Fynbos oddity The Pacific face of fynbos? Metrosideros angustifo/ia is one of the most ordinary looking of shrubs in the fynbos, but is apparently derived from wei rd plants on Pacific islands such as bog bonsais, woody creepers and forest stranglers. by Antoni V. Milewski, Percy FitzPatrick ABOVE: The seed bearing capsules of Metrosideros angustifolia resemble tiny fragile versions of those of Eucalyptus betraying the fact that this is the only Indigenous member of the Myrtaceae in the Fynbos Blome Institute of African Ornithology, University of the Western Cape. Photo: Anthony Mills. of Cape Town Mainland floras, such as the ancient Metrosideros (Myrtaceae family) is a occurs along the streams of the south­ and stable continent of Africa, combine classic example of an island genus, western Cape, with an outlying popula­ many lineages of plants in a plethora of having radiated widely in the Pacific. tion on the Gariep River. We have no orders, families and genera. Hence we Yet Metrosideros angustijolia pops up idea how Metrosideros reached Africa, have the floristic richness of the south­ in what seems to be the most unlikely or why it succeeded among the hun­ western Cape, where not only are fYnbos of places. It is an integral part of the dreds of shrub genera already crowding and succ~lent Karoo extremely diverse Fynbos Biome - as far as possible from the Western Cape. within themselves, but several distinct the Pacific, and where every niche of Apart from our species, all of the fifty­ floras (fYnbos, Karoo, forest, thicket, shrubs seems already to be filled by odd species of Metrosideros originate and even savanna) can share a single diverse orders, families and genera. from New Zealand, New Caledonia, New mountain range. Oceanic islands, by Metrosideros angustijolia, restricted Guinea and the Philippines in the west contrast, have relatively few lineages. entirely to the western part of South to the Marquesas and Hawaii in the This is because only a few lucky plants Africa, is a nondescript shrub. Although east. Even Australia lacks any native manage to cross the vast barriers of the called 'lance-leaf myrtle,' it remains member of this oceanic genus, although sea, drawing on their genetic plastic­ anonymous among the many narrow­ this island continent borders the Pacific ity to fill the vacant niches offered by leafed, sclerophyllous evergreens of the and is dominated by various Myrtaceae. isolated mountains erupted from the Fynbos Biome. The distribution of this Most species of Metrosideros are at ocean floor. Or, at least, so we learn species is unaccountable for a genus home on volcanic soils. By contrast, from textbooks... otherwise restricted to Pacific islands: it M. angustijolia is unknown from the 100 June 2006 Veld&Flora volcanic parts of South Africa, prefer­ ing gardens' are typical of New Zealand, the showy, bottlebrush-like blooms typ­ ring wet, acidic soils in the form of the which had few arboreal herbivores ical of Metrosideros and many other sandstone stream gravel of the Western before the introduction of the Australian members of the Myrtaceae family have Cape. brush-tailed possum (Trichosurus vul­ been lost, which is surprising in a land Gardeners in South Africa know pecula). Metrosideros has not penetrat­ of proteas and sugarbirds. Instead, M. Metrosideros not as our indigenous ed the most similar habitat in Africa: angustifolia has dull flowers pollinated shrub, but as an eye-catching tree, the island-like patches of yellowwood by insects. Conforming to the unre­ M. excelsa (pohutukawa). The red bot­ forest found from Knysna northwards markable shrubs such as Myrica (now tlebrushes attract sunbirds in South to Ethiopia. I can only speculate that Morella), Brabejum, Brachylaena, Rhus African gardens. But how many readers this exclusion has been owing to the and Freylinia sharing its streamside appreciate that it is not only birds, but presence of baboon, tree hyrax and scrub among the Cape mountains, the also geckoes (Hoplodactylus) that pol­ elephant. genus has used its remarkable genetic linate M. excelsa on its islands of origin Stranglers are not parasitic in the plasticity to abandon weird growths and in New Zealand? There, it can grow sense of mistletoes. They grow from the pretend to extreme ordinariness. so close to the shore that its roots are canopy down, not from the ground up, Many plant species introduced by bathed in seawater. and initially absorb nutrients from dust humans from other lands are now The species most famous among bota­ by means of aerial roots. They produce invading South Africa as if they belong nists is