The Commelina species contain metacentric, submetacentric and subtelocentric chromosomes with variation in number and morphology (Table 1).
C. africana
Somatic chromosomes observed from more than five intact cells showed that C. africana collected from Addis Ababa contained a diploid number of 2n=2x= 30. Because of its better chromosome spread and clear chromosome morphology a cell with 29 chromosome number is shown in Figure 1A and a karyotype constructed from same cell in Figure 1B. This variant of the species consisted of six pairs of metacentric chromosomes (pairs 1 to 6), five pairs of sub metacentic chromosomes (pair numbers 7 to 11) and four subtelocentrics (pairs 12 to 15) (Figure 1B). The karyotype formula is, therefore, 12m + 10sm + 8 st (Table 1). According to Stebbins karyotype classification, this species belongs to 2A type with asymmetry index of 65.19 (Table 1). Small satellites were also observed at the tip of the short arm of a pair of chromosomes (Figure 2A) and these correspond to the 8th pair on the karyotype (Figure 1B). Figure 2B shows three interphase nucleoli, from which it can be assumed that the maximum number of nucleoli and so chromosome satellites for this species is four.
Length wise measurement of metaphase chromosomes revealed a value range from the smallest 4.53µm to largest 7.5µm (Table 1). Total length of whole chromosome complement (2n) was 176.72µm. The chromosomes were medium in size with an average length and asymmetry of 5.89µm and 1.87, respectively.
C. benghalensis
According to somatic chromosome analysis of the root tips, this species possesses 2n=6x=66 (Figure 1C and Table 1). The karyotpe constructed based on calculated arm ratio and chromosome size revealed the presence of eighteen metacentric chromosome pairs (pair numbers 1, 3, 4, 5, 8, 11, 14, 15, 16, 18, 22, 24, 25, 29, 30, 31, 32, 33), twelve submetacentrics (pair numbers 6, 7, 9, 10, 12, 17, 19, 20, 21, 23, 27, 28) and 3 subtelocentric pairs (pairs 2, 13, 26 ) (Figure 1D). The karyotype formula was, therefore, 36m + 24sm + 6st. As to Stebbins method of classification, C. benghalensis possesses asymmetry index of 62.58 with 2B in karyotype asymmetry (Table 1). A maximum of five nucleoli were observed through silver staining but no satellites were observed (Figure 1E). Two of the nucleoli are much larger than the other three nucleoli. Each of the larger nucleoli might have resulted from fusion of two or more nucleoli. It can be inferred that six or more chromosome satellites are present in this species.
The chromosome lengths differ from the smallest 2.5µm and gradually increased up to the largest 5.625µm (Table 1). The total length of whole chromosome complement was about 267.935µm (Table 1). The total length of the long arms of the diploid set was 167.675µm and that of short arms for diploid set was 100.26µm with their ratio generating an average karyotype asymmetry of 1.672. Generally, C. benghalensis (Addis Ababa) has predominantly metacentric and submetacentric type of chromosomes. The chromosomes were short to medium in size with an average length of 4.06µm.
C. diffusa from Ginchi
The variant of C. diffusa collected from Ginchi possessed 2n= 66 (Table 1 and Figure 1E). Based on centromeric ratio and chromosome length measurements , the karyotype (Figure 1F) consisted of fourteen metacentric pairs (pair numbers 1, 4, 6, 15, 16, 20, 21, 23, 25, 26, 30, 31, 32, 33), thirteen submetacentrics (pairs 2, 3, 5, 7, 8, 9, 10, 13, 17, 19, 24, 27, 28) and six subtelocentrics (pairs 11, 12, 14, 18, 22, 29) with a formula of 28m + 26sm + 12st. The asymmetry index is 65.56 and belongs to 2B type of Stebbins karyotype classification (Table 1).
As shown in Figure 2(C and D), a total of six satellites and four nucleoli were observed from chromosome preparation and silver staining, respectively. Size of satellites varies with one pair being larger than the other two.
C. diffusa (Ginchi) has comparatively larger chromosomes than the other Commelina species included in this study with a length range from smallest 4.375µm to largest 11.25µm and total length of whole chromosome complement 507.53µm (Table 1). The total length of long arms and short arms for the diploid set was 332.745µm and 174.785µm respectively (Table 1). The average karyotype asymmetry is 1.904 and on the average the chromosomes can be classified under submetacentric. The chromosomes were medium to large in size with an average length of 7.69µm.
C. diffusa (Ginchi) has intrachromosomal and interchromosomal asymmetry indices of 0.435 and 0.17035 respectively (Table 1). This variant also has a coefficient of variation in chromosome length of (17.035), ratio of centromeric gradient (53.0163) and dispersion index (9.031) (Table 1).
Table 1 Cytological analysis of Commelina L.
Species

