Classifying plants

The resurrection plant, Myrothamnus flabellifolius: one species or many? by John P. Moore, Jill M. Farrant, George G. Lindsey and Wolf F. Brandt, Department of Molecular and Cellular Biology, University of Cape Town

LEFT: Myrothamnus flabellifolius plants growing in the north-west of Harare, Zimbabwe. RIGHT: Dead or alive? The resurrection plant, Myrothamnus flabellifolius.

Resurrection plants possess the abil- rection plants are either grasses (like Having evolved in the Late Cretaceous ity to survive extreme drought by losing Xerophyta and Eragrostis) or small her- period during the evolution and radiation most of their water and existing in a baceous plants (like Craterostigma). It is of most angiosperm families, M. flabel- seemingly dormant state for various also one of the more interesting species, lifolius possesses a unique combination lengths of time. After the summer rain- as it appears to belong to a very ancient of morphological and reproductive fea- fall, its seemingly dead and dried-up angiosperm lineage. Recent DNA evi- tures which prevents a simple system- leaves return to a green, fully hydrated dence suggests that it split off from its atic classification and taxonomic place- state and it continues to grow normally. closest relatives in the genus Gunnera ment. Currently M. flabellifolius resides One of southern Africa’s best-known over 100 million years ago. Ironically in its own family, the Myrothamnaceae. resurrection plants is Myrothamnus fla- whilst M. flabellifolius is a small-leaved, It is possible that during the diver- bellifolius. woody shrub, its nearest relative in sification of the angiosperms during Myrothamnus flabellifolius is a rel- Africa is Gunnera perpensa, a large- the Cretaceous period, M. flabellifolius atively large woody shrub, which is leaved, aquatic plant commonly known became saddled with a combination unusual as most of the other resur- as the water pumpkin! One might won- of morphological features not gener- der how a small-leaved, desiccation-tol- ally found in other angiosperm families. erant plant evolved from a large-leaved, These features subsequently became aquatic ancestor. However, there is modified and used to help the plant a rare and endemic Namibian aquat- overcome the problems of extreme des- ic resurrection plant Chamaegigas iccation. intrepidus (a member of the snapdragon The first attempt at systematic clas- or Scrophulariaceae family) that grows sification of the various populations of in rock pools that dry up periodically, M. flabellifolius was attempted by the which can survive desiccation and also Swedish botanist, Henning Weimarck, tolerate being completely submerged. in 1936. He admitted that M. flabellifo- lius was a phenotypically very diverse species and that this proved difficult LEFT: An inselberg between Mueda and Montepuez in delineating the various populations. in Mozambique. He decided not to assign new spe- cies to the genus but rather to clas-

September 2007 Veld&Flora 161 tions of sensu stricto were also present. flat rock plateaus consisting of. gran- Later C. Puff re-appraised this clas- ite, shale, quartz or sandstone. South sification by suggesting that M. flabel- African and Zimbabwean plants occur lifolius elongata and sensu stricto were in regions experiencing annual summer morphologically indistinguishable. rainfall and tend to be found growing An initial study of phenolic and genetic on rock plateaus where water run-off variation amongst populations in South is quite rapid. Consequently the root Africa and Namibia revealed that all the systems of the plants are quite shal- Namibian populations were similar to low. Namibian plants occur in much each other but completely distinct from more arid regions experiencing irregu- populations collected in South Africa. lar summer rainfall, possibly every two DNA evidence suggested that the two or more years. These plants grow on ABOVE: Myrothamnus flabellifolius plants growing on populations diverged from each other rock inselbergs with extensive crevices the slopes of an inselberg in Mozambique. around four million years ago. This in the rock face that tend to trap water, may have been due to a combination and the plants possess extraordinarily BELOW: Variation in leaf size. From left to right: The leaves of plants sourced from Zimbabwe, South of geographical (desert, inselbergs) and extensive root systems that extend into Africa, two from Namibia, Malawi and Mozambique. climatic (rainfall variation) conditions these crevices. that prevented gene flow between the Plants from Mozambique and Malawi two populations. occur in a generally wetter climate than Recently we have collected plants the other populations, which may allow from various locations in South Africa, a number of growing periods during the Namibia, Zimbabwe, Mozambique wetter months of the year compared to and Malawi. The morphological varia- the annual or less than annual growth tion amongst the populations is quite periods that occur in South Africa and striking. Whereas plants sourced from Zimbabwe and in Namibia respectively. South Africa and Zimbabwe are gener- The large size of these plants may there- ally smaller, with small leaves, those fore reflect an adaptation to more regu- sourced from Mozambique and Malawi lar growth periods. These larger plants are much larger, with thick stems and also have extremely thick woody central large leaves. Two variants of these stems, which indicate that the plants larger plants seem to exist, one consist- are quite old (easily 50-100 years). sify these variants as subspecies. He ing of large leaves with a thick bushy Unfortunately it has proved difficult divided M. flabellifolius into three differ- stipule sheath and another composed of to age the plants using dendrochrono- ent subspecies, namely elongata, sensu large leaves but with a thin and simple logical techniques, according to Dr Ed stricto and robusta, based on mor- stipule sheath. In Namibia the plants February, as they do not produce con- phological characteristics. Some of the seem to be of intermediate size with ventional tree ring patterns. Leaf litter, subspecies did not correlate with their longer leaves than those found in South mammal droppings and other debris geographical location as elongata and Africa and Zimbabwe. are observed to accumulate around the sensu stricto occurred on both sides The climate and geology of the regions base of many M. flabellifolius colonies. of the Kalahari Desert divide. Robusta where the populations are found are We believe this debris may provide an occurred predominately in the north- quite different. M. flabellifolius is gen- important source of nutrients. east of Mozambique, although popula- erally located on rocky inselbergs or We propose that at least five subspe-

