FEATURE
an underground shrub than an underground
tree, this illustrates nicely how
geoxyles are able to live a long time.
Pando, a massive clone of more than 40
000 genetically identical Quaking Aspen
trees in Utah, and the extensive Miombo
woodlands in southern Africa are further
examples of extreme longevity in clonal
tree species. If clonal terrestrial trees
can attain such great ages exposed to
the elements above the ground, then
there is little to suggest that subterranean
species shouldn’t equally be so
old protected below ground.
What drove them underground?
Most species occur in the savannahs of
sub-equatorial Africa, and Brazil. Studies
in both these areas reveal they began
evolving along with the spread of
the savannahs during the last 8 million
years, with many evolving as recently as
3-2 mya. There has been much debate
3a
about what drove them underground.
Arguments have been put forward for
various factors such as fires, frost, grazing,
poor nutrients and seasonally waterlogged
areas.
Maurin et al. (2014) concluded that
geoxyles “may have evolved in response
to the interactive effects of
frequent fires and high precipitation.
As such, geoxyles may be regarded as
markers of fire-maintained savannas occurring
in climates suitable for forests.”
Lamont et al. (2017), working with the
Protea genus, conclude that fire was the
main driving factor and that frost may
have had a later influence.
Maurin et al. (2014) mention 267 geoxyles
in sub-equatorial Africa. The photographs
in this article are some of the
more commonly found species on the
Highveld.
3b
5a
3c
5b
Figure 3a-3c: Elephantorrhiza elephantina. Crocodile River Nature Reserve, Suikerbosrand
NR, and Klipriviersberg NR
4a
4b
Figure 4a & 4b: Parinari capensis. Kloofendal NR, and with exposed root in Muldersdrift
Figure 5a & 5b: Rotheca hirsuta.
Crocodile River NR
21 Grassroots Vol 20 No 3 September 2020