Metrosideros polymorpha, which wood as these roots grow down the here. Botanists see these as triffids, and dominates the natural forests of some host's bole, consolidating and merging respond with the chainsaw. However, of the most remote of islands. This as the plant finally finds a rooting me­ what if such colonizations have always Hawaiian species shows the remarkable dium in the ground. It may be unre­ been business-as-usual in the full­ plasticity of form in Metrosideros, shape markable that figs fashion a bole of their ness of ecological time? Although shifting to fill otherwise empty niches. own in this way, because their wood is Metrosideros is capable of being a tall Metrosideros polymorpha is one of the so soft that the distinction between root tree, it has descended to the com­ most variable species of plant on Earth. and stem is academic. However, nobody mon denominator of the tynbos shrub. It can be a stunted shrub colonizing understands how Metrosideros manages Accepted as not only indigenous but fresh lava-flows, a rounded cushion to form hard, dense heartwood within actually endemic, it is taken for granted only 15 cm high in montane bogs, an the initially cylindrical bole formed by by the Working for Water project as part epiphyte or the dominant tree (up to roots encompassing the host tree. After of the solution, not part of the problem. 25 m high) in tall forests - with accord­ all, the name is derived from the Greek Am I being over-optimistic by choosing ingly variable leaves over the full range metra (heartwood) and sideron (iron). to see, in M. angustifolia, the pacific of altitudes on Hawaii and its asso­ Metrosideros excelsa is not an epi­ face of problem plants? These seem ciated volcanic islands. Metrosideros phyte or a strangler but, for unknown threateningly alien at first, but are per­ polymorpha can survive being buried reasons, produces aerial roots when it haps destined to assimilate as welcome in lava, regenerating its roots once the becomes a mature tree. This and other variegations in the olive-green tapestry volcanic ash has cooled. species of Metrosideros often sport the of the future South Africa. fJ Other species of Metrosideros are genetic mutations of variegated leaves. creepers. M. perforata clings tightly to Further evidence of genetic plasticity is bark by means of sucker-roots as it that variegated trees in gardens often climbs trees in the form of a delicate revert to the normal green colour on ivy. Then the same species lets it all individual branches - as if in control of hang down when mature, as an unre­ the mutation. cognisably different woody liane of thick Metrosideros umbellata (southern 'monkey ropes.' rata), although rarely a strangler, is Metrosideros robusta (northern rata) also weird. Near Auckland, forests of of New Zealand is a strangler, an island this species present a 'chaotic spectacle re-invention of the strangler figs (Ficus) of gnarled, leaning trunks... Massive of tropical mainlands. It germinates as branches twist, dip and wind for metres. an epiphyte in the canopies of trees Trunks may rise a short distance from such as Podocarpus, the Pacific rela­ the surface, bend at a right angle to tives of African yellowwoods. It then extend parallel to the ground for 5-10 m sends down aerial roots that eventually and then grow vertically to reach the reach the ground, coalescing on the canopy. Serpentine trunks loop along way to form a hollow bole that gradually the ground' - in the words of scientists extirpates and replaces the host tree. Matt McGlone and John Hunt. John Dawson and Rob Lucas illustrate The only odd aspect of the South the reptilian demeanour of this growth African species is that it has reverted on page 49 of their new book The to normality. Metrosideros angustifolia nature of plants: habitats, challenges gives no hint of its genetic legacy as a ABOVE: A Pacific interloper, masquerading as an indigenous shrUb? Few botanists give a second and adaptations (CSIRO Publishing, creeper, epiphyte, strangler or bearer of thought to Metrosideros angustifolia as a native Melbourne, 2005). Once it becomes a aerial roots. Not in evidence is the dwarf­ of South Africa, but the other 50-odd species freestanding tree, Metrosideros robusta ism seen in the bonsai-like shrubs, or occur in the Pacific, and this genus is absent from itself becomes festooned with various the gigantism seen in the tall or stout islands in the Indian or Atlantic Oceans as well as all other continents. Photo: Anthony Mills. non-strangling epiphytes. Such 'hang- trees of Hawaii and New Zealand. Even June 2006 Veld&Flora 101.