Grassroots Vol 20 No 3 | Page 21

Underground trees of the Highveld Richard Gill Current Address: Johannesburg E-mail Address: [email protected] FEATURE What are underground trees? Botanically, an underground tree is referred to as a geoxylic suffrutex; where geoxyle refers to a subterranean woody plant with the bulk of its biomass below ground, and a suffratex is a shrub with a woody underground base and is also known as a subshrub or dwarf shrub. Often only the tips of their woody branches (ramets) protrude aboveground, to support their leaves and flowers. They are commonly referred to as geoxyles or geosuffs. With their underground storage organs and bud-banks (accumulation of growth buds able to sprout in future) safely below ground, they are able to resprout quickly after disturbances such as fires (Figure 1), frost or grazing, and it is thought that some of them can live extraordinarily long lives. As a result, many of them produce very few seeds, and young plants are rare. Figure 1: A recently burnt firebreak near Tarlton, exposing part of a “forest” of Sand Apple, Parinari capensis. Note how quickly they resprout after fire. 2a 2d Professor Braam van Wyk, University of Pretoria, asked about a video suggesting a specimen of Sand Apple (Parinari capensis) in Pretoria is around 13 000 years old, suggested ages in excess of 10 000 years are quite possible for some specimens, and some may be considerably older: “The shoots die and renew continuously, but the clone persists. Now if an underground tree is essentially immortal, then it would certainly not be unrealistic to hypothesize that some clones in our Highveld grasslands may be as old as the grasslands in that area themselves. Hence I suspect that some of the larger underground tree clones in southern Africa may be much older than the 13000 years mentioned.” 2b 2c 2e While there are challenges with determining their ages, Lynch et al. (1998) used radiocarbon dating, molecular markers and chromosome counts to estimate the age of a 1200 m wide clone of Lomatia tasmanica, in Tasmania, at 43 600 years old. While technically more Figure 2: Erythrina zeyheri. Klipriviersberg Nature Reserve (a,b,c), and roots exposed after flooding - Bethal area (d,e) © Paul Meintjies Grassroots Vol 20 No 3 September 2020 20