Chromosome length (µm)
Shortest: longest

ACL (µm)

2n

Basic number(x)

Ploidy level

A1

A2

Cv

CG

DI

Karyotype Formula

Number of metaphase plates

Asymmetry index

Stebbins asymmetry

K

L

M

C. africana

4.53 – 7.5

5.89

30

15

2x

0.4345

0.1498

14.98

55.32

8.29

12m + 10sm + 8st

10

65.19

0.43

1.67

2A

C. benghalensis

2.5 – 5.625

4.06

66

11

6x

0.3715

0.1582

15.82

57.831

0.3715

36m + 24sm + 6st

4

62.58

0.35

2.25

2B

C.diffusa (Ginchi)

4.375 – 11.25

7.69

66





0.435

0.17035

17.035

53.0163

9.031

28m + 26sm + 12st

5

65.56

0.5

2.57

2B

C.diffusa (Jimma)

2.5 – 4.58

3.47

30

15

2x

0.76717

0.13771

13.771

39.32

5.415

10m + 8sm + 12st

10

69.497

0.67

1.832

3A

C. subulata

1.923 – 3.654

2.77

30

15

2x

0.3523

0.1891

18.91

67.45

0.3523

18m + 10sm + 2st

4

60.232

0.267

1.9

2A

ACL: average chromosome length; 2n: somatic chromosome number; A1: intrachromosomal asymmetry index; A2: interchromosomal asymmetry index; Cv: Coefficient of variation of chromosome length; CG: ratio of centromeric gradient; DI: dispersion index K: percentage of chromosome with ratio=r>2;
L: ratio of largest to smallest chromosome; M: degree of asymmetry
C. diffusa from Jimma
The material of this species collected from Jimma possessed 2n=2x= 30 (Table 1 and Figure 1G). According to centromeric ratio and chromosome length measurements, the karyotype (Figure 1H) has five metacentric pairs (pair numbers 1 to 5), 4 submetacentric pairs (pairs 6 to 9) and 6 subtelocentric pairs (pair numbers 10 to 15) with a formula of 10m + 8sm + 12st. The asymmetry index is comparatively higher than the other studied Commelina species with a value of 69.497 and according to Stebbins karyotype asymmetry classification, C. diffusa (Jimma) belongs to 3A type (Table 1).
Even if no satellites were observed from the current plant material, a total of three interphase nucleoli were observed that possibly predict the number of NORs or satellites to be four (Figure 2F).
C. diffusa (Jimma) possesses the smallest chromosomes size next to C. subulata with a length range from shortest 2.5µm to longest 4.58µm and total length of whole 2n chromosome complement 104.22µm (Table 1). The total length of long arms for the diploid set was 72.43µm and total length of short arms for the diploid set was 31.79. The chromosomes range from very small to medium in size with an average length of 3.47µm and karyotype asymmetry of 2.28µm.
This particular variant has the highest value in terms of intrachromosomal asymmetry index (0.76717). It also possesses the lowest interchromosomal asymmetry index (0.13771), coefficient of variation in chromosome length (13.771), ratio in centromeric gradient (39.32) and dispersion index (5.415) when compared to values from all other studied plants of the genus Commelina.
C. subulata
The experimental species collected from Ginchi indicated that C. subulata has a diploid number of 2n =2x= 30 (Table 1 and Figure 1I). As to arm ratio and chromosome length measurements, the karyotype (Figure 1J) consisted of nine metacentric pairs (pair numbers 1, 2, 3, 5, 8, 9, 10, 12, 13), five submetacentrics (4, 6, 11, 14, 15) and one pair of subtelocentrics (7) with a karyotypic formula of 18m + 10sm + 2st. The species possesses the lowest value in asymmetry index (60.232), being the 2A type in Stebbins asymmetry classification (Table 1). Two interphase nucleoli were observed (Figure 2G), but no satellites were observed. One of the two nucleoli is larger than the other, which could result from fusion of two or more nucleoli; and it may be inferred that a total of four satellite chromosomes/ NORs are present.
Commelina subulata (Ginchi) has the smallest chromosome size than other species included in this study with a length range from smallest1.923µm to largest 3.654µm and the total length of whole chromosome complement is 83.154µm (Table 1). .
The total length of long arms and short arms for the diploid set was 50.085µm and 33.069µm, respectively (Table 1). The average karyotype asymmetry is 1.51 and the chromosomes, on the average arm ratio, can be considered as metacentric. The chromosomes are very small to medium in size with an average length of 2.77µm.
C. subulata possesses the lowest intrachromosomal asymmetry index, highest ratio of centromeric gradient and dispersion index with a value of 0.3523, 12.755 and 67.45, respectively. The species also consisted of an interchromosomal asymmetry index (0.1891) and coefficient of variation in chromosome length (18.91) (Table 1).