Earth & Environmental Sciences
Permian
100%
flora
63%
extinction
38%
mass extinction
33%
xylem
29%
new genus
23%
stem
23%
Lopingian
21%
seed
21%
Pennsylvanian
21%
environmental change
19%
phylogenetics
18%
radiation
16%
indicator
15%
cladistics
14%
climate change
13%
ocean
13%
land
12%
Guadalupian
12%
fossil
10%
Sakmarian
9%
loss
9%
plant species
9%
volcanism
8%
maturation
7%
floristics
7%
province
7%
organ
7%
young
6%
plant community
6%
peat
6%
competition (biological)
6%
coniferous tree
5%
topology
5%
flood basalt
5%
symmetry
5%
pollen
5%
Agriculture & Biology
China
44%
flora
38%
ovules
32%
new genus
21%
case studies
19%
secondary xylem
18%
stems
16%
phylogeny
15%
xylem
13%
Permian period
13%
fossils
9%
coal
8%
peat
8%
Spermatophytina
7%
Guadalupian epoch
7%
fronds
7%
plant communities
7%
tuff
7%
resin canals
6%
wetland plants
6%
integument
6%
pith
5%
vascular bundles
5%