De. Soltis et al., Phylogenetic relationships and evolution in Chrysosplenium (Saxifragaceae)based on matK sequence data, AM J BOTANY, 88(5), 2001, pp. 883-893
Chrysosplenium (Saxifragaceae) consists of 57 species widely distributed in
temperate and arctic regions of the Northern Hemisphere, with two species
restricted to the southern part of South America. Species relationships wit
hin the genus are highly problematic. The genus has traditionally been divi
ded into two groups, sometimes recognized as sections (Oppositifolia and Al
ternifolia), based on leaf arrangement, or, alternatively, into 17 series.
Based on morphological features, Hara suggested that the genus originated i
n South America and then subsequently migrated to the Northern Hemisphere.
We conducted phylogenetic analyses of DNA sequences of the chloroplast gene
matK for species of Chrysosplenium to elucidate relationships, test Hara's
biogeographic hypothesis for the genus, and examine chromosomal and gynoec
ial diversification. These analyses revealed that both sections Oppositifol
ia and Alternifolia are monophyletic and form two large sister clades. Henc
e, leaf arrangement is a good indicator of relationships within this genus.
Hara's series Pilosa and Macrostemon are each also monophyletic; however.
series Oppositifolia, Alternifolia, and Nepalensia are clearly not monophyl
etic. MacClade reconstructions suggest that the genus arose in Eastern Asia
, rather than in South America, with several independent migration events f
rom Asia to the New World. In one well-defined subclade, species from easte
rn and western North America form a discrete clade, with Old World species
as their sister group, suggesting that the eastern and western North Americ
an taxa diverged following migration to that continent. The South American
species forms a clade with species from eastern Asia; this disjunction may
be the result of ancient long-distance dispersal. Character mapping demonst
rated that gynoecial diversification is dynamic, with reversals from inferi
or to half-inferior ovaries, as well as to ovaries that appear superior. Ch
romosomal evolution also appears to be labile with several independent orig
ins of n = 12 (from an original number of n = 11) and multiple episodes of
aneuploidy.