Grassroots Vol 20 No 3 | Page 22

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