The Brevivalvula section of the grass polyploid complex Pennisetum shows va
rious reproductive systems, apomixis being the most widespread. Haplotype v
ariation of chloroplast DNA was studied in the six morphological taxa (spec
ies) of this section by using RFLP analysis in 54 plants corresponding to 1
4 elementary taxa, each characterized on the basis of morphology and ploidy
level. Two additional species, Pennisetum glaucum and P. purpureum, which
belong to another section of the same genus, were analysed for comparison.
In Brevivalvula, chloroplast DNA size was estimated to range between 130 an
d 133 kb. Thirteen of 15 distinct haplotypes identified in the study were s
pecific to the Brevivalvula section. They were unequally distributed among
the morphotypes, the ploidy levels and sampling sites. Within the Brevivalv
ula section, plants of P. setosum, which are perennial and reproduce vegeta
tively or by agamospermy, possessed a single specific haplotype. This speci
es differed clearly from the five other morphological species, which are kn
own to be annual, to show either sexual or agamospermic reproduction and wh
ich shared most of the 12 other haplotypes observed in the section, suggest
ing the occurrence of multiple hybridization events between the taxa. Chlor
oplast DNA variation was highly geographically structured, suggesting low s
eed dispersal between sites, whereas the substantial haplotype diversity ob
served in the sites may indicate that agamic reproduction is responsible fo
r the maintenance of distinct genetically isolated clones. Haplotype classi
fication using Wagner's parsimony suggested the occurrence of bidirectional
gene flow between the diploids and the polyploids, as reported already in
other related apomictic complexes.