|Nepenthaceae are remarkably uniform in
chromosome number with 2n=80. There is good evidence that x=5
(x=10) is the basic chromosome number for the family.
size, condensing behaviour of chromatin and interphase nuclei are very similar
to that of Droseraceae.
Chromosome numbers of
selected species of Nepenthes
Investigated species: all 2n=80
Nepenthes madagascariensis, N. pervillei,
N. distillatoria, N. khasiana, N. rafflesiana, N.
truncata, N. stenophylla, N. gracilis, N. eymai, N.
thorelii, N. veeitchii, N. albomarginata, N.
reinwardtiana, N. tentaculata
chromosomes of 6 species of Nepenthes:
- N. madagascariensis
B - N.
pervillei C -
D - N.
rafflesiana E -
N. distillaroria F
- N. albomarginata
A cytological comparison
Nepenthaceae - Droseraceae
Recent molecular studies and
cladistic analysis of rbcL data (ALBERT et al. 1992;
CHASE et al. 1993) indicate that Nepenthaceae may be
surprisingly closely allied to Droseraceae and also to the Caryophyllales.
These affinities of Nepenthaceae and Droseraceae are strongly supported
by the cytological data. Both families share common karyomorphological
All chromosomes are generally very small in size and only in
Droseraceae a classification in small, medium andflarge chromosomes (or
karyotypes) is possible.
The condensing behaviour, the chromatin and
interphase nuclei structure is also very similar.
In contrast to
Droseraceae which probably lack a primary constrictions (KONDO & LAVARACK, 1984) centromeres
have been observed in the larger chromosome of Nepenthes.
the most frequent basic number appears to be x=5 (x=10), being found in many
taxa especially in Drosera subg. Drosera.
In other sections of Drosera
various chromosome numbers have been reported (KONDO
1966; 1969; 1970; 1971; 1973; 1976; 1984) with primary basic numbers x=6,7,8,9
and perhaps also secondary basic numbers x=11 and x=13.
seems very common especially in some Australian groups of Drosera.
the related genera Dionaea and Aldrovanda x=8 has been
established and for the genus Drosophyllum the basic number x=6 is
It is remarkable that Droseraceae as well as Nepenthacae have
reached the same ploidy level (8x or 16x). Available data suggest x=5 or x=10
may be ancestral for both families.
All available data show that
Droseraceae exhibit an enormous spectrum of chromosome numbers.
Hybridisation, parallel polyploidisation on different base numbers an
numerical changes were probably involved in the evolutionary process.
It is evident that in Droseraceae all ploidy levels are present,
whereas in Nepenthes diploid and lower polyploids have already gone extinct and
the radiation was restricted to a high ploidy level.
In view of the
phylogenetic background one can assume that Nepenthaceae are palaeopolyploids
with the basic number x=20.
The loss of taxa with lower ploidy levels,
the high chromosome number, the isolated taxonomic position, the palaeotropic
distribution, the uniformity in many characters and the reduced genetic
variability support this assumption.
On the other hand, fossil record,
the specialized morphology and molecular data are not in favour of this
In view of the molecular data (rbcL), palynological
(tetrads), chemical (naphthochinons) and morphological features (fruit, seeds,
embryo, ovules) and also from the cytological point of view a systematic
position of the Nepenthaceae not to far away from the Droseraceae is
Summary of chromosome numbers,
ploidy levels and basic numbers ascertained
for Nepenthaceae and