A PHYLOGENETIC STUDY OF SPHAGNUM SUBGENUS SPHAGNUM BASED
ON PLASTID SEQUENCES
Elizabeth De Smet and Dr. Eric F. Karlin
School of Theoretical and Applied Sciences of Ramapo College of New Jersey
INTRODUCTION
• The genus Sphagnum (peat
moss) is the most ecologically and
economically significant group of
bryophytes (1). The genus is
divided into six subgenera (2), with
one being the subgenus
Sphagnum, which is found globally
(3-16). Both haploids and
allopolyploids are present within
the subgenus (13-16). The parental
species of the allopolyploids have
not been determined . Although
based on a small sample size, a
prior phylogenetic study suggests
that two divergent groups occur in
subgenus Sphagnum (2).
89.9
Clade A
OBJECTIVE
• To study the evolutionary history
of the subgenus Sphagnum using
plastid sequences.
METHODS & DATA ANALYSIS
• Twenty-nine trnL-trnF plastid
sequences from 14 species in
subgenus Sphagnum were
obtained from Genbank (17).
• These sequences were
used in six previous
studies (18-23).
• The sequences were entered into
the program Geneious (24) for
sequence alignment and initial
phylogenetic analysis.
• Phylogenetic trees were
constructed from the
sequence alignments, using
the HKY nucleotide
substitution model and
Neighbor Joining analysis.
• Sphagnum strictum
(subgenus Rigida) was used
as an outgroup
• Reliability of each inferred
tree was tested with1,000
bootstraps.
85.1
Clade B
Figure 1: Cladogram showing the genetic relationships among species in Sphagnum subgenus Sphagnum based on the trnL – trnF
locus (plastid DNA). Allopolyploid species are highlighted in blue.
Table 1: Global distribution of the Sphagnum species studied listed by clade. (3-16)
Species
N. America S. America Eurasia S.E. Asia E. Asia Australia Africa
Clade A
alegrense
X
?
aureum
X
brasilience
X
brevirameum
X
X
centrale
X
X
X
cristatum
X
cuculliforme
X
X
magellanicum
X
X
X
X
X
X
palustre
X
papillosum
X
X
X
X
pericheatiale
X
X
X
X
X
portoricense
X
X
Clade B
affine
X
X
X
austinii
X
X
imbricatum
X
X
X
X
steerei
X
Oceania
X
X
Photo by Dr. Eric F. Karlin
RESULTS TO DATE
• Phylogenetic analysis shows
two well-supported clades (Fig. 1,
Table 1).
• Both clades show some degree
of internal genetic diversification.
• Clade A has 12 species, with
both haploids and allopolyploids
being present (Fig. 1, Table 1).
• Clade B contains four species;
all are haploids (Fig. 1, Table 1).
• The allopolyploids S. centrale &
S. palustre are genetically close to
the haploid S. magellanicum (data
not shown)
• Sphagnum affine (in yellow)
appears in both clades.
PRELIMINARY CONCLUSIONS
• There are two divergent lines in
subgenus Sphagnum, conforming
with the finding of Shaw (2).
• Plastid DNA in Sphagnum is
inherited maternally (25). This
suggests that S. magellanicum may
be the maternal parent of the
allopolyploids S. centrale and S.
palustre.
• Species in Clade B all share a
similar microscopic cell structure
(26-27) that is distinct from species
in Clade A.
• There is no morphological
character that distinguishes Clade
A species as a group.
• As Clade A has more species, a
wider geographic distribution, and
a greater range of morphological
variation, it appears to be the older
clade.
• The presence of Sphagnum affine
in both clades needs further study.
It may be a sampling error or it
could indicate hybridization.
Photo by Matt Johnson
Figure 2: Pictures of species in Sphagnum subgenus Sphagnum
Left S. cristatum of Clade A, Right S. austinii of Clade B.
LITERATURE CITED
See attached pages