Species
Cassiope tetragona (L.) D. Don., common name Arctic Bell Heather,
is an evergreen dwarf shrub of the Ericaceae family. The species has a
hemi-prostrate growth form and reaches heights of up to 10-15 cm at the
research site, but can grow up to 30 cm tall when supported by, for
example, rocks. It is the dominant species in prostrate/ hemi-prostrate
dwarf-shrub tundra, but less so in the erect dwarf-shrub tundra as found
at the research site, and has a circumarctic distribution . It occurs in
the northernmost polar desert at 83 °N in northern Greenland , where it
is the most common heath-forming species . In western Greenland it is
found as far south as 63.35 °N, but towards the south only at alpine
sites or on north-facing slopes . The species’ leaves are attached to
its stems in opposite pairs, which alternate in 90° angles resulting in
four rows of leaves (hence tetragona ). Leaf lengths rapidly
increase at the beginning of the growing season and decrease thereafter,
resulting in a wave-like pattern with each wave representing a single
growing season . The discovery of so-called wintermarksepta , i.e. dark
bands coinciding with lows in leaf lengths visible in lateral
cross-sections of C. tetragona branches, has enabled the
construction of >century-long growth chronologies . WMS
consist of green and with increasing age, brown lignified meristem cells
(see Fig. S1).