracilis is very closely related to these 3 species but differs in its prostrate habit and flower colour which is blue and in having small oval-rhomboidal leaves and small subterete fruits. V. heterophylla also have oblong seeds with caruncle but the seeds are bigger, The flowers are more or less of the same size, but bluish violet in colour. The plants are of viny habit with wooly linear ovate leaves having subacute apex. The second group consisting of V. luteola, V. marina and V. schimperi 204 N. K. Sen and J. G. Bhowal Cytologia 25 has reniform seeds without caruncle. Flowers are yellow and those of V, schimperi the biggest. All the three species have climbing habit V. marina is succulent with thick succulent almost glabrous leaves which are ovate rhombodial with obtuse apex. Leaves of V. luteola are lanceolate-ovate, thinly pubescent with acute apex. V. schimperi has hastately ovate leaves with acute apex. Hairs in leaves and fruits are very fine and thick giving velvety feeling. Fruits are borne at right angle to the axis. The third group consisting of two species: V. vexillata and V. davyi, has big flowers of same size, irregular corolla, one pouch like structure in the keel, and twisted keel and style; the flower is reddish violet in V. vexil lata and crimson in V. davyi. Fruits are also of same size and scabrous in both the species. Both of them have small reniform seed without caruncle. Formation of tuberous starchy root is characteristic of both the species. The two species can, however, be easily distinguished from their habit and leaf structure. V. vexillata is a climber and its leaves are ovate, while V. davyi is dwarf prostrate in habit with lanceolate-ovate leaves. V. membranacea with 2n=20 chromosomes is the lone member of the fourth group. It has some features in common with plants of both the second and third groups. It resembles the plants of the second group in its size of flower, which is apparently zygomorphic, without the one sided spur in the keel and non-tuberous root. But the flowers show some resemblance with those of V. vexillata and V. davyi of the third group in their slight twisting of the keel and style, and in their large calyx, in which the posterior two sepals are not fused. In its erect nature of fruits it also resembles the plants of the third group. The cultivated species V. sinensis (Linn.) Savi., V. catjang (Burm.) Walp. and V. sesquipedalis (Linn.) Fruw., though they differ markedly in character of fruit and habit, exhibit almost similar karyotypes and are easily intercrossable. The hybrids between them are fully fertile and show Men delian inheritance. It seems to be fallacious to consider them as distinct species. They can at the most be considered as the subspecies of a poly morphic species differing in many genes affecting both qualitative and quanti tative characters. Such species may be in the process of differentiation, which may lead to speciation if isolation of some kind is effective. Mackie's obser vation on the rank of these three groups as three subspecies of Vigna sinensis viz. V. sinensis, V. sinensis subspecies catjang and V. sinensis subspecies sesquipedalis is supported in this study. It is however felt that an appro priate subspecific name for the cowpea group should be given. The cultivated species have considerable similarity with the plants of the second group in their zygomorphic flowers, incurved untwisted keel and style and seeds without caruncle. The flowers are, however, much larger and red dish violet in colour. Among all the wild species of our collection V. luteola of the second group is most closely related to the cultivated species. It is the 1960 CytotaxonomicStudies on Vigna 205 only species which gave a few fruits in cross with the cultivated ones, and might have played some role in their origin. The ancestors of the cultivated species are likely to have trailing habit with small flowers, fruits and seeds. In the catjang group the flowers, fruits and seeds are the smallest and it seems to be under cultivation for much longer time than the other groups. But the plants are erect bush, and most of the wild species have a weak stem. The cowpea group has a trailing stem but the flowers and fruits are bigger. It seems that from a common ancestral stock, these two types have been gradually differentiated by selection. The sesquipedalis type with its extra long pods is likely to have been selected at a later stage from the plants of the cowpea type. On the cytological and morphological evidence it seems that four distinct phyla have diverged from a common ancestral stock. The first phylum comprises of the species V. parviflora Welw. V. wilmsii Burtt Davy., V. oblongifolia A. Rich. and V. gracilis Hook. The second consists of V. schimperi Baker., V. marina (Burm) Merrill., and V. luteola Benth. The cultivated V. sinensis with the subspecies are likely to have been derived from the second phylum. The third phylum includes the species V. vexillata (Linn.) Benth. and V. davyi Bolus. Morphologically the 20-chromosome species V. hetrophylla A. Rich. closely resembles the plants of the first group and are likely to have speciated from this stock. The other 20-chromosome species V. membranacea A. Rich. has characters common to plants of both second and third groups. Nothing more can be said about its ancestry, but as it has been assumed that the 20-chromosome plants have originated from the 22-chromosome types, as a tentative working hypothesis it is being assumed to have been derived from a group of 22-chromosome species, not present in our collection, with characters intermediate between second and third groups. The genus Vigna is very closely related to the genus Phaseolus. Pha seolus is distinguished from Vigna in its conspicuosly spirally coiled keel and style. The two species V. vexillata (Linn.) Benth. and V. davyi Bolus. of the third group have a somewhat twisted keel and style and an one-sided pouch in the keel i.e. have characters of both the genera. They may form a connecting link between Vigna and Phaseolus. Benthum and Mueller (1864) also have observed that by the obliquity of the flower and length of the beak V. vexillata is intermediate in some respects between Vigna and Phaseolus.
