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Chromosome numbers in Pelargonium

 

1.    2.   3.   4   5.  

1. P.  odoratissimum               2. P. grossularioides                3. P. tomentosum         4. P. 'Graveolens' Argentina           5. P.x (hortorum) 'No.7'

            2n = 16                            2n = 38                                2n = 44                            2n=77                                        2n = 18

6.   7.  

 6.  P.x (hortorum) 'Vermelho'        7.  P.x (hortorum) 'Tojolo'

               2n = 18                                    2n = 36

Pelargonium Species        2n chromosome #    n chromosome #       Section  ()         Size  of Chromosome  

              P. ovale                            20                                   10                             Campylia                     small               

              P. exhibens                     22                                    11                             Chorisma                     large

              P. acetosum                    18                                     9                              Ciconium                     large

              P. frutetorum                   18                                      9                              Ciconium                     large

              P. inquinans                    18                                      9                             Ciconium                     large

              P. peltatum                      18                                      9                             Ciconium                     large

    P. zonale                          18                                      9                             Ciconium                     large

              P. echinatum                   22                                    11                             Cortusina                    small

              P. grandiflorum                22                                   11                             Glaucophyllum            small

              P. oblongatum                 22                                    11                            Hoarea                        small

              P. trifidum                         22                                    11                            Jenkinsonia               + large

              P. fulgidum                       22                                    11                            Ligularia                     small

              P. carnosum                     22                                    11                            Otidia                         small

              P. cucullatum                   22                                    11                            Pelargonium              small

              P. denticulatum               44                                    22                            Pelargonium              small

              P. capitatum                     66                                    33                           Pelargonium              small

              P. radens                          88                                    44                           Pelargonium              small   

              P. gibbosum                    22                                    11                            Polyactium                small

              P. exstipulatum               16                                       8                           Renformia                 small

              P. odoratissimum           16                                       8                           Renifomia                  small  

   P. endlicherianum           34                                     17                                       ?                     small

Some recurring patterns can be seen in the numbers of chromosomes. The haploid numbers fall into the sequence of n = 8, 9, 10, 11. Beyond that the chromosomes in sections () Ciconium, Chorisma and Jenkinsonia are much larger than those in the other sections. Within a section, i.e. Ciconium, most species have the same basic chromosome number.

Another pattern is well illustrated in Pelargonium where 2n = 22, 44, 66 and 88 depending on the species. The corresponding haploid numbers are 11, 22, 33 and 44. This is called a polyploid series. We would call 2n = 44 a tetraploid (four sets of 11), 2n = 66 is a hexaploid (six sets of 11), 2n = 88 is an octoploid (eight sets of 11).

Within a species we usually find that all plants have the same diploid chromosome number. Offspring are produced most of the time when the haploid number of chromosomes of the parents is the same. Seed production normally results when pollination occurs in these plants. When the haploid numbers of two parents are different hybridization is less likely. We do not expect that P. grossularioides with n = 19 will cross with P. carnosum with n = 11 and produce any seeds.

                                                                 

 

 

                         

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