BELOW: The small leafed branches from plants sourced in South Africa BELOW: A branch from a plant growing on the inselberg between Mueda (Myrothamnus flabellifolius sensu stricta) (top) and a possible new subspe- and Montepuez in Mozambique (M. flabellifolius robusta). This is from a cies from Zimbabwe (bottom). female plant as the dried ovaries and seed pods are visible.

162 September 2007 Veld&Flora cies of M. flabellifolius occur in Southern Africa that have adopted similar but not What does that mean? identical strategies to colonize a range of inhospitable habitats. Plants from angiosperm flowering plants Zimbabwe and Mozambique are so dif- ferent from each other and from plants dormant lying inactive, waiting for a cue to resume active growth from Namibia and South Africa that genotype describes the genetic constitution of an individual, usually with reference to a they may represent new species in the specific character under consideration genus. It is also evident that even with herbaceous plants that are soft and not woody morphologically similar plants from hydrated containing water Namibia and South Africa that there exists phenolic and genetic variation. In inselberg (from German Insel - island, and Berg - mountain) an isolated, rocky hill that addition there is a rare and little known stands above the surrounding plains and appears like an island relative, M. moschata, which grows in Late Cretaceous Period (100 - 65 million years ago) refers to the second half of the Madagascar. It would thus appear that Cretaceous Period, one of the major divisions of the geological timescale a new classification of M. flabellifo- morphology the study of the form and shape of the plant lius throughout its geographic range is phenolic and genetic studies using easily observable phenotypes to deduce a plant’s needed. This has relevance to conserva- genotype and to help hypothesize about how individual genes function. (One can know tion strategies to protect regional popu- about phenotype by observing the outward appearance of an organism, one can know about lations against excessive collection for genotype by observing its DNA) medicinal and commercial usage. phenotype (from Greek: pheno - appearing, and type - sort or kind) describes one of an Further reading individual plant’s traits or characteristics that is measurable (like small leaves), and that is Moore, J.P., Lindsey, G.G., Farrant, J.M., Brandt, W.F. expressed in only a subset of the individuals within that population 2007. An overview of the biology of the desiccation- phenotypically grouping plants according to their phenotype (e.g. all small leaved plants tolerant resurrection plant Myrothamnus flabellifolius. within a species are grouped together) Annals of Botany 99, 211-217. systematic classification the study and description of the variation in living organisms and Moore, J.P., Farrant, J.M., Lindsey, G.G., Brandt, the relationships that exist between them W.F. 2005 The South African and Namibian popula- taxonomy the study of the principles and practices of the classification of the natural world, tions of resurrection plant Myrothamnus flabellifolius which includes the practice of systematic classification are genetically distinct and display variation in their galloylquinic acid composition. Journal of Chemical woody shrub a plant that has a perennial (living for two years or longer) stem that is above Ecology 31, 2823–2834. ground and covered by a layer of thickened bark

LEFT: Myrothamnus flabellifolius plants growing on rocky terrain at Karibib in Namibia.

BELOW: The Khomas Hochland area to the west of Windhoek, Namibia, showing resurrection plants growing on a slope after some rain had fallen, but unfortunately not enough to resurrect all of the Myrothamnus flabellifolius plants.

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