Summary 1. The eleven wild species of Vigna studied can be classified into four groups on the basis of their morphological affinities. i) In the first group comprising of the species viz. V. parvifloia Weiw., V. wilmsii Burtt Davy., V. oblongifolia A. Rich., and V. gracilis Hook. flowers are small zygomorphic, keel and style are not twisted, the posterior two sepals are fused and seeds are small oblong with caruncle. 206 N. K. Sen and J. G. Bhowal Cytologia 25
ii) The second group consisting of the three species viz. V. luteola
Benth., V. marina (Burm) Merr. and V. schimperi Baker differs from the
first group in having larger flowers and reniform seeds without caruncle.
iii) The plants of the third group consisting of the species V. vexillata
(Linn.) Benth. and V. davyi Bolus. have conspicuously large irregular flowers in which the posterior two sepals are not fused, keel slightly twisted with one
sided pouch, style slightly twisted tuberous root and seeds reniform without
caruncle.
iv) V. membranacea A. Rich. is the lone member of the fourth group
having several common features of both the second and third groups.
2. The plants of the third group in having slightly twisted keel with
one sided pouch also show their affinity to the genus Phaseolus.
3. The karyotypic study of the Vigna species has shown the presence
of two chromosome numbers 2n=22 and 2n=20. V. parviflora, V. wilmsii,
V. oblongifolia, V. gracilis, V. sehimperi, V. luleola, V. marina, V. vexil
lata and V. davyi and the cultivated species V. catjang, V. sinensis and V.
sesquipedalis have 2n=22 chromosomes. Only two species viz. V. hetero phylla and V. membranacea have 2n=20 chromosomes. 4. The chromosome number 2n=24 reported for V. catjang, V. sinensis
and V. sesquipedalis by some workers has not been observed in any of the
six varieties, two from each group, studied.
5. The chromosome complements of the fourteen species are more or
less similar in the number of long, medium and short chromosomes and in
their gross morphology.
6. The chromosmes of all the species are very small, ranging from 1.6
to 3.7ƒÊ in length and have submedian primary constriction. Long chromo
somes in the different species vary from 3.0 to 3.7ƒÊ and the short chromo
somes from 1.6 to 2.0ƒÊ.
7. Meiotic studies have shown regular pairing of the homologous chromo
somes forming bivalents in diakinesis and metaphase, and normal subsequent
meiotic stages.
8. The possibility of eleven as the basic chromosome number of Vigna
has been indicated. It has been assumed that the 2n=20 chromosomes type
V. heterophylla has been derived from the first group of species and the V.
membranacea from a 2n=22 chromosome group intermediate between the
second and the third groups.
9. The three cultivated types V. catjang, V. sinensis and V. sesquipedalis
need not be considered as distinct species but should be regarded as members
of a polymorphic species, V. sinensis with three subspecies viz, V. sinensis,
V. sinensis subspecies catjang and V. sinensis subspecies sesquipedalis.
10. They resemble the plants of the second group and are likely to have
been derived from them. V. luteola of that group is most closely related to
the cultivated species and is the only species that gave a few pods in crosses 1960 CytotaxonomicStudies on Vigna 207 with them. It seems that V. catjang and V. sinensis have been gradually differentiated from a common ancestral stock and V. sesquipedalis is a later selection from V. sinensis.
Acknowledgements This investigation has been possible with the generous help in the form of seed stockes of cultivated and wild species by the United States Depart ment of Agriculture. We have also received stocks from Dr . J. M. de Wet, South Africa; the Division of Plant Industry C. S. I. R. O. Australia; Director, Indian Agricultural Research Institute and our sincere thanks are due to all of them. We are also grateful to Dr. S. R. Sen Gupta, Director of the Institute for his keen interest in the project and to all members of the Agricultural Engineering Department for their active help.
Literature cited Benthum, G. and Mueller, F. 1864. Flora Australiensis. Lovel Reeve & Co., London: 258 -260. Darlington, C. D. and Wylie, A. P. 1955. Chromosomeatlas of flowering plants. George Allen and Unwin Ltd. London: 171. Dussesu, A. and Magnaut, C. 1941. Characteristiques caryologiques de Vigna ambacensis Welw C. R. Acad. Sci: 213, 276, Karpechenko,G. D. 1925. Bull. Appl. Bot. Pl. Breed. 14: 143 (Refer Darlington et. al 1955). Mackie, W. W. 1946. Black eye beans in California, Calif Agr. Exp. Sta. Bul.: 696. Merril, E. D. 1923. An ennumeration of Philippine flowering plants 2: 320. Oliver, D. 1871. Flora of tropical Africa. L. Reeve Co. London: 194-204. Piper, C. V. 1912. Agricultural varieties of the cowpea and immediately related species. U. S. D. A. Bur. P1. Ind. Bul. No. 229.- 1913. The wild prototype of the cowpea. U. S. D. A. Bur. Pl. Ind. Cir. 124: 29-32. Sherman, M. 1946. Karyotype evolution: a cytogenetic study of seven species and six in terspecific hybrids of Crepis. Univ. of Calif. Publ. Bot. 18: 369-408. Tobgy, H. A. 1943. A cytological study of Crepis fuliginosa, C. neglacta and their F1 hybrid, and its bearing on the mechanism of phylogeneticreduction in chromosome number. Jour. Genet. 45: 67-11. Tschechow,W. and Kartaschowa, N. 1932. Karyologisch systematisch Untersuchung der Tribus Loteae and PhaseoleaeUnterfam. Papilionatae. Cytologia 3: 221-249.